This paper describes an experiment for assessing the discomfort glare caused by light emitting diodes (LEDs) having different colours. The results showed that coloured LEDs induce more discomfort glare than a white LED. On comparing different coloured LEDs, blue ones gave the highest glare perception, especially for those having shorter peak wavelengths. Different earlier proposed luminous efficiency functions for discomfort glare were applied to re-define luminance. This led to modified unified glare ratings, which achieved very accurate predictions of the visual results. A modified brightness based on a colour appearance model for unrelated lights was used to predict glare and also performed very well.
Consideration is being given to the adoption of a new metric characterizing light as it affects the human circadian system. Much has been learned over the past couple of decades about light as a stimulus for circadian system regulation, so it is appropriate that these discussions take place. The present paper develops an argument for adopting circadian stimulus as a metric for quantifying light in architectural spaces. The circadian stimulus metric (a) was developed from several lines of biophysical research, including those from basic retinal neurophysiology; (b) has been validated in several controlled experiments; and (c) has been used successfully in a number of real-world applications. Any discussions of new metrics should take each of these foundational points into consideration.
Although visual display terminals have been used in office work for many years, research on the effect of long time work using them is still insufficient. Also, the impact of a LED light source for all day work is not clear. In this paper, the visual fatigue caused by long-term VDT work under fluorescent and LED luminaires was investigated though subjective reports of symptoms, ophthalmological parameters and physiological signals. The results show that visual fatigue becomes more serious with increasing time spent at VDT work. Compared to fluorescent luminaires, the LED luminaires produced significantly greater near point accommodation, blink amplitude and oxygen saturation but less dry eye symptoms, less best corrected distance visual acuity and less high-frequency electrocardiogram power as time passed, although all were of small effect size. Although the participants carried out eight hours of VDT work under the two light sources, at the end the symptom ‘tired eyes’ was rated as moderate while all the other reported symptoms were rated as slight.
This paper deals with the modelling of the mesopic detection sensitivity data described in Part 1. The modelling is based on a linear combination of the spectral sensitivity templates of four retinal mechanisms (long + medium wavelength sensitive cones, rods, short wavelength sensitive cones and long - medium wavelength sensitive cones opponency) to describe the experimental data on mesopic detection sensitivity and to provide a practically usable model. Model parameters representing the weighting of these mechanisms are analysed as a function of target eccentricity and background luminance.
Various emerging technologies encourage the embedding of intelligent and climate responsive behaviour into architectural elements. Light-shelves have been used for decades to enhance natural light in spaces, however, their static nature is limiting their overall performance potential. This paper explores the convergence of rapid prototyping, parametric design and environmental modelling software to create a dynamic and direct-reflection daylight redirection system that significantly enhances daylight availability. A Radiance-based simulation workflow to optimise and study the system is used and a 1:1 mock-up is developed. The mock-up is based on a horizontal-light shelf with an array of mirror tiles that can tilt in two axes based on sun position. The potential impact of such a system is then evaluated for a side lit office space in multiple climates in the northern hemisphere. Results show that daylight can be redirected deep into the building more effectively and therefore improve daylight availability for otherwise underlit floor plan regions. Projected savings for electric lighting range from 17% to 35% compared with a static redirection system.
Indoor lighting is facing a massive retrofit to LED lighting. Research is needed to assess whether LED-based lighting can promote energy efficiency, boost visual comfort and support biological functions. This field study considered the lighting of four identical classrooms in an upper secondary school in Helsingborg, Sweden. Two classrooms were fitted with state-of-the-art ceiling pendants containing T5 fluorescent tubes and that had a direct/indirect light distribution (the control rooms). The other two classrooms were fitted with an experimental LED indirect lighting system (the experimental rooms). In the classrooms, 72 students aged 17–18 years performed their usual educational activities over a whole academic year. The light environment, electricity consumption, and students’ mood, light perception and saliva cortisol concentration were monitored. The two lighting systems produced only marginal differences. Overall, the experimental rooms were slightly preferred but achieved only small energy savings due to high parasitic losses.
It is well known that one of the problems of the current method for discomfort glare evaluation, called the unified glare rating, is the non-uniform luminance of the glare source. This paper addresses this issue by considering the spatial contrast of luminance as a measure of non-uniformity. An image-based metric is proposed to evaluate discomfort glare by modeling the neural response of human vision. The model takes an absolute luminance image as input and predicts visual discomfort based on the spatial distribution of the luminance of the stimulus and the background. The developed model was tested to predict subjective glare ratings based on an experiment conducted using non-uniform LED sources with symmetric and asymmetric patterns of LEDs, and its performance was compared with the unified glare rating. As expected, the unified glare rating predictions correlated well with the subjective glare evaluations of luminaires with symmetric patterns of LEDs (as they appear less non-uniform) but not for those with asymmetric patterns. Results showed that the developed model, named the Neural Response-based Glare Model, gave similar performance to unified glare rating for symmetric patterns but outperformed UGR for asymmetric patterns of LEDs.
An experiment was carried out to investigate how contrast threshold for target detection is affected by the presence of glare and by extraneous light sources using the method of ascending limits. The target was located at either a foveal or a peripheral (10° right) location, glare was adjacent to the foveal location, simulating the headlamps of an oncoming vehicle, and extraneous light sources were at either foveal or peripheral (10° right or left) locations. Contrast threshold for a foveal target without glare was affected mainly by the surrounding local luminance distribution. However, in the presence of glare and also for the peripheral target (both with and without glare) the global luminance distribution matters. Glare increased the contrast needed for detection of the foveal target, but this effect was reduced by the presence of extraneous light sources that were peripheral to the target. For peripheral targets, contrast threshold was also reduced by the presence of extraneous light at a non-target location and this effect was increased in the presence of glare. Glare equations tend to be based on tests using uniform, homogenous fields: these data indicate that, in the presence of extraneous light sources, the influence of glare is overestimated.
Due to different visual tasks and gaze patterns, the discomfort glare experienced by pedestrians may differ from that experienced by drivers. This paper investigates the discomfort glare experienced by pedestrians under various urban LED luminaires through psychovisual experiments conducted on a test track. The ability of state-of-the-art models to predict the level of discomfort glare, measured on the de Boer rating scale, for this application is also investigated. With one exception, the models all overestimate the mean subjective discomfort glare compared to the experimental data. Models proposed by Lin et al. (2015) and Bullough et al. (2008, 2011) perform well. However, the implementation of these models is not straightforward because choices are needed to estimate some of the variables such as the background luminance and the glare source area.
This paper introduces a software toolbox designed for the optimisation of white light generation using multiple light-emitting diode (LED) channels. The toolbox solves two separate types of multi-colour optimisation problems. These are the multi-channel mixing and the channel choice problems. In the multi-channel mixing problem, it is assumed that the available LEDs are pre-determined and fixed. The toolbox obtains the individual channel intensities that solve a constrained optimisation problem based on the mixed output light. It provides the user with the flexibility to choose an arbitrary formulation for the optimisation problem as well as various mathematical metrics to represent the different properties of the output light including colour rendering, power efficiency and colour accuracy. For the channel choice problem, the toolbox solves for the number and type of used LED channels as well as the intensity of individual channels to assist in optimal choice of deployed channels for luminaire manufacturing applications. This paper describes the graphical user interface and the back-end formulation of the optimisation problem and presents experimental results obtained by utilising the toolbox in a full-size conference room with 5-channel LED luminaires.
The photopic luminous efficiency function (V()) is used internationally for the definition of light output from electric light sources (lumens) and thereby for regulating minimum luminous efficacy requirements (lumens per watt) for the manufacture and sale of light sources. V() has, however, a long-wavelength spectral bias with respect to the overall spectral sensitivity of the human retina. When used in luminous efficacy regulations, the long-wavelength spectral bias of V() effectively penalizes many of the benefits expected from lighting that can be provided by short-wavelength light (e.g. scene brightness, colour rendering, circadian regulation and off-axis detection). Regulators must use ad hoc reductions to luminous efficacy requirements for ‘cool’ light sources to ensure that lighting benefits can be provided to society. These reductions would be unnecessary if a luminous efficiency function representing the overall spectral sensitivity of the human retina were used instead of V() in luminous efficacy regulations. The universal luminous efficiency function (U()) is proposed as a replacement. Utilization of U() would obviate ad hoc adjustments to regulations for ‘cool’ light sources, minimize wasted electric power imposed by regulations based upon V(), and perhaps most importantly, encourage manufacturers to produce light sources that efficiently provide multiple benefits to users.
Flashing yellow warning lights are important for worker and driver safety in work zones. Current standards for these lights do not address whether and how they should be coordinated to provide directional information to drivers navigating through work zones. A field study was conducted to assess driver responses to warning lights. The luminous intensities and flash patterns of warning lights along a simulated work zone were varied during daytime and nighttime. During the daytime, driver responses were relatively insensitive to warning light characteristics, although drivers preferred sequential and synchronised flash patterns over random, uncoordinated flashing. At nighttime, the combination of a temporal peak luminous intensity of 25 cd and a sequential flash pattern was optimal for providing directional information. A single initial warning light having a higher luminous intensity may help drivers detect the work zone without creating unacceptable visual discomfort.
Innovative daylighting systems (IDS) are used to deliver daylight into windowless spaces and building cores. Cleaning the exposed surfaces is essential for maintaining their efficiency because the accumulation of dirt inhibits their effectiveness. However, a review of the literature has indicated that this issue has not received the attention it deserves. This study reviews the cleaning methods currently used for solar devices and conventional daylighting systems. It also presents the technologies that can currently be employed to produce an IDS cleaning system, and suggests six cleaning mechanisms and 12 cleaning systems that suit different types of IDS in various operating circumstances. These include air-blowing, water-jetting, dragging-contact, rotary-contact and certain aid treatments. Air-cleaning and washing with water can both be used to restore functionality. Wiping and scrubbing are effective for increasing efficiency. Further productivity can be obtained by drying solar collectors after they have been washed. The systems suggested herein can be developed using already available technologies in order to achieve the ultimate in IDS efficiency restoration. However, before this can be done, the economic, environmental and operational aspects, in addition to potential levels of efficacy and applicability, must be assessed.
The relationships between environmental features and older people's ability to safely move around a complex pedestrian environment are, as yet, poorly understood. Specifically, the impact of light levels on trip hazard detection during walking has received relatively little attention. This study investigates the effect of illuminance on people's ability to detect steps of different heights in a laboratory-based controlled environment. Sixteen young and 15 older participants walked along a 13.2 m walkway towards an either ascending or descending step at 200 lux or 4 lux light levels. Trial time, gaze behaviour and distance at which the step was first visually fixated (detection distance) were measured using an eye-tracker. It was found that both the trial time and detection distance of older participants were affected by light level whereas the fixation number and fixation duration of young participants were affected by step-height. Shorter detection distance, greater number of fixations and longer fixation duration were found among older participants as opposed to young participants. The results suggest that the processing efficiency for visual information on an upcoming step is slower among older people than among young people. This implies that the vulnerability of older pedestrians maybe be reduced if better lighting or a simplified visual environment is provided.
Light source colour quality is a complex phenomenon with several visual and cognitive components. Subjective colour preference, naturalness and vividness assessments of reddish cosmetic products in a viewing booth lit by light sources with a correlated colour temperature of 3200 K and to 550 lx were analysed and modelled by a new combined colour quality formula – a linear combination of a colour fidelity index and a measure of chroma change. Results of the warm white light sources described in all three parts of this work were merged. They were modelled by optimising the parameters of the same formula. The formula supports multi-LED light sources with moderately accentuated local spectral maxima to enhance object chroma over a moderate range.
Mesopic threshold detection sensitivity was investigated by projecting quasi-monochromatic incremental targets with 22 centroid wavelengths between 422 nm and 652 nm onto different backgrounds. Every detection target was observed by at least nine subjects under eight different viewing conditions: two mesopic luminance levels (0.1 cd/m2; 1 cd/m2) and four eccentricities of target appearance off the visual axis (0°, 2.65°, 10° and 20°). Results were expressed in terms of absolute detection sensitivity values, i.e. inverse increment radiance values for each target at the detection threshold in sr·m2·W–1 units. In this part, the experimental method is described, and the dataset is analysed in terms of retinal mechanisms.
Whiteness is an important characteristic for surface colour, which is affected by the spectral power distribution of the illumination due to the fluorescent whitening agents contained in many white objects. The CIE whiteness metric has been widely used but is known to have limitations. For example, the boundary noted by the metric is not considered large enough, because, in many cases, a surface whose chromaticity lies outside the boundary can still be perceived as white. Further, the metric is only defined to characterize the whiteness of a surface under CIE Illuminant D65, and thus it should not be applied in other lighting conditions or to other light sources. This paper describes a psychophysical study, investigating the whiteness of 50 samples (12 paper and 38 textile samples) under 12 lighting conditions with different levels of correlated colour temperature and ultraviolet radiation. An optimized whiteness metric and a boundary of the white region based on the CIE whiteness metric were derived from the results, which can be used to precisely measure the whiteness of a surface under any lighting condition and to guide spectral engineering for LED sources.
The spectral composition of the light that reaches any indoor work plane depends on the characteristics of the light sources and the spectral reflectances of the surrounding surfaces due to the multiple reflections experienced by the light rays along their paths from the source to the observation point. We show that in indoor spaces, the source and surface radiances must obey a definite self-consistent relationship derived from the fact that each illuminated surface point acts as a secondary source of light. It is then established that the spectral irradiance on any plane is linearly dependent on the spectral radiance of the light source. The explicit integral form of this relationship provides a theoretical framework for a quantitative description of the surface effects. Additionally, under very general assumptions, we show that the spectral irradiance can be computed from the spectral flux of the source through a simple multiplication by a wavelength-dependent function. This function, with units of inverse surface (1/m2), provides a convenient way for evaluating the effects that arbitrary changes in the source spectrum will produce on the spectral irradiance at the indoor point under study.
This paper illustrates the results of daylight glare simulations of a simple office carried out using five different five weather data files (Chinese typical year weather, CSWD(C), CSWD(A), international weather for energy calculations and Meteonorm), for three Chinese locations (Beijing, Shanghai and Guangzhou). The aim is to analyse the impact of choosing one weather file or the other on the prediction of daylight glare in the interior environment. The results show that using the Chinese typical year weather and CSWD(C) files can make a better prediction of the time distribution of daylight glare than the others. Analysis of the total amount of daylight glare leads to the conclusion that the Chinese typical year weather file should be recommended when considering extreme weather conditions and the CSWD(C) or Meteonorm files should be recommended in normal weather conditions.
How we look at other people may affect conclusions drawn about the effect of changes in lighting when this task needs to be done after dark. This paper reports further analysis of the distance and duration of fixation on other pedestrians, updating a previous review by considering a greater number of fixations and by examining the influence on these of other characteristics such as the relative direction of travel. This analysis provides further support for a tendency to fixate others at a distance of 15 m and for a duration of 500 ms.
Architectural lighting design is generally believed to have visual and psychological consequences on humans, and has been investigated either as an artistic or a scientific endeavour. This paper explores the possibility that these two viewpoints are not mutually exclusive with a poetic approach. It builds upon two arguments: the first is that poetry, being an inherently compositional system like language, impacts the perceived meaning of lit environments; the second is that humans seek qualities with experiential richness when interacting with lit environments, which is very much aligned with poetry. This reasoning is supplemented by reflections on the poetic possibilities within realised projects used as simple artistic and scientific case studies to demonstrate this complex visual and psychological interplay. Opinions from academics and professionals from the field of architectural lighting design are sought on these poetic possibilities, the appropriateness of these realised projects in expressing their respective qualities, and on the role of poetics in architectural lighting design in general.
Two psychophysical experiments were conducted to investigate the effect of colour gamut size and shape on colour preference. In the first, two side-by-side booths were designed to resemble a retail setting with clothing; in the second, a single booth was designed to resemble a restaurant setting, but also included a mirror to permit the observer's evaluation of skin tone. These settings were illuminated with two sets of sources, where, compared to a fixed reference, one set created modest chroma enhancement and the other set created greater increases in object chroma. Within each set, gamut shape varied, meaning different hues were saturated, even though, on average, the spectra created the same average increase in chroma. When objects were unfamiliar, as with the fabrics, all chroma-enhancing spectra were preferred to the fixed reference regardless of the gamut shapes. When familiar objects were present, such as food, observers were more discerning about changes in chroma and hue. We conclude that a graphic of gamut shape is an important adjunct to average measures of colour fidelity and gamut.
For wayfinding signage it is essential that the sign is conspicuous and that the messages it contains are legible. This study investigated the optimal luminance for internally lit wayfinding signs in Swiss railway stations. The results demonstrated first, that increasing the light output of the LEDs inside the sign improved conspicuousness of the signage against its surroundings, and second, that considerable improvement of the signage’s legibility could only be observed until its white text reached a luminance of 100 cd/m2. Hence, for internally illuminated signage in general indoor situations, a luminance of 100 cd/m2 is recommended. Very high luminances should be avoided because even if conspicuity is improved, legibility might worsen.
