A colorimeter was constructed to measure the size of just-noticeable color differences as a function of observer adaptation. It was of the Burnham type with 1.6° test and matching fields and a 15° adaptation field that had a luminance of 3400 cd/m2. Nine different adaptations were used: dark adaptation, adaptation to five near-planckian white-light sources that had color temperatures in the range 6500–2000 K, and adaptation to three colors, red, green, and blue. Very little difference was found between the sets of discrimination data obtained for adaptations to the five white lights; a slight increase of the size of the just-noticeable color difference with decreasing color temperature was observed. To permit the data to be compared on a basis of equal appearance, rather than equal chromaticity, the colorimeter was modified so that color-appearance shifts could be measured, using a binocular-matching technique. Appearance-shift matrices were computed from the experimental results so that the discrimination data for each adaptation could be plotted in terms of the appearance of colors with adaptation to 6500 K. The results for the white-light adaptations showed that there was very little difference between the data when plotted directly and the data plotted as they would appear in 6500-K adaptation. This was also found for the results obtained with dark adaptation, but it was not true for the results obtained for color adaptations.
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