Equating colors for saturation and brightness: the relationship to luminance

With a modified step-by-step brightness-matching procedure, a series of colors, with dominant wavelengths from 400 to 670 nm, was adjusted so that the saturations and brightnesses of the colors appeared equal to those of the reference, which was a mixture of 570-nm and white light. The results show that equally bright and equally saturated colors are not equal in luminance. We also report a saturation function of spectral lights derived by utilizing these equally bright and equally saturated colors. Finally, our equally saturated colors do not plot as a circle in the 1976 CIE u', v' space, which indicates some limitations of this uniform chromaticity diagram.