An experiment was conducted to evaluate how subjective impressions of a light source’s colour quality depend upon the details of the shifts it causes in the colour appearance of illuminated objects. Twenty-eight participants each evaluated 26 lighting conditions in a 3.1 m by 3.7 m room filled with objects selected to cover a range of hue, saturation, and lightness. IES TM-30-15 Fidelity Index (Rf) values ranged from 64 to 93, IES TM-30 Gamut Index (Rg) values ranging from 79 to 117, and IES TM-30 red chroma shift (Rcs,h1) values ranging from –19% to 26%. All lighting conditions had the same nominal illuminance and chromaticity. Participants were asked to rate each condition on eight point scales for saturated–dull, normal–shifted, and like–dislike, as well as classifying the condition as one of saturated, dull, normal, or shifted. The findings suggest that gamut shape is more important than average gamut area for modeling human preference, with red playing a more important role than other hues. Average fidelity alone is a weak predictor of human perception, especially CIE Ra. Nine of the top 12 rated products had a CIE Ra value of 73 or less, which indicates that the criteria of CIE Ra ≥ 80 may be excluding many preferred light sources.
Road delineation treatments enhance the ability of drivers to control their vehicle safely on winding roads. A simulator experiment compared night-time driving on a country road under three conditions: on an unlit road, on a road illuminated on curves by typical road luminaires, and on a road with an active lane delineation application, where self-luminous road studs are turned on to outline the lane and road edges as the driver approaches and passes the curves. The unlit condition induces greater lateral position variability and longer crossovers relative to the studs condition, demonstrating better lateral vehicle control in the latter. The luminaires condition induce greater lateral position variability in left curves, and longer crossovers in right curves, relative to the studs condition, which also demonstrates a better lateral vehicle control in the studs condition. At a subjective level, the participants perceived both the studs condition and the luminaires condition as safer, more comfortable and allowing better control than the unlit road. It was concluded that the tested application enhanced the ability of drivers to control the virtual car, as compared to an unlit road or road lighting.
Visual discomfort is predicted from a luminance map with a model based on the receptive field mechanism in the human eye. A centre-surround receptive field is described by a Difference of Gaussians. Eight commercially available office luminaires are assessed for visual discomfort in a paired comparison experiment. The correlation between the subjective data and the receptive field model is optimized for three factors: the centre Gaussian width, the surround Gaussian width and the centre-to-surround weighing factor (WF). A centre and surround visual angle of 0.53 and 2.19 min arc, respectively, and a WF of 0.87 result in a coefficient of determination of 0.77. The model is validated independently with magnitude estimation data obtaining a coefficient of determination of 0.82. Where the standard unified glare rating method fails (coefficient of determination of 0.45), the receptive field model ameliorates predictability for visual discomfort. The model based on receptive fields is promising to replace current standard glare metrics, specifically when non-uniform luminaires are to be evaluated.
As lighting researchers we can learn from our colleagues in the humanities who have progressed qualitative research methods to a high level of rigour. We should consider using qualitative research methods more. Such methods allow exploration of complex issues involving human views and behaviour, and help researchers address difficult to answer questions that otherwise go unanswered. Good quality qualitative research can provide rich explanations of what went on in a given situation. Validity and reliability are considered differently with this type of research methodology. This paper attempts to identify when qualitative research is appropriate, what questions it can answer in lighting research, how it is done, list the features and provide a simple brief example of a post occupancy evaluation case study. It is argued that qualitative research can be used with quantitative research; before quantitative research to inform it or afterwards to explain it; but it can also be extremely informative in itself and act as a catalyst for change to readers who can see the outcomes in a context that applies to them.
This paper investigates the illuminance needed to detect trip hazards for pedestrians walking after dark. In previous work, it was assumed that the critical obstacle height is 25 mm: further review of accident data and foot clearance data suggests instead that 10 mm is the critical height. Eye tracking records suggest a tendency for obstacles to be detected approximately 3.4 m ahead. Interpretation of obstacle detection data suggests horizontal photopic illuminances of up to 0.9 lux are required for peripheral detection of a 10 mm obstacle 3.4 m ahead, according to the scotopic/photopic ratio of the lighting and the age of the observer.
Two formulae currently exist for calculating mean room surface exitance. This research note explains and demonstrates that one of these formulae is erroneous under certain conditions and stresses that the alternative expression should generally be used for computing mean room surface exitance.
We present a novel freeform lens design method for application to light-emitting diode collimating illumination. The lens is designed with a point-source assumption to form compact collimators. The method is derived from a basic geometric-optics analysis and the associated construction approach. By using this method, a compact collimating lenses with an aspect ratio = 0.181 is developed. With optimization of initial parameters, a highly collimating lens for a Cree XP-E LED (chip size: 1.2 mm x 1.2 mm) with an optical efficiency of 88.5% under a beam angle of ± 1.9° is constructed by simulation. To verify the practical performance of the lens, a prototype of the collimator lens is also made. This has light distribution compatible with the simulation results.
Discomfort glare is a major challenge for the design of workplaces. The existing metrics for discomfort glare prediction share the limitation that they do not take gaze direction into account. To overcome this limitation, we developed a ‘gaze-driven’ method for discomfort glare assessment. We conducted a series of experiments under simulated office conditions and recorded the participants’ gaze using mobile eye tracking and the luminance distributions using high dynamic range imaging methods. The two methods were then integrated to derive ‘gaze-centred’ luminance measurements in the field of view. The existing ‘fixed-gaze’ and the newly developed ‘gaze-driven’ measurement methods are compared. Our results show that there is a significant difference between the two methods. In this paper, the procedure for integrating the recorded luminance images with the recorded gaze dynamics for obtaining gaze-centred luminance data is described. This gaze-centred luminance data will be compared to the subjective assessment of glare in Part 2 of this study.
Neonatal intensive care units are a special lighting design challenge. Although natural light is highly desirable, it should be carefully planned to maximise benefits and minimise the problems associated with uncontrolled sunlight. This paper discusses the performance of different passive sunlight control strategies in a neonatal intensive care unit at the Dr. Humberto Notti Children's Hospital in Mendoza, Argentina, analysing their annual daylight behaviour through dynamic daylight simulations. The aim of this work is to optimise the use of daylight in neonatal intensive care units, considering the special lighting conditions required. Results show that, in this case study, the adequate implementation of solar control systems and the appropriate layout of the space for different uses according to surrounding building design and the characteristics of the local luminous climate can increase the useful daylight illuminance by up to 13%, while avoiding the incidence of direct sunlight at all times.
An experiment was conducted to evaluate intellectual productivity in three lighting conditions: (a) conventional ambient lighting, (b) task ambient lighting with normal colour temperature (5000 K) and (c) task ambient lighting with high colour temperature (6200 K). In the experiment, cognitive tasks were given to 24 participants. The concentration time ratio, which is a quantitative and objective evaluation index of the degree of concentration, was measured. The results showed that the average concentration time ratio under the task ambient lighting with high colour temperature was 72.5%, which was 5.0% points higher than that under the conventional ambient lighting. It is believed that intellectual work can be performed better when the concentration time ratio is high.
The discovery of a novel non-rod, non-cone photoreceptor in the mammalian eye that mediates a range of ‘non-visual’ responses to light has required reexamination of how lighting needs for human health are characterised and evaluated. Existing literature provides useful information about how to quantify non-visual spectral sensitivities to light but the optimal approach is far from decided. As more is learned about the underlying biology, new approaches will continue to be published. What is currently lacking is a flexible framework to describe the non-visual spectral effectiveness of light using a common language. Without a unified description of quantities and units, much of the value of scientific publications can be lost. In this paper, we review the existing approaches by categorising the proposed quantities depending on their application. Based on this review, a unified framework is provided for use in evaluating and reporting the spectral effectiveness of light for human health. The unified framework will provide greater flexibility to model the non-visual responses to light and is adaptable to a wide range of lighting solutions of interest to researchers, designers and developers. A new visualisation tool, the SpeKtro dashboard, is available to explore the unified framework online at spektro.epfl.ch.
In this paper, a gesture-based control system for smart lighting management is introduced. The system consists of multiple depth camera sensors that track the users’ positions, movements and gestures in real-time and forward the data to the main computer where the lighting control commands are generated. The implementation was built into the ‘ResponseRoom’ R&D environment, where two different lighting controls in a real-time installation were validated with the ability to dim and control colour by hand gestures. In order to study end user preference and to discover needs and guidelines for future development of the system, a user survey on gesture-based lighting control in a meeting room application was carried out. In the survey, no predetermined gesture vocabulary or real lighting control implementation were used. Instead, the respondents could freely develop their own gesture commands. Altogether 197 gained responses are analysed. The results reveal that generally intuitive control gestures are difficult to generate as there is a rather strong variability in personal preferences. The most popular gestures in the user survey were used by 25–30% of the respondents, 19% of all user responses in the test were multimodal combinations of different gestures, verbal expressions and sounds.
There is uncertainty in every daylighting calculation, an inherent and unavoidable imprecision which exists in addition to any error due to inaccuracy in a numerical model. It occurs because neither the future state of a building nor the future luminance pattern of the sky can be predicted with certainty. This paper examines the propagation of error in a daylight coefficient calculation and concludes that the overall effect of uncertainty in the various parameters is significant and must be taken into account in practice.
The theory of daylight coefficients is extended. The daylight factor under a uniform sky is shown to be equal to twice the mean of the daylight coefficients, making it possible to compare criteria used in climate-based simulation with older daylighting standards. Simple examples are used as illustrations, with theoretical working and numerical experimentation. Guidelines are given for good practice.
This paper describes a psychophysical experiment conducted to investigate the perceived colour rendering properties of LED light sources as regards colour fidelity. The grey scale method was applied to assess the colour differences of identical samples placed in two side-by-side cabinets. Ten observers participated to evaluate 30 samples under nine pairs of light sources at three correlated colour temperatures. It was found that CAM02-UCS colour space correlated with perceived colour differences best among all those tested. Furthermore, the results showed that all the colour fidelity metrics gave similar good performance, including the CIE general colour rendering index, and markedly outperformed the metrics based on colour gamut.
An optimized model is established to improve the accuracy and efficiency of lifetime estimation for LED-based light bars. A Weibull function is used to fit test data of remaining luminance under two groups of accelerated stresses, and a method for determining the optimal test time is put forward. The results show that the optimized model for lifetime prediction best reflects the characteristic of luminance degradation. Furthermore, the error of the accelerated lifetime first decreases and then increases, finally decreasing again, which confirms that the method for determining the optimal test time is feasible given the level of accuracy required.
A psychophysical experiment was conducted to evaluate the performance of various colour spaces, colour difference formulae, colour matching functions and colour fidelity measures in predicting perceived colour differences. Ten observers evaluated the colour differences of 20 colour samples under 11 pairs of light sources. The results suggest that the colour differences calculated using the CIE 1964 colour matching functions in the CAM02-UCS colour space can predict the perceived colour differences. IES-Rf which used the 20 colour samples and the reference illuminants used in the experiment was highly correlated to the perceived colour difference. The importance of a uniform spectral sensitivity for colour fidelity measures is also identified.
Facial emotion recognition has been used as a representative pedestrian activity in studies examining the effect of changes in road lighting. Past studies have drawn conclusions using results averaged across performance with the six universally recognised expressions. This paper asks whether expression choice matters. A reanalysis of past data for each unique expression does not suggest a change in the conclusion that facial emotion recognition is not significantly affected by the spectral power distribution of the lighting.
The main advantages of high-frequency electronic ballasts for high-intensity discharge lamps are high luminous efficacy, small size, lightweight and longer lifetime. This is why high-intensity discharge lamps operating at high frequency are widely used. This paper proposes an approach for designing resonant circuit electronic ballasts controlled by frequency variation for high-intensity discharge lamps. The proposed technique including an AC/DC rectifier, a power factor correction circuit and a DC/AC half bridge inverter. These electronic ballasts offer a wide range of dimming controls and can avoid acoustic resonance. However, under dimming, the electric and photometric characteristics of the lamp change. In order to study these effects under the process of dimming, this work studies the lamp properties by varying both lamp power and operating frequency.
In this paper, the authors have calibrated a Raspberry Pi and Camera Module (RPiCM) for use as an absolute luminance sensor. The spectral response of the RPiCM chip as well as linear mapping to the standard CIE-XYZ colour space have been measured, calculated and presented. The luminance values are anchored to absolute luminance measurements. Further, by using high dynamic range imaging techniques making use of different shutter speeds in a sequence of images, the measurement of luminance values from approximately 10 to 50,000 cd/m2 is possible. Lens correction for vignetting is also addressed, while pixel point spreading is ignored. This measurement goes beyond a single point measurement, economically and accurately allowing each of the arrays within the RPiCM chip to act as an individual luminance meter over the entire field of view of the camera system. Applications and limitations of the embedded camera system are discussed. An Energy Plus model is constructed as a motivational application of a simple one room, one window space and simulated for a year using weather files from around the world. These simulations highlight the need for spatial luminance-based sensing within the built environment to counteract the experience of discomfort glare by building occupants.
The dimmability of light-emitting diodes (LEDs) offers lighting designers great flexibility in illuminating an indoor environment. However, even for experienced lighting designers, it is not easy to achieve both comfort and energy efficiency using large-scale lighting systems. To improve this situation, in this paper we propose the use of a quantitative human perception model for an illuminance distribution in an indoor environment. Based on this model, we can optimise the dimming levels of the LED lighting system given the positions and preferences of users. Enhancing user satisfaction and reducing energy consumption are jointly taken into consideration.
The recent trend for large-scale replacement of luminaires using discharge light sources with LED luminaires without any significant adjustments to the electrical installation has generated controversy. This study examines the main electrical measures in a large outdoor lighting installation before and after the replacement of a large number of metal halide floodlights with LED luminaires. The electrical parameters of both technologies are discussed in detail and compared, with special attention given to the odd-numbered harmonics of voltage and current, the generated wave deformation, currents in the neutral conductor, the wattless reactive volt amps and the peak inrush currents. At cold start-up, the LED luminaires generate large power-on currents, much larger than those generated by the metal halide lamps, despite requiring 36% less real installed power. This is a basic problem to be solved when planning a public lighting renovation with LED luminaires as the rest of electrical parameters are reduced. To address this problem, it is proposed to energise the luminaires using magneto-thermal protection circuits with slow trip curves that will tolerate the large short-term inrush currents.
Major factors to be considered when designing lighting for paintings include colour discrimination, colour diversity, clarity and the balance of cool–warm (bluish-yellowish) lighting. This paper concerns the last factor and presents two radiometric and one colorimetric methods of predicting cool–warm balanced illuminants. For a high correlated colour temperature, the spectral power distributions of Planckian and daylight-simulating illuminants are high in short wavelengths and low in long wavelengths and, therefore, appear bluish. The reverse is true for low correlated colour temperature illuminants, which appear yellowish. The balanced spectral power distribution occurs at 5000 K. MacAdam’s complementary powers function is psychophysical and represents the power of wavelengths across the visible spectrum required to neutralize (convert to white) their complementaries. Again the balanced power occurs for illuminants of 5000 K. Hence, a correlated colour temperature in the 4500–5500 K range is recommended for cool–warm balanced illuminants. This recommendation is supported by results of four recent experimental studies.
Museum lighting must use a light source suitable for preserving the colours of the objects being lit. This paper examines how prolonged exposure to three light sources typically used in museums affect the chromaticity of five pigments commonly used in Chinese traditional heavy colour painting. The three light sources were tungsten halogen with an infrared filter, metal halide and an RYGB-type LED. The chromaticities of the pigments were measured at regular intervals over 1152 hours of exposure. These data were used to reveal the chromaticity shifts occurring and hence the relative effect of each typical light source. Of the three light sources measured, the RYGB-type LED had the least chromaticity shift, on average. These results provide a database for related research on Chinese traditional heavy colour painting illumination and provide a more general reference for the choice of light source in the design of museum lighting.
Daylit architecture is perceived as a dynamic luminous composition, yet most existing performance metrics were designed to evaluate natural illumination for its ability to adequately illuminate a two-dimensional task surface and avoid glare-based discomfort. It may be argued that task-driven approaches based on surface illumination and glare ignore the likelihood that contrast can provide positive impacts on our visual perception of space. Advances in these metrics to accommodate climate-based sky conditions and occupant behaviour have improved our ability to evaluate task illumination and glare, yet the same attention has not been paid to evaluating positive perceptual responses to daylight. Existing studies have attempted to link subjective ratings of composition to simple global contrast metrics without reaching consensus. More advanced metrics have been developed in computational graphics and vision fields but have not been applied to studies in qualitative lighting research. This paper introduces the results from an online experiment where subject ratings of daylight composition are compared to quantitative contrast measures across a series of renderings. This paper will identify which measures correlate to subjects’ ratings of visual interest and introduces a modified contrast algorithm, which can be used as a novel prediction model for visual interest in daylit renderings.
For implementation of the mesopic photometry system in CIE 191:2010 to outdoor lighting, two simplified methods to measure the mesopic luminance are proposed. One of the methods, named the Adaptation Spectral Power Distribution) method, assumes that the spectral power distributions (SPDs) of reflected light at test points on the road surface are the same as that of the adaptation field. Another method, named the Source SPD method, assumes that the reflected light SPDs are equal to the SPD of the light source. Error simulations with a real road surface spectral reflectance dataset show that the error distributes over an 8% range due to the variation of the road surface spectral reflectance in the worst case. Although the bias due to the road surface spectral reflectances causes a large error with the Source SPD method, a proposed correction can reduce the error sufficiently. Error simulations also show that the Source SPD method is not so sensitive for lighting scenes that include multiple light source types. It has been shown that the SPD methods can measure the mesopic quantities without scotopic/photopic luminance meters having both V() and V'() detectors when both the adaptation field and test points consist of road surfaces.
