Constant hue loci of unique and binary balanced hues at 10, 100, and 1000 Td.

Constant hue loci for unique red, yellow, green, and blue and the loci of four binary balanced hues (e.g., equally reddish and yellowish) were measured at 10, 100, and 1000 Td for two observers. Wavelengths of the unique hues were not invariant from 10 to 1000 Td. In Judd's modification of the 1931 CIE chromaticity diagram, only the unique yellow loci at 10 and 1000 Td plotted as straight lines. The other constant hue loci were curved, and all the constant hue loci changed with retinal illuminance.