White is a color sensation absent hue. Manufacturers describe practical light sources used for illumination as tinted warm-white or cool-white, but these informal designations do not seem to be based upon measured human color perceptions of white illumination. This article describes the results of a series of psychophysical experiments that more precisely measured subjective perceptions of white illumination from light sources of different correlated color temperatures (CCTs). Generally, perceptions of untinted white illumination for sources with high CCTs (above 4000 K) are associated with chromaticities that fall above the blackbody locus. In contrast, perceptions of untinted white illumination for sources with low CCTs (below 4000 K) are associated with chromaticities that lie well below the blackbody locus.
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