In Part I of this work, observers scaled colour preference, naturalness and vividness visually on interval scales (0–100) labelled by semantic categories (e.g. ‘moderate’, ‘good’ and ‘very good’) in the context of office lighting. Five customary light sources without object saturation effect illuminated a table with coloured objects in a real room. The observers’ assessments were predicted by recent colour quality indices and selected pairs of indices combined linearly. Criterion values of the indices for ‘good’ colour preference and vividness were determined to provide a usable acceptance limit for the spectral design and evaluation of light sources. To predict colour preference, correlated colour temperature turned out to be useful. In Part 2 of this work, another experiment with the same method but using multi-LED spectra with more object saturation will be analysed and the two datasets will be merged.
In Part 2 of this work, observers scaled colour preference, naturalness and vividness visually on interval scales (0–100) labelled by semantic categories (e.g. ‘moderate’, ‘good’ and ‘very good’) in the context of food lighting using the same questionnaire as in Part 1. Seven multi-LED light sources with more or less object saturation effect illuminated a viewing booth with coloured food objects. The two datasets (Part 1: room + Part 2: viewing booth) were merged and the observers’ assessments were predicted by recent colour quality indices and CIELAB chroma differences. Linear combinations of selected pairs or triads of descriptors were used to predict the merged dataset. Criterion values to achieve ‘good’ preference, naturalness and vividness level were determined.
This paper proposes a new glare model for assessing discomfort glare caused by LED luminaires having different luminance uniformities. It has been derived from the glare rating data for different groups of LED luminaires representing different degrees of luminance uniformity. In total, 5040 glare ratings were collected. Unified Glare Rating was tested using these data. It was found that Unified Glare Rating under-estimates the glare perception produced by non-uniform luminance glare sources. Furthermore, two modified Unified Glare Rating models proposed by Tashiro et al. and by the present authors were tested. They both performed well when predicting the results for LED luminaires having different luminance uniformities.
Along with the high energy-efficiency potential, light-emitting diode (LED) lighting provides the possibility for spectrum control. Our study presents the original data on the influence of LED light spectrum quality on the growth and macro- and micro-nutrient uptake of lettuce (Lactuca sativa L. cv. Frillice) plants cultivated in indoor conditions and without daylight. Four LED light spectral combinations were investigated using conventional high-pressure sodium (HPS) lighting as a control. In general, the LED light spectra were more favourable than the HPS light spectrum for promoting the growth and nutrient uptake of plants. In particular, the light spectrum provided by the combination of the far-red, deep-red and blue LEDs had the highest growth and nutrient uptake indices. This spectral combination particularly enhanced the uptake of potassium, calcium and magnesium in comparison to control plants grown under conventional HPS lamps. The uptake of iron and zinc were significantly influenced by the spectral changes of the red and blue light.
In CIE 191:2010, the Commission Internationale de l’Eclairage recommends a mesopic photometry system based on peripheral visual tasks. For implementation of the system, the visual adaptation field needs to be defined, taking into account the surrounding luminance effect on the state of adaptation. A series of vision experiments in the mesopic range has been conducted to measure the surrounding luminance effect with respect to the angle between a peripheral task point and a point source. The results show that the surrounding luminance effect at a peripheral task point decreases with increasing angle at a larger slope than existing models, such as the Stiles-Holladay equation, the Commission Internationale de l’Eclairage general disability glare formula and the Stiles–Crawford equation. A new model for the surrounding luminance effect is proposed.
In mesopic photometry, adaptation luminance is needed to derive the mesopic luminances for the measurement field. The average luminance of the visual adaptation field is considered as the adaptation luminance. The visual adaptation field has yet to be defined in terms of the size, shape, or location within the visual field. A study in three road lighting situations was conducted, in order to determine the feasibility of using the road surface as the adaptation field compared to circular or elliptical adaptation fields. Currently, the road surface is used as the measurement field for calculating road lighting. Using the road surface as the adaptation field resulted in 76–113%, higher average luminance than obtained using circular or elliptical adaptation fields when the road was bordered by a park. High-luminance sources outside of the visual adaptation field cause veiling luminance. Veiling luminance increases the adaptation state, but not the luminance within the measurement field. The bias veiling luminance can cause on mesopic luminance calculations was estimated to be less than 2%. The estimated bias can be considered trivial in practical road lighting measurements.
Although the development of high dynamic range images allowed broadening sky vault analysis for lighting research purposes, the sky classification is still performed using subjective methods. There is no established metric for comparison, only isolated approaches that do not address the characteristics of the images. This paper presents a proposed multidimensional method for analysing light from sky vault high dynamic range images. A Matlab routine was applied. It uses a classification system to check the relevance of each image attribute, choosing the most suitable sky model from the ISO 15469:2004 (CIE S 011/E:2003) standard. The results, that can be plotted or exported, indicate that the routine is able to choose the most relevant model for the photographed sky, thus allowing the creation of a sky classification database.
Light pollution is an environmental issue of rapidly increasing concern. Among the various types of light pollution, a major issue in residential areas is discomfort glare due to light trespass. Discomfort glare makes seeing and sleeping in a room difficult. Typical discomfort glare evaluation methods include the Daylight Glare Index and the Unified Glare Rating. However, no evaluation method exists for discomfort glare from artificial lighting entering through a window at night, i.e. light trespass. Therefore, this study investigated the existing methods for evaluating discomfort glare and subjective evaluation methods related to the characteristics of light trespass. We also examined the possible application of lighting simulation software programs for light trespass evaluation. We then performed a subjective evaluation of discomfort glare due to light trespass, compared the experimental values to our calculated values, and finally suggested a modified formula for evaluating light trespass.
CIE Joint Technical Committee JTC-1 has requested data regarding the size and shape of the distribution of drivers’ eye movement in order to characterize visual adaptation. This paper reports the eye movement of drivers along two routes in Berlin after dark, a main road and a residential street, captured using eye tracking. It was found that viewing behaviour differed between the two types of road. On the main road eye movement was clustered within a circle of approximately 10° diameter, centred at the horizon of the lane. On the residential street eye movement is clustered slightly (3.8°) towards the near side, eye movements were best captured with either an ellipse of approximate axes 10° vertical and 20° horizontal, centred on the lane ahead, or a 10° circle centred 3.8° towards the near side. These distributions reflect a driver’s tendency to look towards locations of anticipated hazards.
We introduce a way to simultaneously measure the light density, light vector and diffuseness of the light field using a cubic illumination meter based on the spherical harmonics representation of the light field. This approach was applied to six light probe images of natural scenes and four real scenes built in our laboratory, and the results were compared to those obtained using Cuttle’s method. We also demonstrated a way to simultaneously and intuitively visualise the global structure of the light distribution using light tubes and colour coding for the light density, light flow and diffuseness variations through the space. Together with Mury’s work, we have a complete way to describe, measure and visualise the local and global low-order properties of light distributions in three-dimensional spaces.
The purpose of this paper is to show a possible way to move forward to a usable method for lighting practitioners to characterise and optimise the colour quality of white light sources for general interior lighting. First, correlations between recent colour rendition (colour quality) metrics are analysed. Second, linear and quadratic combinations of the two recently published Illuminating Engineering Society of North America metrics (Rf and Rg) are suggested to approximate two selected visually relevant colour quality metrics, the Memory Colour Quality Index and the NIST Colour Quality Scale Qp index. Numeric values of the optimum coefficients of these (Rf, Rg) combinations are provided for a comprehensive set of 546 light source spectral power distributions in two correlated colour temperature groups, warm white and cool white. The performance of the different combinations used to describe the metrics ranged between poor and good.
The light density, direction and diffuseness are important indicators of the spatial and form-giving character of light. Mury presented a method to describe, measure and visualise the light field’s structure in terms of light density and direction variations in three-dimensional spaces. We extend this work with a theoretical and empirical review of four diffuseness metrics leading to a novel metric proposal DXia. In particular, the relationships between these diffuseness metrics were studied using a model named ‘probe in a sphere’. Diffuseness metric DXia re-frames the diffuseness metric of Cuttle in an integral description of the light field. It fulfils all diffuseness criteria and has the advantage that it can be used in a global, integrated description of the light flow and diffuseness throughout three-dimensional spaces.
This paper presents a detailed analysis of the capabilities of imaging luminance measuring devices for determining discomfort glare. Common opinions on light-emitting diode (LED)-based street lighting luminaires say these products cause high glare. This paper contains the results of calculations and thoughts on the potential measurement errors arising from the incompatibility of the measuring device parameters (number of pixels, sensor dimensions and focal length) to the resolution of the human eye. There are also some cases presented where this incompatibility is of the highest importance, i.e., for the luminance distribution measurements connected with identifying a discomfort glare problem caused, in particular, by multi-source LED luminaires.
We consider energy-efficient indoor lighting control for adapting to daylight and user presence changes. Light sensors located at ceiling luminaires and at workspace desks are used to provide illumination information feedback, along with user presence information from occupancy sensors at ceiling luminaires, to a lighting controller. The light sensors at the workspace transmit information at a lower update rate than the sensors at the ceiling. Using this sensing information, we propose a control method to adapt the dimming levels of the luminaires such that desired illumination levels are achieved at the workspace level. The performance of the proposed method is evaluated in an office lighting testbed.
The possibility of a spectrally tunable solar-like light source is drawing attention with the development of LEDs. We researched the market of high-power, monochromatic LEDs and established a database with 103 kinds of LED by a new model. We used the database to match the solar spectrum in the wavelength range 380–780 nm. The optimal combination maximising the fit to the solar spectral curve was obtained. The trade-off relationship between the selection of LEDs and the fit was investigated in detail. The results show that the optimal combination contains 34 types of LED with a maximum correlation index R2 of 88.67%. The value of R2 reduces to 85.06% when the number of LED types is reduced to 20, but the R2 value decreases sharply if the number of LED types is decreased to 16, with a R2 of 79.97%.
Compared to traditional street lighting technologies, light emitting diode (LED) luminaires have the potential advantages of increased energy efficiency, longer operating life and better light distribution. In this paper, we present a new high-quality LED road lighting luminaire. The luminaire shows high optical efficiency, high optical utilization factor and low glare, and illuminates the street with high uniformity. We verify its feasibility by Monte Carlo ray-tracing and test its real performance through a prototype model of the luminaire. The results show that it can achieve the expected performance.
Short-wavelength (<500 nm) output of light sources enhances scene brightness perception in the low-to-moderate photopic range. This appears to be partially explained by a contribution from short-wavelength cones. Recent evidence from experiments on humans suggests that intrinsically photosensitive retinal ganglion cells (ipRGCs) containing the photopigment melanopsin might also contribute to spectral sensitivity for scene brightness perception. An experiment was conducted to investigate this possibility at two different light levels, near 10 lx and near 100 lx. Subjects provided forced-choice brightness judgments and relative brightness magnitude judgments when comparing two different amber-coloured stimuli with similar chromaticities. A provisional brightness metric including an ipRGC contribution was able to predict the data with substantially smaller errors than a metric based on cone input only.
A two-degree bipartite field was used to investigate the influence of pulse width on human luminous perception. The frequency of the pulsed light was 100 Hz and the duty ratio was set to 1, 2, 5, 10, 20, 30, 50 and 70%. The results show that pulsed light has a brightness enhancement effect and that the enhancement effect changes when the wavelength and duty ratio are different. The maximum enhancement effect appears at 430 nm and the minimum at 460 nm. Then, a theoretical spectral luminous function for pulsed light as a function of wavelength and duty ratio was calculated using cone fundamentals. The newly established luminous function can be used to calculate the real brightness perceived by human eyes when people are exposed to a space illuminated by pulse-width modulation dimming lamps.
This paper investigates cyclists’ detection of an obstacle on the surface of the road ahead, observed in peripheral vision, and how this is affected by variations in light level from road and cycle lighting. The data analysed were the height at which a rising obstacle was detected, this simulating an approaching irregularity in the road surface. The results suggest that when cycling on a lit road, cycle lighting frequently offers no benefit for peripheral detection and may make it worse. It was demonstrated that position matters: At low illuminances, a hub-mounted lamp improved detection over a handlebar-mounted lamp. This benefit was sufficient to offset the reduction in detection found when decreasing road lighting from 2.0 lux to 0.2 lux.
The CIE Standard General Skies defines the luminance distribution of skies into 15 types, from overcast sky to clear sky. Finding the frequency distributions of such skies is not a simple task, for two reasons. The first is the need for accurate luminance measurements over a long period of time. Such data are not available in many regions around the world. The second is the difficulty in obtaining accurate readings for the zenith luminance in low latitude climates. This paper presents a method in which the horizontal sky illuminance can be used to classify sky type.
The CIE general colour rendering index (Ra) is still the only widely used and accepted colour fidelity index for characterising white light sources. However, user preference for light sources is not determined by fidelity alone but also by colour saturation. Here, we investigate the impact of fidelity and gamut area on the preference for white light sources in three application areas: fresh food, packaged food and skin tones. Thirty-four participants evaluated the attractiveness of object appearance for seven light sources with Ra values ranging between 70 and 100 and relative gamut area index (Ga) ranging between 90 and 120. Results show that object appearance was rated as more attractive for light sources with a larger colour gamut, which have Ra values of 80 and lower. In general, light sources with relatively high spectral power in the long wavelength range, enhancing red objects, received the highest preference. We conclude that, next to fidelity, colour saturation makes a significant contribution to the appreciation of a light source. We therefore propose using Ra in conjunction with Ga and a colour rendering graphic for providing a more detailed description of the colour quality of white LED light sources.
Three physiological factors (melatonin levels, tear mucus ferning quality and degree of asthenopia) were examined for their relationship to visual comfort. A lighting environment was created where the illuminance, illuminance uniformity and correlated colour temperature could be adjusted. A three-factor and three-level orthogonal experiment with 24 subjects was designed and carried out. The results indicated that the selected environmental factors had different impacts on the physiological factors. With the illuminance increasing, the melatonin level decreased significantly and the tear mucus ferning quality was improved. However, there is no general influence of illuminance uniformity and correlated colour temperature on the physiological parameters, only differential effects among the three levels were found.
In this paper, the dimming effects on the photometric and electric characteristics of high intensity discharge lamps supplied by a low frequency square waveform are evaluated. For this evaluation an electronic ballast is presented. The ballast consists of a current source, AC/DC converter and a full-bridge inverter. The electronic supply provides to the lamp a different form of current excitation (square waves with variable short drops). Dimming control and the characteristics of low frequency operated high intensity discharge lamps are described. The lamp is represented in a simulation by its conductance model and coupled to its electronic power supply. Experimental results are shown and compared with the simulation. A dimming range from 100% to about 60% has been achieved.
Pulse width modulation for dimming the light output of LEDs has become common. When pulse width modulation is used at low frequencies unwanted visual artefacts including flicker perception and stroboscopic effects may occur. These artefacts need to be avoided or at least reduced to a minimum in order to obtain high user acceptance. In this paper, an optimized phase-shifted pulse width modulation method is described, implemented and validated in a visual experiment. The method is intended to minimize the stroboscopic effect on a reference surface by first optimizing the LED units of a single LED luminaire and then co-optimizing several of these luminaires. The optimized pulse width modulation waveforms are then compared to standard pulse width modulation dimming methods. In the visual experiment, 13 subjects rated the extent of the stroboscopic effect of standard and optimized waveforms in a white painted experimental room. The results indicate that the optimized waveforms are indistinguishable from constant light.
While the use of satellite weather files is a possibility in regions without terrestrial stations, it is necessary to consider their impact on daylight simulations. This paper aims to verify the variability of dynamic daylight simulation results according to the weather file used. This study compares the results of daylight simulations in learning spaces using different weather files (land-based station data and satellite data). This work is divided into three main stages: comparative analysis of climatic databases; comparative analysis of annual outside horizontal illuminance; analysis of dynamic daylight performance metrics. Annual calculated dynamic daylight metric indicates variations of up to 13% under the different weather files analysed. This is a relevant topic since the accurate prediction of daylight levels for indoor environments guides daylighting design.
The widespread use of self-luminous devices at nighttime (cell-phones, computers, and tablets) raises some reasonable concerns regarding their effects on human physiology. Light at night is a known circadian disruptor, particularly at short visible wavelengths, and it seems advisable to have practical tools for tailoring the spectral radiance of these displays. We analyse two possible strategies to achieve this goal, using hardware filters or software applications. Overall, software applications seem to offer, at the present time, the best trade-offs for controlling the light spectra emitted by existing devices. We submit that such tools should be included as a standard feature on any self-luminous device and that their default settings should be established according to the best available knowledge on the circadian effects of light.
This paper describes two experiments that were designed to investigate the museum lighting environment in terms of correlated colour temperature and illuminance. The results are reported as visual perceptions and perception zone maps. Experiment 1 was conducted to investigate the impact of the illumination conditions on visual perceptions in a light cabinet. Experiment 2 was the same as Experiment 1, except that it was performed in a museum. The rating scores were combined to establish the perception zone maps on a correlated colour temperature–illuminance plane. Furthermore, two emotional response models, named the visibility model and the warmth model, suitable for museum indoor lighting in small- and large-scale spaces were established. The analytical results indicated that the pleasant zone found in this study partially agrees with Kruithof's rule.
This study examines the effect of different types of lamps on pedestrian night time visibility. Detection distance was used as a measure of visibility. The detection distance was measured in the presence and in the absence of on-coming car headlamps in an unlit street. Subsequently, the street was lit using metal halide, high-pressure sodium or LED luminaires. A pedestrian who changed his clothing colour randomly was used as a target. The results showed that the detection distance on the unlit road was 52% shorter in the presence of on coming car headlamps than when the oncoming car headlamps were off. A person wearing black clothing was harder to see and their mean detection distance was 60% less than when the observer was not dazzled by the oncoming car headlights. When the street was lit, the detection distance was doubled. The mean detection distance using LED lamps was statistically similar to that obtained using metal halide lamps, both of which were better than the detection distance obtained under high pressure sodium lighting.
