Color rendering: Beyond pride and prejudice

Abstract

It is a truth, universally ignored, that a single metric of color rendering must be in want of another. Evidence presented here, together with those from an earlier study, strongly suggest that the quest for a single metric to quantify color rendering will be in vain. Rather, the strengths of color rendering index (CRI) and of gamut area index (GAI) y seem to counteract the weaknesses of one another, such that together they can be used to guide lighting practitioners in choosing a source that will provide good color rendering of most objects in most applications. The present study was conducted to determine whether sources, both warm and cool, with high levels of both CRI (above 80) and GAI (above 80 and less than 100) were judged better than ones with high levels of just CRI or just GAI. The results support the conclusion that a two-metric system of color rendering is needed for general illumination applications.

A two-metric proposal to specify the color-rendering properties of light sources for retail lighting

“…Based on their work and initial recommendations by Figueiro et al, [31] Rea and Freyssinier recommended a lower (80) and an upper (100) limit to GAI. [5] [27] Perhaps more importantly, Rea and Freyssinier [27] tested the two-metric hypothesis and were able to show that when GAI is used to complement CRI, high values of both metrics (CRI ≥80 and 80≤GAI≤100) seem to ensure positive subjective impressions of naturalness and vividness, both considered important aspects of color rendering in retail applications. Additionally, sources meeting the CRI and GAI criteria seem to be generally preferred over sources with only high CRI or only high GAI when used to illuminate a multicolored display.…”

“…[5][27] Figure 2 shows graphically the target criteria for CRI and GAI of the sources listed in Table 1. [5] [27] …”

“…Recently, following the principles laid out by Bouma, [7] Judd, [9] and Thornton, [24] Rea and Freyssinier [26] [27] proposed a two-metric approach by complementing CRI with a measure of gamut area (gamut area index) as a practical approach to specify the color-rendering properties of light sources. The rationale behind the approach is that CRI and gamut area are indicative of fundamentally different, but relevant, aspects of color rendering.…”

A practical and predictive two-metric system for characterizing the color rendering properties of light sources used for architectural applications

“…They were able to demonstrate in an a priori test of this idea that, when used in conjunction with one another, sources with high CRI values and high (but not too high) values of GAI tend to be preferred over light sources that have high values of only one measure. 19 Thus, the two-metric approach to characterizing the color rendering characteristics of fabricated sources of illumination appears to successfully meet the expectations for daylight identified by Bouma 60 years ago. Table 1 lists, in addition to CRI values, GAI values for some commercially available light sources.…”

“…They also showed that GAI is predictive of color saturation, another important aspect of color rendering. 18,19 However, they discovered that objects' colors can be rendered poorly because the hues appear to be too saturated; thus, GAI can be too high for observer preference. Studies have indicated that people tend to prefer the slightly saturated colors for natural objects, but not when the saturation levels make the objects appear artificial.…”