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.