A pedestrian may judge the intentions of another person by their facial expression amongst other cues and aiding such evaluation after dark is one aim of road lighting. Previous studies give mixed conclusions as to whether lamp spectrum affects the ability to make such judgements. An experiment was carried out using conditions better resembling those of pedestrian behaviour, using as targets photographs of actors portraying facial expressions corresponding to the six universally recognised emotions. Responses were sought using a forced-choice procedure, under two types of lamp and with colour and grey scale photographs. Neither lamp type nor image colour was suggested to have a significant effect on the frequency with which the emotion conveyed by facial expression was correctly identified.
The preference for the chromaticity of high illuminance, high colour rendering LED illumination of different scenes was investigated for Chinese and European observers. An experiment about the preference for perceived illumination chromaticity was conducted with the same multi-LED light engine, same viewing booth and same coloured objects transported between Germany and China. Observer preference for perceived illumination chromaticity was significantly influenced by correlated colour temperature (2700 K–6500 K), object scene colour (red, blue or mixed), cultural background (Chinese or European origin, living in Germany or in China) and gender (men, women). The results can be used to choose an appropriate correlated colour temperature (e.g. warm white or cool white) for a high-quality lighting product to illuminate different object scenes (e.g. red or blue objects) so as to achieve good user acceptance in the global market.
The method for evaluating the colour rendering of light-emitting diode sources is controversial, especially for the appearance of human complexions. A psychophysical experiment was conducted using Chinese models to examine the effect of various illumination settings, characterized by two levels of preferred skin colour index and four levels of correlated colour temperature, on preference for the appearance of the Chinese complexion. Results showed that the preferred skin colour index was an effective indicator. Taking incomplete colour adaptation into account, the preferred skin colour index was recalculated and shown to be the best colour rendering index for the appearance of the Chinese complexion. This research examined the concept of preferred skin colour index for Chinese women. This can supplement other colour quality evaluation methods, and shows promise for commercial lighting applications.
Luminous intensity distributions enable an evaluation of the spatial radiation characteristic of a light source. This radiation characteristic is determined by the structural properties of the light source, its operating parameters and the properties of the measuring system. This paper describes some possible methods and rules for comparing luminous intensity distributions. The focus is on the development of calculation rules for quantifying the differences between two luminous intensity distributions. The difference measures developed allow the user to establish an objective comparison between luminous intensity distributions, this comparison being completely independent of the measuring system, the properties of the luminous intensity distributions and the users themselves. Further, the dependence of the properties of luminous intensity distributions resulting from measurement practice, such as adjustment uncertainties, regions that cannot be covered or measured, deviations of the total luminous flux, data noise and resolution differences, are discussed, and appropriate pre-processing and correction steps proposed. In addition, various visualisations of the differences between two luminous intensity distributions are demonstrated and the functionality of the difference measures developed is documented.
In this paper, the design of a luminaire for badminton court illumination is demonstrated from concept through computer simulation, construction trials, on-site installation, comparison with simulations and, finally, evaluations of the illuminated environment before and after the installation of the luminaires. The luminaire is composed of two high-performance light-emitting diode lighting modules, volume scattering diffusers with a one-shot transmittance higher than 70% and a reflecting cavity with a reflectivity higher than 85%. The luminaire has three different exit faces forming three Lambertian-like light sources with low luminance so as to reduce glare to the players when looking at the flight of the shuttlecock. Under similar total electric power consumption, compared to the original traditional lighting, the average illuminance on the ground is enhanced by about 300% and the uniformity is obviously improved. A questionnaire was issued to players before and after the installation of the new light-emitting diode luminaires. The new installation gained much more positive responses for brightness, comfort and number of usable courts from the players than the old installation.
Numerous efforts have been made to investigate how to characterize the effect of light sources on colour preference. This paper describes a psychophysical experiment to compare the colour preference evaluation among three sources for different lighting applications. Three lighting applications – restaurant, retail display, and supermarket – were created in two side-by-side full-scaled rooms. It was found that the colour preference varied with the lighting applications. Although none of the existing single-value measures can predict the preference for all three applications, a single measure is necessary for general consumer use given a careful definition of general lighting. In addition, lighting application specific measures could be useful for lighting professionals and experts. To provide detailed information, a colour distortion icon, with improved test colour samples will be useful.
Light emitting diodes with high colour quality were investigated to enhance colour appearance and improve observers' preference for the illuminated objects. The spectral power distributions of the light emitting diodes were optimised by changing the ratios of the narrow band red, green and blue light emitting diodes, and the phosphor-converted broad-band light emitting diode to get the desired colour rendering index and high gamut area index. The influence of the light emitting diode light on different coloured fabrics was investigated. The experimental results and the statistical analysis show that by optimising the red, green, blue components the light emitting diode light can affect the colour appearance of the illuminated fabrics positively and make the fabrics appear more vivid and saturated due to the high gamut area index. Observers indicate a high preference for the colours whose saturations are enhanced. The results reveal that the colour-enhanced light emitting diode light source can better highlight products and improve visual impression over the ceramic metal halide lamp and the phosphor-converted light emitting diode light source.
While UK governments have recently sought to increase cycling activity, it remains a minority interest. One reason for this is the perceived danger of cycling on roads filled with traffic. There is statistical evidence to support this perception; for equal exposure, cyclists are more likely to be seriously injured than either drivers or pedestrians. Lighting has a role to play in reducing the hazards of cycling by enhancing the visibility and conspicuity of cyclists. Unfortunately, it is not at all clear that the current lighting regulations and recommendations for cycling and cyclists are the best that can be achieved or are even adequate for these purposes. A number of actions are suggested that should enable lighting’s contribution to the safety of cyclists to be realized.
Methods to increase the efficiency of a rare gas–water vapour plasma as a light source are presented: (1) the addition of a second rare gas (2) the use of titanium dioxide to enhance the decomposition of water molecules into hydroxyl and hydrogen; (3) pulse discharge operation to improve the efficiency. Analysis shows that the first two methods can yield an increase in efficiency. Use of the catalyst produced a tangible impact on plasma properties and an increase in efficiency that was experimentally observed and agrees with theoretical estimates. In pulse discharge operation, negative ions that are probably created in the afterglow phase eliminate the desired effect. The data obtained using these three approaches, point towards possible directions for further investigation and predict the expected results in case of successful implementation.
A white LED complemented by cyan and red LEDs is a good candidate for achieving high colour rendering at low correlated colour temperatures. This is usually very difficult with commercially available white LEDs. In addition, the system is able to replace incandescent lighting in many applications; for example, the lighting for museum display cases. To investigate and optimize the colour and light distribution properties, both spectral and geometrical modelling are used. Mapping of the possible combinations of LEDs is used to locate the optimal solutions within the colour gamut, with emphasis on chromaticity and colour rendering indices. A geometric optical model is used to design and optimize the homogeneity of the colour and light intensity distribution as a function of angle. The resulting system produces diffused homogeneous white light with a tunable correlated colour temperature from 2000 K to 2400 K. Within this range the white light is characterized by a high general colour rendering index (Ra > 90), special colour rendering indices for saturated red objects (R9 > 85), and low chromaticity distance (Duv) from the Planckian locus (Duv < 2 x 10–3).
This study investigated the discomfort glare caused by LED luminaires. It included three different LED luminaire structures, under two background luminances, seen at two different angles above the line of sight. Observers scaled glare using a seven-category scale. The results showed that a darker background or a smaller angle led to more discomfort glare and a non-uniform luminaire produced more glare than a uniform one. Furthermore, Unified Glare Rating was tested using the data. It performed reasonably well, but there is still room to improve the predictions for non-uniform LED luminaires.
This paper investigates the interaction between retail lighting and textiles to provide retailers and lighting designers with a set of physical textile objects that can be used to test the visual effect of a lighting setting. Since the relationships between optical aspects of lighting–textiles interactions and subjective qualities associated with them have not been systematically investigated, we conducted two experiments to study those relationships. The first experiment concerned photometric measurements of textiles in order to categorize the reflectance types. The second experiment examined human observers’ judgments of a range of material-expressing qualities, such as shininess and softness, in two canonical types of lighting. The textiles for which the differences in those qualities were maximal were used in designing a lighting probe set.
Obstacle detection is an important visual task for pedestrians. An experiment was carried out to measure the ability to detect peripheral obstacles under variations of illuminance and scotopic/photopic luminance ratio and with older and younger test participants. The LED array used in this work enabled scotopic/photopic ratio to be varied whilst chromaticity was held constant. The tests employed a full-scale model with dynamic fixation and walking to better simulate pedestrian experience than in past work. Detection performance increased with illuminance, reaching a plateau at 2.0 lux. A higher scotopic/photopic ratio improved obstacle detection but only at the lowest illuminance used in this study (0.2 lux). Older participants showed poorer obstacle detection performance than younger participants but again only at the lowest illuminance.
This paper presents a pilot study that investigated the suitability of mean room surface exitance as a predictor of spatial brightness and perceived adequacy of illumination, and then compared these results with how horizontal illuminance predicted both items under the same conditions. The experiment included 26 participants. A small office was used for the study. It exposed participants to three levels of mean room surface exitance, each delivered with three different light distributions and across three different surface reflectances, resulting in a total of 27 light scenes. A clear relationship existed between mean room surface exitance and both perceived adequacy of illumination and spatial brightness, but not between horizontal illuminance and either item. Correlations were drawn between reported levels of spatial brightness and reported levels of perceived adequacy of illumination.
Five different types of LED lamps were aged for 35 months at room temperature and for six months at the temperatures of 45℃ and 60℃. The lifetimes for the lamps were predicted from the luminous flux measurement results. The long-term tests show that early predictions of lifetime can be pessimistic. The results at higher temperatures show that ageing can be accelerated by modest heating. On the average, heating to 45℃ reduced the lifetime by a factor of 1.35 and heating to 60℃ by a factor of 2.36. An alternative accelerated method to test and analyse ageing is proposed. During the ageing of 35 months, the changes in correlated colour temperatures were smaller than 4.3%.
Providing subjective impressions of security is central to outdoor lighting design. Current parking lot lighting recommendations are based upon photopic illuminances, regardless of spectrum. Scene brightness perception is directly related to impressions of security, and depends upon both light level and spectrum. A provisional model was used to predict scene brightness for three parking lots, each illuminated to different levels by different light sources. Observers judged scene brightness, security and other factors for each lot. The provisional model accurately predicted both scene brightness and security judgements. The lighting associated with the best subjective ratings also had the lowest power density. A design method using ‘brightness illuminance’ is presented, which can lower system costs while maintaining a sense of security by users.
We tested the hypothesis that the phototatic response of nocturnal insects is influenced by the flickering of light sources by comparing the numbers of insects captured in traps illuminated with flickering and non-flickering light. Four flicker profiles produced by a square pulse wave with different combinations of frequency and duty cycle were investigated. Overall, fewer insects were captured in traps illuminated with a flickering light source, independent of the flicker setting used. Furthermore, the difference observed was statistically significant for specific combinations of flickering conditions and insect orders, thus suggesting that flickering reduces the number of nocturnal insects attracted to light sources.
This paper describes two human factors experiments designed to assess the influence of flicker characteristics on the perception of stroboscopic effects from flickering light. Specifically, the following factors were investigated: temporal waveform shape, frequency, duty cycle, percent flicker and flicker index. For a given frequency, the flicker index appears to be more predictive of the detection and acceptability of stroboscopic effects than the percent flicker value.
The International Commission on Illumination (CIE) has published a recommended system for mesopic photometry based on visual performance. The system provides means for determining mesopic photometric values based on measuring the spectral composition and intensity of light. The system uses an iterative calculation method. We investigate the conditions under which this system is applicable and identify potential problems with the iterative method. We show that the system works well for the vast majority of lighting applications. However, it has non-convergence and discontinuity issues for sources with very high and very low values of scotopic-photopic ratio. A set of parameterised formulae is presented that approximates the mesopic model and provides a continuous, closed-form solution for the adaptation level in all lighting conditions.
A digital circuit for driving a low-frequency, small-wattage, high-intensity discharge lamp is proposed. By combining a digital potentiometer X9313 and a microcontroller STM32F103, the lamp can be turned on and off automatically according to the operating condition. The lamp power can be altered flexibly based on the needed luminance because it is designed to be a linear function of the resistance of the potentiometer X9313. The lighting system has an electrical efficiency of 88% and can save more than 20% of energy, compared with a traditional lamp. A remote desktop client on Android is developed for the purpose of wireless and convenient control. The proposed model will provide important information for designing high-performance, low-frequency, small-wattage, high-intensity discharge lamps.
This paper presents a pilot study that has investigated the suitability of mean room surface exitance as a predictor of spatial brightness and compared these results with how horizontal illuminance predicts spatial brightness under the same conditions. The experiment took a group of 26 participants and, using a scaled booth, exposed each participant to three levels of mean room surface exitance, each delivered with three different light distributions and three different surface reflectances, resulting in a total of 27 light scenes. Results demonstrated that, under the range of conditions to which participants were exposed, a systematic relationship existed between mean room surface exitance and spatial brightness, but not between horizontal illuminance and spatial brightness.
In this paper, we analyse theoretically and numerically the sky glow in urban and suburban areas, focusing on the zenith-normalised luminance of a cloudy sky. The results suggest that the altitude of a cloud imposes important changes in the luminance distribution. Peak values of sky luminance can be observed at a distance
Results from a mesopic threshold detection experiment using static, quasi-monochromatic, 2° incremental detection targets were used to test the International Commission on Illumination (CIE) recommended system for mesopic photometry based on visual performance. An experimental apparatus was built to produce different mesopic backgrounds (four different spectral compositions at two different luminances, 0.1 cd/m2 and 1.0 cd/m2) on which the targets were projected at different eccentricities (2.65° and 10°). The CIE system was tested by two methods, variability of mesopic threshold contrast for different target chromaticities and trend analysis for mesopic threshold contrast plotted against background mesopic luminance. The mesopic threshold contrast did not remain constant among the different target centroid wavelengths within a given viewing condition. The inter-observer variability of the mesopic contrast threshold dataset was considerable.
This paper reports the results of measurements performed in a test room to investigate the impact of using different wall colours and light scenes on indoor lighting quality. Eye level spectral irradiances were measured for a user located inside the room and seated at a desk. These measurements allow the use of the Irradiance Toolbox, which makes it possible to calculate equivalent illuminances for the photopigments in the human eye. Moreover, the CIECAM02 colour appearance model was used to investigate the variations in hue and chroma values of the different wall colours when changing the light scene. The results demonstrate that there are significant variations in eye level spectral irradiance distributions, photoreceptor stimulation and hue and chroma values with different combinations of wall colours and light scenes.
This paper discusses the performance evaluation of anidolic concentrators in an overcast sky condition. The concentrators were designed, with acceptance angles of 60°, 70° and 80°, first by maintaining the profile of the concentrator’s uniform and secondly by keeping the height uniform. Studies were done using these concentrators with a model light pipe and the performance was compared with that of an acrylic dome and a profiled Fresnel collector. For a given condition, the illuminance ratio (ratio of illuminance measured at the base of the pipe to external illumination) increased with the acceptance angle. For a given acceptance angle, the concentrator with uniform height and variation of entrance aperture, performed better than a concentrator having a uniform profile.
Light emitting diodes, with advantages in energy savings, luminous efficacy and greater reliability, are becoming preferred over conventional white light sources. Currently, only light output depreciation is considered for life estimation of light emitting diode luminaires but it is recommended to include colour shift variations for applications demanding colour stability. In this paper, an extended Kalman filter is employed to determine L70 life and colour temperature degradation over life of a light emitting diode luminaire. The colour shift in terms of Duv is determined by statistical polynomial cure fitting. The variation in chromaticity coordinates over life is determined and life based on colour shift is determined by acceptable Duv limits. The results are compared to life determined by the IES-TM-21 method and the correlated colour temperature limits taken from the luminaire data sheet.
Light is the major synchronizer of circadian rhythms to the 24-hour solar day. Compared to the visual system, the circadian system requires more light to be activated and is more sensitive to short-wavelength light. Without access to daylight, or electric lighting providing a comparable amount, spectrum, distribution, duration, and timing, human health and well-being may be compromised. This may be particularly true for those confined indoors, such as patients in hospitals and residents in care facilities. Architectural and design features, including window size, surface reflectances, and furniture placement, impact circadian stimulus levels. This paper details results of simulations used to determine the percentage of days that patients would receive a minimum level of circadian stimulation as a function of different window-to-facade ratios, surface reflectances, and latitudes.
In this paper, an LED downlight producing dynamic beam variation without any mechanically moving parts is presented. The functionality is based on an optics design using compound parabolic concentrators equipped with individual LEDs. With suitable driving of the LEDs, a dynamic far-field beam with an adjustment range of between 16° and 55° is achieved. The luminaire is used as a demonstration of the polyurethane vacuum casting rapid manufacturing method to produce low-cost freeform optics for prototypes. The simulations and measurements on the realized prototype show that the method is suitable for small series and prototype manufacturing, but also reveal potential errors in the rapid manufacturing process to be avoided in the future.
