Limitations of correlated colour temperature in visual perception and its implications for evaluating the colour rendition quality of indoor lighting

Abstract

Correlated Colour Temperature (CCT) is a crucial parameter for white light sources and it is closely related to the colour rendition quality of indoor lighting. In this study, two psychophysical experiments were conducted to examine the CCT recognition error of human observers and then investigate the relevant influence on the qualification of colour rendition quality. In Experiment 1, 36 lighting designers were invited to participate in a CCT recognition test with CCT values ranging from 3000 K to 6000 K, by which we obtained their recognition errors and discriminable intervals. It was found that even lighting professionals cannot recognize the CCT value very accurately and that CCT did not correlate linearly with visual perception. In Experiment 2, we further explored the influence of lighting designers’ CCT recognition errors on colour preference and discrimination judgements toward 8 kinds of objects with 50 naïve subjects by constructing a typical indoor lighting scenario. It was found that due to the CCT recognition errors revealed in Experiment 1, even professional lighting designers could hardly select the most appropriate CCT for a specific lighting scenario in terms of colour preference and colour discrimination. We hope those findings could provide a deeper understanding for the concepts of CCT and colour rendition of indoor lighting. As we believe, for quantifying the visual attributes like colour preference and discrimination, an absolute and global metric whose calculation protocol is independent of CCT value should be advocated.