Toward a unified model for predicting color quality of light sources

Considering that the existing color quality (CQ) metrics for light sources cannot correlate well with the subjective evaluation, in an immersive environment equipped with a multichannel LED light source, a psychophysical experiment by categorical judgment method was carried out to assess the three perception-related CQ attributes of light sources in terms of naturalness, colorfulness, and preference. The experiment collected the subjective responses to these attributes of up to 41 metameric spectra at each of four test correlated color temperatures (CCTs) ranging from 2800 to 6500 K, which covers the usual white-light range for general lighting. The results indicate that preference exhibits relatively high correlation with naturalness and colorfulness, and naturalness is weakly related to colorfulness. Besides, 20 typical CQ metrics were adopted to examine their validity in characterizing the subjective data, confirming their limited performance. Meanwhile, the underlying relationship of these metrics and the subjective data was also analyzed by the multidimensional scaling, revealing that almost all metrics can correspond to one attribute of naturalness, colorfulness, and preference, and that the saturation level is identified as a critical factor affecting these attributes. Based on these results, a unified CQ model was developed with a multiple nonlinear regression equation combining the Illuminating Engineering Society of North America color rendition method. The model accords satisfactorily with the subjective evaluation, while being applicable to a wide range of CCTs.