This study set out to understand the benefits of improved illuminance uniformity in parking lots in terms of user perception and acceptability, as well as energy use, and to demonstrate that light-emitting diodes (LEDs) can achieve uniform distributions more efficiently than traditional light sources. The results from a field evaluation showed that more uniform illuminance distributions are favourably perceived by people in terms of goodness of illumination, ability to see around and at a distance, and perception of safety – all of this at a much lower average horizontal illuminance. Thus, improving uniformity alone can translate into lower energy use and potential for less glare and light pollution. Optical modelling showed that LEDs have a much greater potential to efficiently produce uniform illuminance distributions than larger light sources such as high pressure sodium or metal halide.
A practical method is proposed for the design of a freeform reflector for light-emitting diode low-beam headlamps. The energy relationship between the solid angle of the light-emitting diode source and the target plane is first established. A freeform reflector is then constructed based on Snell's Law and the light energy redistribution maps are obtained by optimising meshing parameters on the target plane. By using this method, four reflectors are designed to constitute a module for the low-beam headlamp, and three different types of light-emitting diode sources are selected for simulation. Results demonstrate that the best light pattern can be obtained with the LUW HWQP light-emitting diode source whose chip size is 1.0 mmx1.0 mm, and the lighting distribution can fully satisfy the requirements of the ECE R112 regulations without any other lenses, shields or baffles. Furthermore, the optical efficiency can reach up to 79%.
This paper studies spectrum optimization of four-package LEDs to improve performance of light sources with respect to properties such as luminous efficacy and colour rendering as well as luminous efficacy of radiation under photopic and mesopic conditions and circadian efficacy of radiation for non-visual biological effects. For colour mixing of four-package LEDs, the proportion of each LED in the package follows a linear relationship as does luminous efficacy. For optimization of luminous efficacy of radiation and circadian efficacy of radiation, an inverse proportion function model is proposed. An example of spectrum optimization for a four-package LED shows that by using the proposed model, high performance can be achieved with different weighting coefficients for different applications.
We consider a smart lighting control system for daylight and occupancy adaptation with illumination and dimming constraints. The lighting system has multiple luminaires, with co-located light and occupancy sensors, and a central controller. The sensors communicate local occupancy state and illuminance measurements to the central controller where dimming levels for the luminaires are optimized. We consider an optimization framework wherein the objective is to minimize the power consumption subject to illumination and dimming constraints. The illumination constraint is to achieve an illumination value at the light sensor that is above a specified set-point, depending on the occupancy state. The dimming constraints are to achieve a level of spatial uniformity in dimming levels of the luminaires within a neighbourhood, with the dimming levels being within physical limits. We propose an iterative method for optimization to determine the dimming levels that (i) does not require explicit daylight knowledge for every iteration, and (ii) induces smoother dimming level changes in luminaires. The proposed method and optimization framework is compared with existing approaches, in terms of achieved illumination and dimming values, in an open-plan office lighting model.
Self-luminous devices, such as computers, tablets and cell phones can emit short-wavelength (blue) light, which maximally suppresses melatonin. Melatonin is a hormone that starts rising approximately 2 hours prior to natural bedtimes and signals darkness and sleep to the body. The present study extends from previously published studies showing that light from self-luminous devices suppresses melatonin and delays sleep. This is the first study conducted in the home environment that investigated the effects of self-luminous devices on melatonin levels in adolescents (age 15–17 years). Results show that 1-hour and 2-hour exposure to light from self-luminous devices significantly suppressed melatonin by approximately 23% and 38% respectively. Compared to our previous studies, these results suggest that adolescents may be more sensitive to light than other populations.
A metric is proposed for predicting the perception of light source flicker from a measurement of the relative light output waveform. The metric is the weighted quadrature sum of the temporal spectral components comprising the waveform after dividing by the waveform mean. The metric’s foundation is that used by the IEC flickermeter, which assumes a linear, time invariant human response to flicker. This assumption, restated in terms of the spectral components being additive and independent, was found to accurately model the flicker detection thresholds for a range of waveform shapes and frequencies. In the testing of the additive and independence requirements, the empirical spectral sensitivity to flicker was measured for 10 observers. The metric also correctly predicted whether flicker was detected for five commercial A-lamps.
Using road lighting to improve the detection of potential hazards may contribute to reduced accident rates for pedestrians, drivers and other road users. In past studies carried out to measure peripheral detection, the test participant was instructed to maintain fixation on a target during presentation of the peripheral target, but these studies did not question the degree to which this fixation was maintained. We therefore used eye tracking to record fixations during a peripheral detection task and introduced a fixation task designed to encourage fixation. It was found that observers were good at maintaining foveal fixation and there was little benefit in introducing a fixation task although this might be of greater benefit if the peripheral field contains more interesting distractions.
In this work, we propose an approach to estimating the amount of light wasted by being sent towards the upper hemisphere from urban areas. This is a source of light pollution. The approach is based on a predictive model that provides the fraction of light directed skywards in terms of a small set of identified explanatory variables that characterise the urban landscape and its light sources. The model, built via the statistical analysis of a wide sample of basic urban scenarios to compute accurately the amount of light wasted at each of them, establishes an optimal linear regression function that relates the fraction of wasted flux to relevant variables like the kind of luminaires, the street fill factor, the street width, the building and luminaire heights and the walls and pavement reflectances. We applied this model to evaluate the changes in emissions produced at two urban nuclei in the Deltebre municipality of Catalonia. The results agree reasonably well with those deduced from the radiance measurements made with the VIIRS instrument onboard the Suomi-NPP Earth orbiting satellite.
It is important to be able to engineer the brightness of interior spaces. In addition to the amount of light delivered to and reflected from surfaces in the space, light spectrum influences apparent scene brightness. Specifically, spaces illuminated by ‘cool white’ sources will look brighter than those illuminated by ‘warm white’ sources for the same photopic light levels. A scale model residential space was used to obtain judgements of scene brightness where light levels, surface reflectances and light source correlated colour temperatures were parametrically varied. Subjective and radiometric data were used to extend a provisional model of scene brightness, which is intended to be useful for predicting scene brightness of interior spaces illuminated to different levels by ‘white’ light sources of different correlated colour temperatures.
This paper presents a systematic material selection process for technical, environmental and economic criteria. This methodology has been applied to the design of a weatherproof luminaire. The materials selected for the production of this diffuser were characterised to obtain their mechanical properties and to perform exhaustive research on impact analysis by means of finite element modelling. Also an economic analysis and an ecological impact assessment have been performed. Thanks to this working methodology, a final design of the diffuser has been developed having the optimum thickness to achieve the mechanical specifications and minimise the environmental impact and the cost of the diffuser.
The life of light-emitting diodes (LEDs) is difficult to measure by traditional testing methods as they are not likely to fail completely. The Illuminating Engineering Society of North America (IESNA) uses a standard regression approach based on short-term collected lumen data to predict the L70 lifetime of LEDs. In this paper, a model-based prognostics method is employed to determine the life of luminaires using LEDs. Unscented Kalman filter and particle filter algorithms are used for degradation model parameter estimation. An analytical approach based on three statistical models (Weibull, normal, lognormal) is employed and a best fit is determined by the Akaike information criterion. The resulting L70 is compared with L70 derived from the IESNA approach to accurately determine the best prognostic method.
This paper aims to identify suitable and energy-efficient luminous environments for two users sharing the same office and conducting various activities at the same time (paper and/or computer-based work, meeting with a visitor). The office is lit by daylight, controlled by an exterior shading system and by artificial light, composed of ceiling sources and a task lamp on each desk. In all, 930 subjects participated in six psychophysical tests conducted on the internet, each dedicated to a user position and an activity. Multiobjective optimizations were then performed with the collected data in order to identify luminous environments that realized the best tradeoffs between visual conditions for both users and power demand. An optimized luminous environment, judged suitable, whatever the combinations of activities in the room, is proposed.
An artificial skylight has been developed which aims at creating an impression of a daylight opening in the ceiling by means of an artificial sunspot and a blue sky with perceived infinite depth. It is the goal of this work to compare and quantify the perceived room atmosphere created by this artificial system with that created by a conventional lighting system. A total of 100 subjects participated in a randomized controlled study within which the short-term effects on room lighting- and room atmosphere-appearance were determined. Both the artificial skylight and the resulting room atmosphere were perceived as very natural and attractive. Thus, the first strong evidence for the expected positive effects of this artificial skylight was determined.
This study investigated the main visual perceptions and the optimal LED lighting parameters for viewing museum paintings. Oil and gouache paintings seen under different LED illuminants were assessed using the categorical judgement method. It was found that ‘visibility’ and ‘warmth’ are the main perceptions for viewing paintings. The results showed that a correlated colour temperature around 3500 K, a negative deviation of the target from the blackbody locus and a high colour rendering index can achieve satisfactory results. The difference between colour fidelity-based colour rendering indices and colour preference-based colour rendering indices for a museum application was also explored.
Previous laboratory experiments have provided evidence of an effect of time of day on glare sensation. During the tests, temporal variables and personal factors were also measured to analyse their influence on levels of visual discomfort as the day progresses. The results revealed statistically significant and practically relevant tendencies towards greater tolerance to source luminance from artificial lighting at all times of day for earlier chronotypes and for participants not having ingested caffeine. No conclusive evidence was found for the effect of fatigue, sky condition and prior light exposure on glare sensation throughout the day. These findings suggest that temporal variables and personal factors should be measured in conjunction with visual discomfort levels to explore the causes of the wide individual differences commonly associated with the subjective evaluation of glare sensation.
We propose a freeform reflector for light-emitting diode bicycle head lamps based on a feedback method. The energy relationship between the solid angle of the light-emitting diode source and the target plane is first established. A reflector is then constructed based on non-imaging optics theory and Snell’s Law. Feedback modifications are applied in accordance with the deviation between the simulated and the desired light distribution. Then the reflector is regenerated and the deviation is minimized after several iterations. A reflector for a bicycle head lamp is designed for the Cree XP-E LED source whose emitting surface is 1.2 mm x 1.2 mm. Simulation results indicate that the light performance can meet the K-mark regulations. The optical utilization factor can be improved from 73% to 80% and the illuminance uniformity is improved by 22%.
High-power LEDs with high luminous efficacies, compact sizes, long lifetimes and a wide colour range, are rapidly taking the place of conventional light sources in general lighting applications. But these properties of high-power LEDs are dependent on temperature and driving current. In this study, 24 samples of commercially available, high-power, white LEDs were measurement for their electrical, optical and thermal characteristics as well as their efficiency, luminous flux, luminous efficacy, correlated colour temperature and colour rendering index over six temperature steps at three different driving currents. LED manufacturers' catalogues including such information will allow consistency between the design and application stages of an installation. Also, it will make the technical and economic optimization of luminaires using high-power LEDs easier.
A study of scene brightness perception was conducted to assess whether spectral sensitivity for scene brightness perception at low to moderate light levels (~3–110 lux) could be partially explained by a contribution of intrinsically photosensitive retinal ganglion cells (ipRGC). An experiment was conducted at two different light level ranges and using two different spectral power distributions. The results suggest an increase in short-wavelength spectral sensitivity as a function of increasing light level. The results also confirm that including ipRGC as well as cone photoreceptor input in scene brightness spectral sensitivity resulted in improved predictions compared to including either cone input only or rod as well as cone input.
A half-bridge circuit topology for driving high-intensity discharge lamps at high frequencies is proposed. The high-frequency square wave is modulated synchronously by low-frequency, sawtooth signals. Under such circumstances, the phenomenon of acoustic resonance can be successfully prevented because standing waves within the wall of the lamp are eliminated. This has been experimentally verified. Results obtained will offer useful information for designing high-efficiency high-intensity discharge lamps.
Solar reflections from buildings can cause veiling glare, which reduces visibility and may increase the risk of traffic accidents. A veiling glare assessment typically includes two steps. Firstly, identifying the number of reflections that are geometrically possible, and secondly, quantifying if these reflections are sufficiently intense as to cause glare. Current methods of assessment address the first step but become laborious when calculating the intensity of the reflections. This is due to the geometrical complexity and the potential number of reflections. The new method presented in this paper demonstrates greater simplicity than previous approaches whilst providing a clearer graphical output with the aid of ray-tracing software.
The average daylight factor is one of the most widely used methods for predicting the internal illuminance due to daylight. It is a simple tool that can be used in the early stages of design and can give information about the luminous environment inside a room. This method is supposed to be used under overcast sky conditions. Expanding the use of the average daylight factor to other sky conditions will encourage the use of daylight in buildings. Several methods have been proposed for the prediction of daylight based on the CIE Standard General Sky. However, most of these methods aimed for a detailed estimation of the internal illuminance pattern. This paper aims to investigate the potential for using the average daylight factor method under the ISO/CIE Standard General Sky.
Three perception experiments were conducted to develop a measure for predicting the visibility of the stroboscopic effect occurring in temporally modulated light systems. In the first experiment, different methodologies were evaluated for their measurement error. In the second experiment, the visibilities of the stroboscopic effect for square wave and sine wave light modulations were measured and the results were found to be consistent with previous findings for flicker perception. In the third experiment, specifically crafted, complex waveforms were used to test the theory of frequency summation. Based on the results of these three experiments, a new measure for the visibility of the stroboscopic effect was developed, consisting of a summation of the energy in all frequency components, normalized for human sensitivity.
Road lighting in residential roads should enhance the visual component of interpersonal judgements concerning the apparent intent of other pedestrians – whether friendly, aggressive or indifferent. This paper describes an experiment which collected forced-choice judgements of emotion and gaze direction after 1000 ms exposure under 18 combinations of lamp type, luminance and interpersonal distances. Better performance was found with higher luminance and larger task size, but with diminishing returns according to a plateau-escarpment relationship. The results were used to estimate appropriate light levels for outdoor lighting. Results for judgements of emotion from facial expression suggest a minimum luminance of the face of 0.1–1.0 cd/m2 if facial expressions are to be identified accurately at 4 m, but a luminance above 1.0 cd/m2 for identification at 10 m.
Light sources are available in a variety of spectral power distributions (SPDs) and this affects spatial brightness in a manner not predicted by quantities such as illuminance. Tuning light source SPD to better match the sensitivity of visual perception may allow the same spatial brightness but at lower illuminance with potential reductions in energy consumption. Consideration of experimental design was used to review 70 studies of spatial brightness. Of these, the 19 studies considered to provide credible evidence of SPD effects were used to explore metrics for predicting the effect of SPD but did not provide conclusive evidence of a suitable metric, in part because of incomplete reporting of SPD characteristics. For future work, these data provide an independent database for validating proposed metrics.
This paper investigates the critical visual tasks of pedestrians, the first step in a review of design guidance for lighting in residential roads. Eye tracking was used to record pedestrians’ visual fixations when walking outdoors in daytime and after dark with a concurrent dual task to better understand which fixations were critical. Fixations at critical instances, these being shown by slow reactions to the secondary task, were categorised into one of eight groups. Of these, the path and other people were the most frequent items, with people more likely to be fixated at a far distance and the path at a near distance. After dark the path was more likely to be fixated and other people less likely to be fixated compared with daylight.
This article investigates different approaches to the interpretation of eye-tracking video records of pedestrians walking outdoors to determine the apparent importance of fixation on other pedestrians and how this is influenced by the frequency of occurrence. The three approaches were as follows: the proportion of time that fixations were on pedestrians (14%), a common approach to interpretation; the proportion of fixations at critical moments that were on pedestrians (23%), critical moments being defined by a delayed response to a dual task; and the probability of an approaching pedestrian being fixated at least once (86%). These data were compared against the number of pedestrians encountered during the trials; the proportion of all fixations and the probability of fixating people were affected by the number of people encountered – only the critical-fixations data did not exhibit a trend.
This paper concerns road lighting for pedestrians and how this aids reassurance, their confidence when walking alone after dark. Evidence from past studies that lighting enhances reassurance is supported by the findings of an unfocussed approach that aimed deliberately to avoid focus on lighting or fear, thus to counter the unintended potential for focussed, quantitative methods to lead towards such a finding. Review of the characteristics of lighting suggests an optimum illuminance of 10 lux, of high S/P ratio, and aimed toward the pedestrian and natural elements of the environment, will enhance reassurance. Further research is needed to validate the optimum illuminance, the appropriate metric for characterising lamp spectral power distribution, and the most desirable aims of spatial distribution.
After dark, road lighting should enhance the visual component of pedestrians’ interpersonal judgements such as evaluating the intent of others. Investigation of lighting effects requires better understanding of the nature of this task as expressed by the typical distance at which the judgement is made (and hence visual size) and the duration of observation, which in past studies have been arbitrary. Better understanding will help with interpretation of the significance of lighting characteristics such as illuminance and light spectrum. Conclusions of comfort distance in past studies are not consistent and hence this article presents new data determined using eye-tracking. We propose that further work on interpersonal judgements should examine the effects of lighting at a distance of 15 m with an observation duration of 500 ms.
Sky-luminance distribution is the basic requirement for daylighting calculations and design. It is also important for describing and defining the different sky types. However, owing to the lack of test equipment and measurement data, research on sky-luminance distribution in China has been limited. Therefore, for the first time, we have obtained the sky-luminance distribution data using our self-developed spectrum sky scanner from observations over 12 months. Furthermore, we have established a relationship between the actual sky types of Beijing and the Commission Internationale de l'Eclairage standard sky model. These data are very important in the study of the daylight climate of China.
This study examined the impact of light source (LED and HID) and correlated colour temperature (warm-white and neutral-white) on the well-being, mental state and concentration of shop assistants. The experimental design was a 2 x 2 design with repeated measures and complete permutation on all factor combinations with 48 participating shop assistants. Results showed effects of the colour temperature on the well-being and mental state of the shop assistants. No effects of light source could be found for the explored variables. Warm-white colour temperature positively affects the intensity of well-being and mental state and negatively affects the power of concentration.
