Evaluation of changing the components involved in CIE color rendering index

Various improvement methods have been proposed to cope with the deficiencies of the Commission Internationale de l'Eclairage (CIE) color rendering index (CRI). However, standardizing these methods lack quantitative evidences. Accordingly, with numerous light sources having rich spectral properties, the changes in CRI scores before and after improvement were quantitatively evaluated in terms of six critical components, including reference illuminant, standard observer, chromatic adaptation transform, uniform color space, color difference combination, and the rescaling operation, involved in the CIE CRI calculation. The results indicate that the largest change in CRI scores occurs in improving uniform color space, especially with CAM02-UCS, and that the CRI scores of the sources with highly-structured spectra tend to be changed considerably by most improvement methods. Compared with the other CRIs, the change in the special CRI R9 is frequently much larger for almost all the improvement methods. The least change in CRI scores is caused by partly updating reference illuminants as the mixed illuminants of the Planckian radiation and CIE daylight, which should be the most acceptable improvement. Additionally, adopting a rescaling function with the original scaling factor could be a candidate for avoiding negative CRI scores without leading to significantly large change in positive scores. © 2020 Elsevier GmbH