Improved Method for Evaluating and Specifying the Chromaticity of Light Sources

ABSTRACT

This article describes a method for calculating and specifying light source chromaticity using the International Commission on Illumination (CIE) 2015 10° color matching functions (CMFs), which, according to analysis of existing psychophysical experiment data, can reduce visual mismatch compared to specifications based on the traditional CIE 1931 2° CMFs in architectural lighting applications. Specifically, this work evaluates, documents, and recommends for adoption by lighting standards organizations a supporting system of measures to be used with the CIE 2015 10° CMFs: a new uniform chromaticity scale (UCS) diagram with coordinates (s, t), a measure of correlated color temperature (CCTst), and a measure of distance from the Planckian locus (Dst). It also presents options for updating nominal classification quadrangles. A complete method of this nature has not yet been standardized, which may be contributing to the slow uptake of the CIE 2015 CMFs. The proposed tools are analogous to u, v, CCT, Duv, and the American National Standards Institute (ANSI) C78.377 chromaticity specifications that are all currently defined in the CIE 1960 UCS diagram using the CIE 1931 2° CMFs. While conceptually equivalent, the differences between the current standard method and the proposed st system are important for reducing unintended visual mismatch in the chromaticity of light. The implications of changing chromaticity specification methods are identified by a comparison over a diverse set of real light source spectral power distributions.

KEYWORDS:

• Chromaticity
• CCT
• Duv
• CCTst
• Dst
• color matching functions

Disclosure statement

No potential conflict of interest was reported by the authors.

Author contributions

Conceptualization AD LW KS | Investigation LW MM MR KS | Methodology AD JL KH KS LW MM MR TE | Project Administration JL LW MR | Software LW MM MR KS | Investigation LW MM MR KS | Visualization MR KS | Writing – Original Draft MR | Writing – Review and Editing AD JL KH KS LW MM MR TE YO

Supplementary material

Supplemental data for this article can be accessed on the publisher’s website

Additional information

Funding

The work of Michael Royer was supported by the U.S. Department of Energy’s Lighting R&D Program, part of the Building Technologies Office within the Office of Energy Efficiency and Renewable Energy (EERE). No other authors received funding for the preparation of this manuscript.