Quantitative relations between discomfort glare evaluation and photometric quantities such as illuminance at the observer’s eye, average luminance of the source area, average luminance of the effective area and effective glare luminance for white LED sources having a variety of spatial luminance distributions have been investigated. Effective glare luminance, which is the sum of luminances in the luminaire area divided by the effective area, explains the scaling results of all sources in the same way. In addition, a new equation modified from the Commission Internationale de l'Éclairage Unified Glare Rating formula using the effective glare luminance showed a strong correlation with the scaling results. It is thus suggested that effective glare luminance is a useful index of discomfort glare for light sources having different spatial luminance distributions.
An effective high-efficiency LED headlamp system for automotive low-beam lighting which consists of parabolic reflector, compound lenses and combined prisms, is introduced in this paper. Using a single, high-brightness LED, the illumination requirements for a headlamp low beam specified by UNECE regulation ‘Addendum 111: Regulation No. 112 Revision 2’ can be achieved. On the test screen at a distance of 25 m, simulation results as well as testing results for the prototype meet the requirements of the UNECE regulation for all specified regions and key points.
Lighting conditions in workplaces contribute to a variety of factors related to work satisfaction, productivity and well-being. We tested whether different photometric variables also influence visual perception and the comfort of the lighting, as well as subjective non-visual variables such as mood, alertness and well-being. Twenty-five young subjects spent two afternoons either under electric light or daylighting conditions (without view from the window). Subjects overall preferred the daylighting for visual acceptance and glare. Changes of photometric variables modulated changes in visual light perception, alertness and mood in the course of the afternoon. Finally, we found several associations of visual and non-visual functions, indicating a potential relationship of visual comfort with other circadian and wake-dependent functions in humans, which consequently could impact office lighting scenarios in the future.
We consider a smart lighting system with multiple dual-beam luminaires, with co-located occupancy and light sensors. A dual-beam luminaire emits a hollow beam and a narrow beam, suitable, respectively, for providing ambient and task lighting both controllable independently. We consider an occupancy- and daylight-adaptive lighting system, wherein the luminaire controller determines the dimming levels of the dual beams such that the lighting system provides a desired illuminance based on local occupancy and light sensor inputs. We present a method for calibrating the light sensors to obtain control set-points and a controller design so that the set-points may be attained. The proposed system performance is compared with a standard-beam lighting system using lighting simulations. We find that the dual-beam lighting system provides higher illumination and power saving in comparison to the standard-beam lighting system, given the additional degree of freedom provided by the two optical beams.
We determined the visual efficiency and visual discomfort for users of a typical transitional space in luminous climates. The subject moves from a brighter exterior to a dimmer interior, facing an abrupt change in the level of lighting as a potential functional vision barrier, mainly for ageing people. We measured suprathreshold visual efficiency in different age groups, recognising two Landolt ring orientations and answering some visual discomfort questions. Results show: oldest group (60–67) needed more than 3 times the time required by the youngest group (25–30) to perform the task but, in terms of discomfort, there are no noticeable effects regarding the disturbance or the sensation of reduction of mobility produced by the lighting changes in the transitional space among the three different groups.
In lighting calculations and simulations, the emission of a light source is conventionally modeled using the far-field luminous intensity distribution. However, the advent of luminaires including large arrays of LEDs with focusing optics creating narrow beams has made the traditional limiting photometric distance to reach far-field conditions less easy to determine. Furthermore, even correct far-field data can lead to erroneous predictions when illuminances are determined on a task surface which is positioned within the near-field region. A near-field representation could overcome these problems, but experimental validation for such LED arrays is lacking. This paper reports on near-field and far-field laboratory experiments using an array of two and five narrow-beam LEDs. A near-field approach makes discussions to determine the far-field photometric distance superfluous and leads to correct illuminances at any location with respect to the array, irrespective of the dimensions of the array and the beam angle of the individual components. Introducing the near-field representation of light sources in lighting design offers more accurate predictions when luminaires based on LED arrays with focusing optics are involved.
An experiment has been carried out to investigate the effect of lighting on the perception of atmosphere in a living room, using three types of light sources: halogen, fluorescent and LED lamps. In a psychophysical experiment, 29 native Chinese observers assessed eight lighting conditions having different luminances and correlated colour temperatures. For each condition, 71 scales were employed using the categorical judgment method. Factor analysis identified two underlying dimensions: liveliness and cosiness. This agrees with those found by Vogels who used Dutch observers to assess atmosphere perception. Both observer groups also agreed that an increase of luminance would make the room more lively. However, there were also some disagreements such as a higher CCT source would make the room more lively for Chinese observers but less lively for Dutch observers.
The implicit homology between light, lighting and neuroscience limits international commerce, the effectiveness of lighting applications and the relevance of basic and applied research. A comprehensive system where the distinct, but interrelated roles of light, lighting and neuroscience are recognized provides a meaningful foundation for international commerce, for improving the value of lighting for society and the environment, and enriching the neuroscience research agenda. By replacing V() with a broader luminous efficiency function, termed the universal luminous efficiency function [U()], light is better defined. By formally accepting a set of benefit efficiency functions for use in lighting regulations and lighting practice, the value of lighting applications increases. By formally accepting a set of benefit efficiency functions in standards and applications, a platform for collaboration among lighting practitioners and neuroscientists is built.
CIE Publication 115 and ANSI/IESNA Recommended Practice 8-00 both use vertical illuminance 1.5 m above the ground as a design criterion for the lighting of pedestrians. While vertical illuminance has the advantage of being easy to calculate and measure, visibility is based primarily on target contrast. A central question related to the visibility of pedestrians is whether drivers need to see the whole pedestrian or can they infer the presence of a pedestrian by recognizing any part of the pedestrian’s shape. The objective of this work was to first explore various pedestrian contrast profiles that could exist and then to find a simplified approach to characterize pedestrian night-time visibility. The problem was addressed through theoretical analyses and computer simulations. Pedestrian contrast was found to be bipolar and dynamic. From the contrast profiles, we developed the concept of dominant contrast, which is defined as the contrast of any part of the pedestrian that provides the highest visibility. Dominant contrast was examined as a metric for street lighting design and night time visibility for (a) an unlit street with car headlights, (b) a lit street without car headlights and (c) a lit street with car headlights. Dominant contrast was found to be a viable metric for street lighting design and night time visibility studies.
Disability glare is associated with veiling luminance caused by light from bright sources being scattered within the eyes of observers, thereby reducing retinal luminance contrast. This study compares the reduction in observers’ performance in the presence of glare with veiling luminance in the eye, calculated using a non-subjective method. A total of 42 observers performed a target detection task in the presence of a glare source in conditions similar to street lighting at night. Luminance contrast thresholds were measured for each observer under different levels of glare. Results show that, while veiling luminance has a significant effect on the performance of observers, its effect is lower than expected from contrast loss. Furthermore, the performance of observers over the age of 50 is unaffected by increasing the glare level.
Many species of insects display a disposition to move towards light. As a consequence, nocturnal artificial lighting often contributes to an increase in insect population among humans. We tested the hypothesis that residential white lamps can evoke significantly different attraction to insects even when their light outputs are nearly indistinguishable to humans. In a two-choice experiment using insect traps equipped with either a compact fluorescent or a LED light source with similar photometric specifications, about three times more insects were captured in the trap with a compact fluorescent lamp than in the LED trap. The results suggest that LED lamps are preferable to compact fluorescent lamps when the objective is to avoid attracting nocturnal insects to households.
In the process of lighting design, usually many lighting alternatives are assessed against criteria such as energy consumption, lamp type, price and also user preferences collected through psychovisual experiments. However, these experiments induce subject fatigue, which limits the number of lighting alternatives that can be evaluated. To overcome this limitation, we propose a new protocol based on (1) the use of the internet and (2) an incomplete experimental design in which each subject judges only a subset of the whole set of visual stimuli. This protocol is validated by comparing three experiments conducted in the laboratory and online. No statistical difference was highlighted between the results of the experiments. Extrapolations suggest that this protocol could be used to assess up to 3000 visual stimuli.
In this paper, a natural lighting system composed of a tilted prismatic daylight collector, an outdoor reflector and an indoor diffuse reflector is described. The light emerging from the hypotenuse of the prismatic daylight collector is redirected onto the indoor reflector for natural light illumination. The results of measured illuminances are in agreement with the results of calculation. The prismatic daylight collector not only decreases discomfort glare but also collects daylight for the natural lighting system. The open natural lighting system, which uses less material, can be realized by the detailed analysis of the characteristics of the light emerging from the hypotenuse of the prismatic daylight collector for sunlight incident on the collector.
A novel design of phosphor-converted, white light emitting diode-based bicycle head lamp producing sufficient illuminance on the target to meet the K-mark regulations and additional illumination on the ground is proposed and demonstrated. The phosphor-converted, white light emitting diode has a power demand of 2.5 W, while the novel design offers a maximum illuminance of 30 lux at the HV point, and illuminances larger than 3 lux across the first 7 m on the ground. The optical utilisation factor for the target illumination is 30% and for the ground is 44%. It means that around 74% of the luminous flux emitted by the phosphor-converted, white, light emitting diodes is utilised. This novel and highly efficient bicycle head lamp provides safer illumination for bicycle riders.
Sleep disorders are problematic for persons with dementia and their family caregivers. This randomized controlled trial with crossover evaluated the effects of an innovative blue-white light therapy on 17 pairs of home-dwelling persons with dementia and their caregivers. Subjects with dementia received blue-white light and control (‘red-yellow’ light) for six weeks separated by a four-week washout. Neither actigraphic nor most self-reported sleep measures significantly differed for subjects with dementia. For caregivers, both sleep and role strain improved. No evidence of retinal light toxicity was observed. Six weeks of modest doses of blue-white light appear to improve sleep in caregivers but not in persons with dementia. Greater or prolonged circadian stimulation may be needed to determine if light is an effective treatment for persons with dementia.
In recent years, green energy has been the subject of many studies and has attracted great attention throughout the world. Many studies have focused on illumination with sunlight as a means of saving energy and creating healthy lighting. In this research, we present a novel circle-focus Fresnel type concentrator. Each part of the reflector corresponds to different angles of incident rays, the purpose being to increase the tolerance of the concentrator. This strategy is different from the conventional approach but is easy to implement.
Optimum use of natural light in buildings requires knowledge of the luminance distribution of the sky. Since the introduction of the CIE Standard General Skies, several methods have been proposed to find the frequency distribution of sky types. This paper presents a method whereby the ratio of the luminances of two sky elements and the ratio of the luminance of one sky element to the horizontal illuminance can be used in the determination of sky type.
The use of LEDs is increasing rapidly in both the commercial and residential markets. Nowadays, the main way to measure the luminous intensity distribution of a LED is by using a goniophotometer. This takes a long time which means its test efficiency is low. In this paper, we will propose a new way to measure the luminous intensity distribution of LEDs based on the Luneburg lens, which is a kind of dielectric lens with continuously changed index of refraction, with high efficiency and low cost. We also develop a complete test system and give the result of a simulation of the test system.
Two mock-up office rooms, one with a spectrally tuneable LED lighting system and the other with a fluorescent lamp (FL) lighting system were built for user acceptance studies for office lighting. One room was illuminated with six LED luminaires and the other with six FL luminaires. Each LED luminaire has 480 LEDs (20 different LED types and 24 of each type). Each FL luminaire has eight fluorescent lamps, four with a correlated colour temperature of 4000 K and four of 6500 K. User acceptance studies in the office environments were conducted with 40 observers, each observer having 16 sessions (six LED spectral power distributions (SPDs) + two FL SPDs and two illuminances (500 lux and 300 lux)). The observers performed office-related tasks while being totally immersed in one of these lighting conditions. The objective of this study was to verify previous results obtained in small-scale booth experiments and to further study peoples’ preferences for LED office lighting. The small-scale experiments showed that LEDs with a higher value of reference-based colour metrics (such as colour quality scale (CQS) colour preference scale) and with a higher value of area-based or volume-based metrics (such as CQS gamut area scale or gamut area index) were preferred by the observers. The office room study of the present work validated the findings of the earlier experiments but now in an office lighting environment. Furthermore, the observers preferred 4000 K to 6500 K at a light level of 500 lux and the light level of 500 lux over 300 lux. It was also found that the simplest LED SPD with three peaks has similar colour quality characteristics to complex LED SPDs with several peaks.
The European Union has financed a 3-year research project to establish optimal spectral power distributions of LED light sources for use in offices, commerce and homes. This paper summarizes the general questions relevant to colour preference investigations and introduces the investigations performed in the three laboratories that participated in the research. Subsequent papers will deal with details of the investigations and provide recommendations for optimum spectra in different indoor applications.
In order to determine user acceptance for light-emitting diode (LED) office lighting, a full-scale experiment was conducted in two mock-up office rooms with different light spectra at two different illuminances. Six LED spectra and two fluorescent lamp spectra were used for the study. There were four spectra (three LED spectra and one fluorescent lamp spectrum) at a correlated colour temperature (CCT) of 4000 K and four spectra (three LED spectra and one fluorescent lamp spectrum) at a CCT of 6500 K. Forty observers evaluated the lighting environments under different spectra and rated the lighting environments sitting at a working desk and at a meeting table. The observers preferred the task illuminance of 500 lux to 300 lux and the CCT of 4000 K to 6500 K. The observers preferred the spectral power distributions (SPDs) under which they found the lighting environment to look brighter and more spacious. The observers’ preferences showed that spatial brightness was affected by illuminances and SPDs. The lighting with a SPD having higher values of a reference-based metric (CQS Colour Preference Scale) and an area-based metric (CQS Gamut Area Scale or Gamut Area Index) was preferred most at a CCT of 4000 K. It was also found that the lighting with the fluorescent lamp was least preferred among the other SPDs at the CCT of 4000 K. The observers preferred both the simple and complex SPDs over fluorescent lamps at 4000 K in the office environment. It would be a good option to develop simple LED SPDs while maintaining the criteria of good lighting for an office environment.
In previous user-acceptance studies conducted at Aalto University, it was found that the preferred light-emitting diode spectral power distributions (SPDs) were not characterised by a high-CIE colour-rendering index but by a high-colour quality index (CQS) colour preference scale (Qp) and a high-CQS gamut area scale (Qg). In these studies, the SPDs were realised with a 12-channel LED spectra simulator. It is, however, foreseen that LED light sources consisting of 12 different types of LEDs will not be commercially exploitable due to complexity. The objective of this work was to investigate the possibility of generating simplified LED SPDs having CQS Qp and CQS Qg values similar to those of the preferred complex LED SPDs found in the previous user-acceptance studies. User-acceptance studies were carried out in lighting booths to investigate people’s preferences for the lit environment under both the complex and simplified LED spectra. The results suggest that the preferred complex LED SPDs can be optimized both for efficiency and cost without sacrificing the colour quality of the light.
High-power integrated LEDs usually have a bright square surface. When the rays emitted from them are collected to project a round spot at a very short distance using a rotationally symmetrical reflector, there will be a dark spot in the centre. This problem can be avoided in advanced lighting systems. A discontinuous surface reflector is designed by a simple method based on the three-dimensional form of compound parabolic concentrators. The dark spot is removed, and the uniformity is better.
We propose an innovative vehicle headlight design based on a highly efficient LED light pipe system. In the system, light rays are emitted from multiple high-power LEDs in front of a total internal reflection (TIR) lens. After passing through the TIR lens, the rays are divided into two beams by a prism splitter, and each beam is guided to each headlamp by a light pipe. We propose the system because it uses fewer LEDs but provides enough lumens and reduces the number of TIR lenses required. Detailed analysis of the system is given, and the simulation results show that the headlamp produces a legal Economic Commission for Europe (ECE) low-beam pattern, with a total optical efficiency up to 40.2%, when four LED (Lumileds-K2) sources are used.
This paper introduces luminance gradient as a metric for evaluating common non-uniform luminous environments. Luminance gradient is defined as the largest change rate and the polarity of spatial luminance variation on a large surface or across the entire field of view in high resolution. The metric, a visualization method, and a freely available MatLab code for plotting luminance gradient maps have been developed. The retinal resolution of pixels for mapping luminance gradient has also been identified. A camera-aided measurement method of luminance gradient is proposed, which is demonstrated in two case studies of the evaluation of different types of luminous environments. Moreover, this study explored whether luminance gradient could also be obtained from computer simulations using lighting software programs AGI32 and HeliosPro.
In this paper, an energy efficient streetlight for pedestrian roads is introduced. Energy efficiency is achieved via up-to-date light-emitting diode (LED) technology and added intelligence utilising integrated sensors and wireless control. Thermal and electrical design of the luminaire contributed to good technical functionality. The performance of the luminaire was validated with testing. The luminaire was compared with commercial lamp and LED-based street lighting technology by technical values and user acceptance. Energy savings of 19–44% through improved luminous efficacy was demonstrated without added intelligence. With smart control further power saving potential of 40–60% was shown depending on the lighting environment and pedestrian presence. User feedback of a pilot installation comparing commercial luminaires with the newly developed streetlight revealed that on average the users preferred the developed streetlight over the commercial luminaires.
Daylight has been associated with multiple health advantages. Some of these claims are associations, hypotheses or beliefs. This review presents an overview of a scientific literature search on the proven effects of daylight exposure on human health. Studies were identified with a search strategy across two main databases. Additionally, a search was performed based on specific health effects. The results are diverse and either physiological or psychological. A rather limited statistically significant and well-documented scientific proof for the association between daylight and its potential health consequences was found. However, the search based on specific health terms made it possible to create a first subdivision of associations with daylight, leading to the first practical implementations for building design.
