Subjective Assessment of Color Naturalness of Objects Illuminated by LED Light Sources with Various Color Rendering Index and Color Temperature

Abstract

Subjective evaluation of LED light sources is important because they have characteristic spectral distributions not similar to conventional light sources. Average color rendering index (Ra) is generally used as an index of color reproducibility of light sources. A simple question about “Ra” is that color temperature of light sources is not taken into account to the assessment methodology of color reproducibility. We suppose color temperature of light sources naturally affect to color reproducibility. In this study, we investigated quantitatively how Ra and color temperature of LED light sources affect color reproduction respectively. We prepared 8 commercial LED light sources which have various values of Ra and color temperature. Subjects observed 11 different objects, one by one, under each of the 8 different light sources, and assessed the color naturalness of each object under the 8 different light sources using 5 ranks of subjective score. We calculated correlation coefficients 1) between average color rendering index and subjective assessment, and 2) between color temperature of LED light sources and subjective assessment. Color temperature (correlation coefficients 0.58) showed clearly higher correlation to color naturalness than that of Ra (correlation coefficients −0.24). Thus, our subjective evaluation results have shown that color naturalness of objects is almost independent to average color rendering index of an illumination but evidently dependent to color temperature of the illumination.