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Abstract
Correlated color temperature (CCT) is often used to represent chromaticity of white light sources, but chromaticity is two-dimensional, and another dimension, the distance from the Planckian locus, is often missing. Duv is defined in ANSI C78.377 for this purpose but is not yet widely used. In this article, the use of a combination of CCT and Duv is proposed as an intuitive expression of chromaticity of white light sources for general lighting. In addition, this article presents practical calculation methods to calculate CCT and Duv, having sufficient accuracy, within an error of 1 K, in a wide range of chromaticity, from 1000 to 20,000 K in CCT and −0.03 to 0.03 in Duv.
Notes
1 1. The (u′, 2/3v′) coordinate is equal to that in the CIE 1960 (u, v) diagram, which is now obsolete. CCT has historically been calculated using CIE 1960 (u, v). Changing to the 1976 (u′, v′) was investigated when CIE 15:2004 [CIE 2004] was published; however, the CIE committee then concluded to keep the CIE 1960 (u, v) as the basis for calculation of CCT.
2 2. The 1960 (u, v) coordinate, now obsolete, is used in this article for simplicity in expression and due to historical reasons for calculating CCT.