A psychophysical experiment has been carried out to investigate the impact of dynamic lighting parameters on atmosphere perception. The experiment was conducted in a purpose-built LED lighting lab, where the lighting could be spatially and dynamically changed and colorimetric specifications controlled. The aim of this study was to investigate the impacts of speed, saturation and brightness of dynamic lighting on the perceived atmosphere, preference and suitability for certain spaces. Twenty native Chinese observers participated in the experiment, each assessing the environment under dynamic lighting conditions using 21 atmosphere terms. The results show significant gender differences on some scales such as safe, spatial, chilly, formal, preference and office-like. Factor analysis showed that the 21 scales can be grouped into three categories: tenseness, coziness and liveliness, and that a living room-like atmosphere evaluation is consistent with coziness. Dynamic lighting does have a significant influence on atmosphere perception. A more saturated LED light would lead to less tense, more cosy, more safe and more lively atmosphere perceptions. By increasing the speed, a more tense and less cosy atmosphere can be generated. Medium speed offers the most lively and preferred atmosphere. Brighter lighting will generate a less tense environment. More saturated colour and a slower speed will produce a more living room-like environment, but it seems that such dynamic lighting is not suitable for an office-like environment.
The aim of this paper is to present the colorimetric and photometric results for a pulsed power supply operated high pressure sodium (HPS) lamp. Especially, we are interested in controlling the spectral response radiation of the yellow D line. This sodium D line is composed of two spectral components, one at 589.6 nm and the other at 589.0 nm. The pulsed power supply is a driver for the HPS lamp based on the application of a low frequency (50 Hz) square current waveform through the lamp with one or more pulses on each half cycle. A description is given of the physical modeling of the arc’s behaviour. Experimental results obtained from our laboratory power supply for a 400 W HPS lamp supplied at 50 Hz and simulations are shown.
Different sizes and arrangements of solar bottle bulbs might greatly affect the lighting delivered and there is no general agreement on the best interior bottle exposure levels. This study was undertaken to examine the lighting performance of three prototype solar bottle bulbs and to compare their performance at three different interior bottle exposure levels: one-third, half and two-thirds. A solar bottle bulb made of one 1.5 litre bottle proved to be better than a solar bottle bulb made of three 0.5 litre bottles. In terms of interior bottle exposure levels, the half level performed the best. Some inexplicable phenomena were also observed with recommendations for further study.
Face recognition is one of the interpersonal judgements carried out by pedestrians. Road lighting should enhance the visual component of such judgements after dark. This paper presents experiments carried out using two different procedures, identification and perceived recognition, to investigate why earlier studies have led to inconsistent conclusions about the influence of spectral power distribution (SPD) on face recognition. For the identification procedure, two observation durations were employed (1 s and 3 s). The two procedures led to similar conclusions regarding recognition ability at different distances. Review of these and past results suggests that an effect of lamp (SPD) is more likely to be found when the task is difficult, i.e. small size, brief observation and correctly naming the target rather than simply picking a face from a sample.
In order to implement the recommended Commission Internationale de l'Eclairage (CIE) system for mesopic photometry to roads, it is necessary to define the relevant visual field and adaptation luminance in night-time driving conditions. We measured three drivers’ eye tracking on a rural road at night and in daytime, and the simultaneous luminance for the corresponding parts of the scene on lit and unlit sections of the road at night. Fields of view with circular sizes of 1°, 5°, 10°, 15° and 20°, with the centre point at the mode of the gaze distributions of the drivers, were used as initial estimates of the visual adaptation field. In both the lit and unlit sections, the variation within subject and between subjects in the mean luminance decreased as the size of the circular field increased. However, the mean luminances of all of the circular fields in the unlit section were higher than in the lit section due to the use of high-beam headlights in the unlit section.
In this paper, a high-frequency dimmable electronic power supply for the high-pressure sodium lamp is presented. The method includes a full bridge rectifier generating a dc-link voltage and a half bridge inverter to generate a frequency swept lamp power signal to drive the lamp while avoiding acoustic resonance. A dimming technique for a resonant circuit electronic ballast based on a variable frequency is introduced. In addition, the ability in the dimming range is demonstrated by experiments and simulation in order to verify the performance of the proposed circuit. A dimming range from 100% to 50% has been achieved. The efficiency is always higher than 89% and the ballast can accurately follow a fixed dimming plan.
There are currently no accepted metrics for summarising lighting conditions in studies aimed at investigating effects mediated by the circadian system. The objectives of this paper are to propose a set of metrics for capturing circadian variations in environmental lighting conditions and to compare two different lighting regimes applied to patient rooms. Our metric design emphasises the characterisation of light stimuli over time, e.g. their spread over one or more days. Lighting measurements for comparative assessment were taken in 20 beds in the intensive care unit of the Jeroen Bosch Hospital. Lighting conditions between the intensive care unit beds differed significantly across a number of circadian metrics. The proposed set of metrics offers a simple yet comprehensive approach to characterising lighting conditions from the circadian perspective with direct application in clinical studies investigating the effects of light on health.
The objective of this work is to propose to the urban physics community an optimal sky vault partition able to support most existing applications, either in daylight availability evaluation or in shortwave energy budget estimation. This partition is explained and justified. Its refinement is examined and analysed with respect to the studies performed today at urban level. The solution of the analyses is obtained in two steps: the heaviest part is the solution of the urban interreflection problem, while the second step is very fast and can be achieved in interactive mode. It consists in computing the thermal or illumination loads which will be used as coefficients of a recombination of the first step results. The urban interreflection problem is independent of this process and can be obtained with various existing techniques, such as the radiosity method.
CIE 191:2010 recommends a mesopic photometry system that defines the luminous efficiency function for peripheral visual tasks, which vary depending on the adaptation state of observers. For implementation of the system, an adaptation field to determine the adaptation state needs to be defined. To address this issue, vision experiments have been conducted to measure surrounding luminance effects on the adaptation state at a peripheral task point. The results reveal that the adaptation state depends mainly on the local luminance at the task point but there is also a small effect of the surrounding luminance. The results suggest that the surrounding luminance effect is larger than the veiling luminance predicted with existing foveal models; nevertheless, it is not significant for the mesopic luminance on uniform luminance distributions.
Smart lighting is used to provide the right light to meet occupants’ needs for efficiency, productivity and health. The development of adaptive control in smart lighting requires advanced real-time sensing technologies for monitoring the generated light field. This paper introduces a systematic approach to dynamic light field sampling using a distributed sensor network. A dynamic adaptive sampling algorithm is introduced to guide the adaptive selection and real-time reallocation of sample locations to track and estimate the generated light field and the daylight field. This approach generates a multi-scale functional representation of the light field, which can be an effective basis for lighting control. Experimental results have shown that a systematic dynamic selection of sensor locations can significantly reduce the error in representation of the light field with corresponding improvement in the lighting control.
By measuring illuminance values on the six facets of a small cube, a range of spatial illumination metrics can be determined. Some researchers have reported practical difficulties in doing this, and so this research note proposes a novel procedure for measuring cubic illumination that avoids the reported difficulties
This paper presents a joint blind and light control scheme for lighting energy optimization in a lighting control system. The proposed scheme utilizes the maximum available daylight without any glare and reduces lighting energy consumption while satisfying the user’s light level requirements. The optimal blind tilt angle that transmits the maximum available daylight without any glare is computed based on the sun’s altitude and the window’s orientation, and an optimization problem is formulated that minimizes the required artificial lighting energy to satisfy the user’s lighting requirements. The simulation results show that, relative to conventional lighting control schemes, the proposed scheme achieves improvements in lighting energy consumption while satisfying the anti-glare and user’s light level requirements.
The study presented in this paper aims to evaluate if and how the environment affects the circadian impact of a light source by predicting circadian stimulus (CS) resulting from the exposure to different light scenes, using equations reported in studies by Rea et al. The main findings are: (1) Above 600 lx at eye level the increase of CS is little; (2) Between 50 lx and 200 lx at the eye level an increase of only 50 lx determines a significant increase of CS; (3) Light sources with correlated colour temperatures between 2900 K and 4200 K have similar impacts on the circadian system according to the calculation method used; (4) Even an almost neutral environment affects the circadian impact of a light source.
The increase in the LED junction temperature is an important problem since it directly affects the lumen output and the colour characteristics of the LED chips, resulting in low performance in LED-based lighting systems. In this study, commercial computational fluid dynamics software is used with the JEDEC’s two-resistor compact thermal model to analyse the temperature distribution in two selected luminaires. It is aimed to show that use of the two-resistor model and measurement combination is a fast and easy way of predicting thermal behaviour of the system and LED junction temperatures instead of trial and error designs and thus ensures a better estimation for the total luminous flux of the luminaire and lowers the costs and time required for the prototyping processes.
This paper describes the application of Kriging techniques to the interpolation of light field models that include both three-dimensional spatial variation as well as angular directional information. In general illumination applications, this representation of the light field raises the challenges of high-dimensionality and anisotropic estimation. Discrete sampling of the light field based on simulation or physical measurements is not sufficient to support analysis and design studies. In this paper, Kriging techniques, which are widely used in spatial estimation, are introduced to address these problems. The principle of universal Kriging with dynamic trend is presented and incorporates the method of correction for negative Kriging weights. The results of this approach are described for a five-dimensional light field based on examples using both ray-tracing simulation as well as physical measurements in an experimental room with colour-controlled LED illumination sources. Using the weight-corrected universal Kriging technique, the overall light field in space is estimated and details may be explored by interpolation at specified positions and viewing angles. The proposed method provides a consistent and computationally convenient approach to analysis and design of the five-dimensional light field in space.
This study proposes a supplementary lighting and regulatory scheme for application in semi-closed crop production systems. This supplementary lighting control module is primarily based on fuzzy logic inference and an expert database. Under the hypothesis that the temperature and humidity conditions are consistent, the system will implement supplementary lighting of different wavelengths according to current solar spectral distribution conditions and plant growth patterns. Simulations demonstrate that under the condition of full sunlight, the system still provides supplementary light to compensate for insufficient light spectrum. Compared to traditional plant lamps that need to be lit for long periods of time, this system can randomly adjust light spectrum and intensity to achieve energy savings, and is therefore suitable for application in lighting control systems in future greenhouses.
Two studies were designed to investigate the carryover effects of daylight on performance and self-reports of sleepiness. The effects of daylight and of darkness were compared independent of the effects of simultaneous periodic, 1-hour exposures to narrow-band blue and red lights over the course of 26-hour sessions. Nighttime performance on a 54-minute tracking task, but not subjective sleepiness, was significantly better following exposure to daylight. There was no differential effect on performance or sleepiness from exposure to the blue or red lights. Eight of the participants returned to experience a completely dark session and a replication of the daylight and intermittent blue light session. Nighttime performance and subjective sleepiness were significantly worse for the dark session than for daylight-plus-blue sessions in both studies.
To synthesise a spectrum with a given radiant flux by multi-channel light-emitting diodes, different light-emitting diodes should have different radiant fluxes to maximise the light-emitting diode flux utilisation rate defined by the radiant flux of the light-emitting diode’s contribution to the synthesised spectrum divided by the rated radiant flux of this light-emitting diode. The optimal rating radiant flux algorithm for each light-emitting diode is achieved by applying the norm-reducing process and full-search method to the norm region of the spectra. As a result, light-emitting diodes with a broader full-width half maximum, such as phosphor-converted light-emitting diodes, are usually set at a high power level and the rest of the light-emitting diodes can be set to either medium or low power levels. Furthermore, the high-power light-emitting diode can be decomposed to some low-power light-emitting diodes to reduce both heat generated and light-emitting diode price.
Although manufacturers recommend light-emitting diode technology for all types of urban lighting, it is likely that high-pressure sodium lamps will be used for roadway lighting for many years. The purpose of this paper is to establish whether electronic ballasts represent a better solution for such lamps than electromagnetic ballasts. Special attention was devoted to the fact that electronic ballasts allow considerably higher voltage drops. However, taking into account the earth-fault protection demands, it is shown that electronic ballasts provide only a modest possibility to increase the length of the street lighting section. The techo-economic analysis showed that, owing to the high prices and shorter life of electronic ballasts, conventional electromagnetic control gear still represents a better choice from the financial point of view.
During the first stages of building design, issues such as local climate, surrounding buildings and orientation are determining factors. The impact of these boundary conditions on daylight illuminances in an open-plan office space is studied in terms of daylight factor, daylight autonomy and useful daylight illuminances. Climate conditions in the location determine the characteristics of the daylight source, such as the ratio between diffuse lighting and global lighting. However, surrounding buildings and elements which may block daylight in the space hold more weight than the orientation of glazed façades, but are not always taken into consideration in daylighting studies.
This study is based on a general interior lighting installation and discusses the relation between veiling luminance and the unified glare rating. Through curve fitting and a derived formula, a transfer function between veiling luminance and the unified glare rating is generated. This result connects disability glare and discomfort glare within a finite range, where the relation between them is almost linearly dependent. This transfer function has a high accuracy as shown by a comparison between the calculated results and the original data, and is the first to provide a connection between disability glare and discomfort glare.
Ceramic metal halide lamps with rated powers of 70 W and 150 W are dimmed by reducing their operating power. Under dimmed conditions, photometric, colorimetric and electric parameters, as well as the temperature distribution of the outer wall of the arc tube have been measured. As the lamp power is reduced, luminous efficacy and colour rendering index decrease while correlated colour temperature rises. For each lamp, at 70% of its rated power, the luminous efficacy is greater than 80 lm/W, colour rendering index is above 74 and correlated colour temperature increases by less than 800 K. Dimming applications of these lamps are validated by these parameters. Furthermore, the complicated variation of lamp parameters as a function of operating power is explained by the variation of metal halide vapour pressure with wall temperature.
A large number of physical dimensions and different criteria make choosing the optimal luminance distribution for outdoor lighting difficult. The optimisation becomes even more complex for light-emitting diode-based lighting installations that can be intelligently operated, providing different luminance distributions around a moving traffic participant. This study aims at establishing the main subjective factors for the assessment of the luminance distribution of an intelligent light-emitting diode-based outdoor lighting installation for pedestrians. Semantic-differential scales and Likert scales have been used to identify subjective impressions and to find the main factors for the optimisation of the control of the luminance distribution. Our results reveal two factors that need to be considered when assessing intelligent outdoor lighting installations: a major factor that is related to the subjective feeling of well-being and a minor factor that is related to the physical properties of the environment.
In order to extend the length of the coaxial cable connection between an electrodeless fluorescent lamp and the associated electronic ballast, a new structure for electrodeless lamp systems is proposed in this paper. Impedance matching networks in the structure are analyzed and designed based on the transmission characteristics of coaxial cable. Efficient topologies and formulae for the matching networks are put forward. Experimental results for a 2.65 MHz electrodeless lamp system with up to 25 m of coaxial cable which validate the structure are presented.
This work discusses the relative significance of optical and neural mechanisms in letter contrast sensitivity under different conditions of environmental lighting. A study was carried out on 26 eyes with normal ocular health. Sixteen lighting conditions were obtained by combining different test luminances (from 10 cd/m2 to 600 cd/m2) and surround luminances (from 1 cd/m2 to 600 cd/m2). The results reveal a significant influence of optical factors (pupil size variations and glare effects) on contrast sensitivity when surround luminance changes, and a dominance of neural effects when test luminance changes. Furthermore, test size and illumination conditions are identified for which letter threshold contrasts are not sensitive to surround luminance changes.
The CIE colour rendering index (CRI) has been criticized for its poor correlation with the visual colour rendering of many spiked or narrowband sources, its outdated colour space and chromatic adaptation transform and the use of a small number of non-optimal reflectance samples that have enabled lamp manufacturers to tune the spectrum of a light source to yield, in some cases, inappropriately high general CRI values. The CRI2012 metric proposed in this paper addresses these criticisms by combining the most state of the art colorimetric colour difference model, i.e. CAM02-UCS, with a mathematical reflectance set that exhibits a highly uniform spectral sensitivity. A set of 210 real reflectance samples has also been selected to provide additional information on the expected colour shifts when changing illumination.
This paper describes a climate-based simulation framework devised to investigate the potential for the non-visual effects of daylight in buildings. It is part 2 of a study where the first paper focused on the formulation of the photobiological underpinnings of a threshold-based model configured for lighting simulation from the perspective of the human non-visual system (e.g. circadian response). This threshold-based model employs a static dose–response curve and instantaneous exposure of daylight at the eye to estimate the magnitude of the non-visual effect as a first step towards a simulation framework that would establish a link between light exposure at the eye in an architectural context and expected effects on the non-visual system. In addition to being highly sensitive to the timing and duration of light exposure, the non-visual system differs fundamentally from the visual system in its action spectrum. The photosensitivity of the retinal ganglion cells that communicate light exposure to the brain is known to be shifted to the blue with respect to the photopic sensitivity curve. Thus the spectral character of daylight also becomes a sensitive factor in the magnitude of the predicted non-visual effect. This is accounted for in the model by approximating ‘yellow’ sunlight, ‘grey’ skylight and ‘blue’ skylight to three distinct Commission Internationale de l'Eclairage (CIE) illuminant types, and then tracking their ‘circadian-lux’ weighted contributions in the summation of daylight received at the eye. A means to ‘condense’ non-visual effects into a synthesised graphical format for the year, split by periods of the day, is described in terms of how such a format could inform design decisions. The sensitivity of the simulation model’s predictions to prevailing climate and building orientation is demonstrated by comparing results from eight European locations.
