Characterising user preference for white LED light sources with CIE colour rendering index combined with a relative gamut area index

The CIE general colour rendering index (R-a) 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 R-a values ranging between 70 and 100 and relative gamut area index (G(a)) 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 R-a 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 R-a in conjunction with G(a) and a colour rendering graphic for providing a more detailed description of the colour quality of white LED light sources.