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.