In this paper, we propose a composite optical system for automotive headlamps. The system is composed of a paraboloid collimating reflector, an off-axis paraboloid reflector, a baffle and an imaging len. By using a LED as the light source, precise light distribution can be achieved. When making ray-tracing simulation for the composite optical system in TracePro, a clear cut-off line can be seen on the measuring screen, as well as a hotspot at the centre. The power consumption for the LED light sources in this system is less than 10 W, resulting in an energy efficiency of more than 58% and a maximum illumination of 26.76 lux at the centre hotspot.
A smart illumination system for greenhouses and growing rooms capable of controlling the quantity and quality of light emitted by a number of LEDs is described. The system uses lamps containing blue and red LEDs programmed to emit various spectra at sixteen different frequencies and ten different pulse widths. The performance of the system is evaluated by determining the effect of pulsed light emission at different frequencies with a pulse width of 50% on tomato plants (Lycopersicon esculentum). The results show that low frequencies (0.1, 1, 10 Hz) have higher quantum efficiency in photosystem II compared to higher frequencies (50 and 100 kHz) and continuous light. They also show that the electron transport rate decreases when the frequency of pulses increases.
Environmental impacts of light sources and control gears have been analysed in several life cycle assessments (LCAs). In contrast, this paper analyses the environmental impacts of an entire fluorescent lamp/luminaire combination. The environmental impacts of a fluorescent lamp luminaire with two T5 lamps and an electronic ballast are analysed in a variety of potential environmental impacts. The results show that the energy consumption during use dominates the total environmental impacts by 93% on the average, while manufacturing accounts for 7% and end-of-life less than 1%. The importance of energy consumption is dependent of the used energy source. Compared to a previous LCA of fluorescent lamp luminaire, the division of the results into life cycle stages is similar but there are differences in the numerical results.
In order to compare subjective impressions created by LED and metal halide ambient lighting, a pilot project was conducted in a Belgrade park. All general requirements for an adequate comparison of subjective impressions were fulfilled. The survey was conducted using a questionnaire related to all aspects the researchers considered relevant for subjective evaluation of illuminated pedestrian paths in parks. It was concluded that the respondents, both those who had and those who did not have previous knowledge in the field of lighting, strongly preferred the use of metal halide lamps for the illumination of parks, which is in opposition to the statements of some LED manufacturers. It was also shown that light level and feelings of safety and comfort are evaluated as most important.
In a dense urban environment, sky obstruction caused by high rise buildings causes minimal daylighting for interiors on lower floors and in deep interior spaces. Innovative daylighting systems can be used to enhance daylighting indoors using available sunlight. This paper presents an overview of recent developments of innovative daylighting systems. The daylighting systems, which are classified as light guiding, light transport, light diffracting, hybrid and integrated systems, have been reviewed and a comparison has been made with respect to ease of integration, durability, maintenance, availability, efficiency, light output and transportation. Suitability of climate has been identified with respect to each daylighting system. Recent research and development involves hybrid and integrated systems which have the advantage of providing lighting irrespective of external sky conditions. The advantages and disadvantages of each system are summarized. Compared to active systems, passive systems are environmentally friendly and their efficiencies are also higher. It is inferred that each system has its own unique principle of light transmittance and is suitable for certain climates. More research is required on developing daylighting systems which are environment friendly, less energy intensive, cost-effective and having ease of integration.
Coloured light is one aspect of modern aircraft cabin design. It could be used intentionally to influence thermal sensations: Coloured light may convey the impression that the environmental temperature is warmer or cooler than it actually is while still providing thermal comfort. A study was conducted in a light laboratory to test these assumptions. Subjects were exposed to different lighting situations, which were evaluated in terms of light and comfort. It was found that room temperature was perceived as being different depending on the colour of the lighting: In yellow light, room temperature was felt to be warmer than in blue light. Conversely, air quality was perceived as being higher and subjects felt more alert in blue light. All the coloured lighting situations tested were comfortable.
In order to evaluate the circadian effects of light, an approach based only on a circadian sensitivity function makes it possible to easily obtain efficiency functions and action factors. However, it does not take into account the circadian human response to light stimuli, which is not linear. Non-linear models are more sophisticated and accurate but they are not easy to apply. In this paper a proposal for an easy way to evaluate the potential ‘circadian effects’ of light sources is presented. Although the model is quite simple, results are in good agreement with those obtained by means of one of the most accurate non-linear models.
Daylight is limited in time and space. In situations where daylight is insufficiently available, virtual natural lighting solutions (VNLS), which are systems that artificially provide lighting and view comparable to those of real windows and skylights, can be promising. VNLS can turn currently unused floor space into space with daylight qualities. The space-gaining potential of VNLS in buildings can be predicted using computational building performance simulation. This paper describes the approach of modelling VNLS with a simplified view, using the Radiance tool to evaluate the lighting performance in a reference office. The VNLS are modelled as arrays of small light sources resembling the sky, the horizon and the ground. The simulation results show that VNLS with wide beam angles generally offer a better uniformity and a larger percentage of sufficiently lit workplane area compared to those obtained with real windows under overcast sky conditions, while the discomfort glare remains comparable to that received from real windows.
In this paper a system for obtaining the luminous intensity distribution of a small light source, based on high dynamic range imaging, is described. The system uses a dark room, a lambertian screen and a video-luminance-meter mounted on a workbench. The luminous intensity distribution of the light source is derived from the illuminance map on the screen by applying the photometric inverse law. The geometry of the system is presented and the measurements’ uncertainties are estimated. Finally, an application to a LED source is presented.
Permanent morning shift workers often suffer from impaired sleep and complain about increased fatigue during the day due to an early rising time in the morning. A controlled field investigation with female permanent morning shift workers was conducted, which evaluated the acute, monthly and seasonal psycho-physiological and productivity-related impacts of a dynamic ambient lighting scenario. Dynamic lighting had an acute psycho-physiological calming effect and positively influenced sleep latency and anxiety/depression ratings. Finally, productivity (decreased mean relative handling time) was increased during the winter. This field study contributes to the growing knowledge about biological lighting impacts during shift work. Furthermore it indicates lighting effects on productivity-related and subjective measures for a sleep-deprived working population.
A study was carried out in light booths to investigate user preference for different light spectra. Twenty-one LED spectra and three fluorescent lamps, all at three different correlated colour temperatures were used for the study. Sixty observers evaluated the lit scenes under different spectra for naturalness of selected objects, colourfulness of a Macbeth Colour Checker Chart, and the visual conditions of the lighting booths. The observers preferred the spectral power distributions (SPD) under which the chroma and colourfulness values of the object colours were higher. The CIE Colour Rendering Index was not a good indicator of the observers’ preference for the LED SPDs. It seemed that light sources with a higher CQS Gamut Area Scale and CQS Colour Preference Scale values were preferred by the observers as far as LED spectra were concerned. However, the CQS Gamut Area Scale calculated with a new version of the software (version 9.2) and the Gamut Area Index were suitable as indicators of observers’ preference for both the LEDs and the fluorescent lamp spectra. Because chroma and colourfulness values of object colours influence the observers’ preference, they should be considered as important factors for the selection of a colour preference index for light sources.
Attention restoration theory (ART) provides fruitful concepts for the investigation of the role of lighting in psychological and attention restoration. The present field study explores the idea that different outdoor lighting qualities may affect the perceived restorativeness of the night-time environment. It studies the relationships between the four components of ART (being away, fascination, extent and compatibility) and perceived lighting attributes (brightness, distribution, glare, colour quality, feeling of safety and pleasantness). Twenty-nine participants rated three walkway lighting environments and twenty-six participants rated two walkway lighting environments in suburban neighbourhoods. Subjective assessments suggested that lighting may have both positive and negative connections with the components of ART. The possible restorative potential of lighting deserves further research attention.
A novel method of reducing the energy consumption of street lighting using electronic ballasts was simulated on 277 units of 250 W high pressure sodium (HPS) street lights for a month. The design of the electronic ballast is detailed. A control system was utilised to dim the lights at hours of reduced traffic. The energy consumption was compared to that of the conventional system. The electronic ballast operates at a higher frequency and corrects any power distortion in the supply. Together with the light dimming capability, the electronic ballast increased the efficiency of the lighting system resulting in a monthly saving of 10.7 MWh, giving a monthly equivalent carbon dioxide reduction of 6.1 tonnes. In Malaysia, this would translate to a monthly cost saving of 37.7%.
To understand people's judgement of the naturalness of object colours and preference for the lit environment, lighting booth experiments were conducted. Seven different LED spectral power distributions, all at correlated colour temperatures of 2700 K, 4000 K and 6500 K, were simulated for high CIE colour rendering index (Ra), high colour quality scale (CQS) colour preference scale (Qp) keeping Ra = 80, high feeling of contrast index (FCI) keeping Ra = 80, high CQS relative gamut area scale (Qg) keeping Ra = 80, low FCI keeping Ra = 80, low Qp keeping Ra = 80, and for a mimic of a fluorescent lamp (FL) in terms of the closest possible value of the Ra, FCI and Qp to the reference FL. Other metrics such as the gamut area index (GAI), memory CRI, and nCRI were also considered in the analysis. Sixty observers evaluated 24 lighting situations. This paper deals with a comparison evaluation, where LED lighting was compared to FL lighting. It was found that Ra does not explain the subjective naturalness of objects and the subjective preference of the lit environment for the different light sources. The results also indicate that people's judgement of naturalness and overall preference were explained better when a reference-based metric (such as Qp) and an area or volume-based metric (such as Qg or GAI) were both considered while maintaining the light source chromaticity difference (Duv) value within the limit ± 0.0054.
An algorithm is introduced to minimise the beam angle of compound parabolic concentrators (CPCs) with LED sources under the condition of a fixed exit aperture, as a big beam angle will cause large off-axis aberration and low efficiency for a projection system. According to the edge-ray principle and coordinates transform, the formula for the algorithm is derived with LED sources considered as extended sources. In this paper, an example is given to prove the algorithm. Not only the minimum beam angle but also the specific parameters of CPCs can be obtained by this algorithm.
Proper daylighting design in interior spaces reduces the energy costs of electric lighting and air conditioning. Daylighting directly affects human well-being and productivity. The benefits of daylighting have attracted increased attention, and architects and designers are now considering daylighting when designing new buildings. However, many existing buildings were not designed considering daylight, resulting in them being poorly lit and consuming considerable energy for lighting and cooling. Therefore, it is essential to explore the possibility of improving daylighting design in existing buildings by developing guidelines to transform them into energy-efficient and productive environments. This paper investigates the integration of laser cut panels in school buildings to improve their daylighting. The data are used to determine the best configuration when integrating laser cut panels into existing daylighting systems and to provide appropriate recommendations.
Multi-LED colour mixing light sources are increasingly being used in lighting. The method used to set the dimming signal needs to accurately achieve and sustain the desired colour temperature and high colour rendering index (CRI). A pulse width modulation (PWM) signal is always used in LED colour mixing. But the PWM switch state creates a time delay in the multi-LED current regulator, resulting in a colour difference. A modified PWM signal to accurately maintain the desired colour temperature and a high CRI is derived from a parameterised LED current regulator switch state, using curve fitting. The modified PWM signal can be calculated from reconstructed coefficients of the illuminant spectrum.
A large variability in response is usually found when assessing discomfort glare by semantic differential scaling. This issue may be addressed by considering the individual’s tolerance to glare, so we designed an experiment to describe the differences in glare sensation vote caused by a simulated window while glare-sensitive and glare-insensitive subjects performed a computer task. The luminance and size of the window had the same statistically significant effect on glare sensation for both groups. However, when occasionally looking directly at the glare source, glare-sensitive people experienced more glare than insensitive persons with a relative risk of being disturbed that varied from 2.70 to 6.75. Our data suggest that the glare threshold should be redefined to consider glare tolerance to achieve a glare-free, inclusive visual environment.
The use of light emitting diodes (LEDs) in outdoor lighting has energy-saving potential, but users’ responses to this light source are largely unknown. An intervention study in two residential areas compared conventional lighting installations (high pressure sodium in Area 1 and high pressure mercury in Area 2) to a retrofitted LED-alternative regarding residents’ perceptions of quality of light, visual accessibility and danger. Moreover, energy use was calculated. Residents’ (N = 60) visual accessibility improved and perceived danger remained low in both areas after retrofitting. In Area 2 the perceived quality of light increased, whereas in Area 1 the results were mixed. The retrofitted application reduced energy use by 41–76% and might be a feasible alternative to conventional outdoor lighting in relatively safe areas.
Electric lighting is one of the major energy loads in non-residential buildings. It is strategic to examine the real behaviour of available lighting control systems for practical applications so as to allow the development of strategies that can improve the reliability of measured data (in terms of illuminance at the desktop) and the consequent response of the control system. This paper presents a case study of an office where lighting data measured at the desktop and read by the automation system have been analysed. It also investigates the consequent response of the control system. In particular, we extrapolate data on the system's improvement margins and suggest suitable correction functions to be applied to the illumination data measured by ceiling-mounted sensors.
Recently, the CIE has adopted a range of 15 standard sky distributions covering the whole spectrum of usual skies found in nature. In a dense urban region, the external environment plays a significant role in daylighting designs. This paper studies an approach to calculating the average daylight factor for rooms facing heavily obstructed environments under overcast and non-overcast skies. The modelled vertical sky components under the various unobstructed and obstructed CIE Standard General Skies were determined. The performance of the proposed method was evaluated against the results obtained by computer simulations. The proposed approach provides a simple alternative for comparing daylighting designs for buildings facing different obstructed environments under various sky conditions.
This paper describes an investigation of the effect on electric lighting demand of applying occupancy models of various resolution to climate-based daylight modelling. The lighting demand was evaluated for a building zone with the occupant always present, with occupancy corresponding to absence factors, based on an estimated annual mean occupancy, based on estimated 1-hour mean occupancy, and based on 2-min occupancy intervals. The results showed little difference in the annual electric lighting demand when the same occupancy profile was used every day, as opposed to when profiles were used where occupancy varied every day. Furthermore, the results showed that annual electric lighting demand was evaluated slightly conservatively when a mean absence factor was applied as opposed to using dynamic occupancy profiles.
Energy-conscious facility designs strive to include natural daylight in workspaces. However, the correlated colour temperature (CCT) and spectral content of daylight varies throughout the day while existent electric lamps produce light with a fixed CCT, resulting in mixed-illumination environments. A prototype LED lamp, with a simple control concept and a novel pulse-width modulation drive circuit, is proposed. This white light over a broad range of CCT values while maintaining a stable colour quality fidelity score with respect to a standard daylight source having an equivalent CCT. This range of CCTs is obtained without requiring computations for spectral approximation, resulting in a simplified control system.
Important efforts are being made to increase electric energy savings in the field of lighting. Of all the different approaches possible, two are used more frequently than others: The use of lighting control systems and the replacement of old light sources with better ones. One direct effect of the employment of new light sources and light dimming controls is a decrease of the power quality of the electrical network. This paper addresses luminous and power quality measurements of different light sources that are suitable for office buildings. The measurements were performed with and without dimming. In this way, the luminous and the power quality characteristics of the light sources, at different light levels, were established.
This paper describes research on forward and backward light reflection of road surfaces for typical vehicle-related illumination and observation conditions. The aim is to improve luminance simulation in order to include quality criteria of headlamp light distributions that correspond to visual perception under night driving conditions. Measurements were performed under full scale conditions instead of the usual laboratory tests. Traffic safety requires tests under dry and wet conditions. The experimental data can be described by luminance coefficient-based models. Due to its fixed geometry, backward reflection can be covered with a single luminance coefficient. For forward reflection an angular dependent reflection model is described with which headlamp light distributions can be improved for their impact on automatically detected oncoming traffic even under wet conditions.
High-pressure sodium lamps are currently the main lamps used in public lighting. However, the possibility of using high-power light emitting diode (LEDs) for street lighting is growing continuously due to their greater energy efficiency, robustness, long life and light control. The aim of this paper is to study the power quality of high-power lighting networks based on LED and high-pressure sodium lamps. Both electromagnetic and dimmable electronic ballasts, which can dim the lamp output smoothly and uniformly, have been used connected to high-pressure sodium lamps. High-pressure sodium lamps connected to electronic equipment have been tested with different arc power levels using dimming on a 230 V power supply. The study presented in this paper is completely based on measurements, including harmonic currents in the frequency range up to 150 kHz for all the technologies. The main results show a broadband spectrum in LED lamps which confirms other research in fluorescent lamps powered by high-frequency ballasts. Results also indicate a decrease in the harmonic value with increasing harmonic order, and a decrease in the harmonic value at half load (60%) compared with full load (100%). Although total harmonic distortion of the current is lower with high-pressure sodium lamps connected to electronic rather than electromagnetic ballasts, LED lamps achieved the lowest total harmonic distortion of current.
An atrium creates indoor conditions mimicing outdoor space. One effective method for creating outdoor-like conditions is landscaping using various plants. This study aims to provide building designers with daylight availability data for plants in atria. With the Daysim program, which uses weather data for Incheon, Korea, the daylight autonomies (DAs) of four-sided open-top atria for 112 cases were determined according to the geometry and orientation. The main geometric indices adopted were the aspect ratio (AR) and the plan aspect ratio (PAR). The results show that the DAs for 750 lx and 1000 lx were negligibly affected by the atrium shape, while the DA for 2000 lx was notably affected by the AR. The impacts of the PAR and orientation on the DA for 2000 lx were prominent in atrium wells with ARs of 0.36.