Comparing Measures of Average Color Fidelity

ABSTRACT

The introduction of new measures of color rendition, especially IES TM-30-15, has stirred debate within the lighting industry on the relative merits of the tools, as well as the amount of difference between the new tools and prior tools, such as CIE R_a. This article focuses on comparing three measures of average color fidelity: IES R_f, CIE R_a, and CIE R_f. Using a large set of commercially available, experimental, and theoretical spectral power distributions (SPDs), the analysis contrasts past efforts to make similar comparisons using smaller or more focused data sets. It highlights the interactive effect of gamut shape and color space nonuniformity, which results in a range of IES R_f values of at least 50 to 86 for SPDs having a CIE R_a value of 80. It also examines how these differences can be overlooked in psychophysical experiments relying on a small number of SPDs, which can present misleading findings on the value and meaning of the measures. When considering the results, it is important to remember that average color fidelity is only one aspect of color rendition.

KEYWORDS:

• Color Rendition
• color fidelity
• IES TM-30-15
• Color Rendering Index (CRI)
• color preference

Funding

This work was supported by the Solid-State Lighting Program of the U.S. Department of Energy.

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

This work was supported by the Solid-State Lighting Program of the U.S. Department of Energy.