Luminance–brightness comparisons of separated circular stimuli

An experiment was conducted in which observers adjusted the luminance of a 2856-K white comparison source to appear as bright as a chromatic source of known luminance. Twenty different chromatic sources were used, each subtending a visual angle of 1 degree. The results show that, for sources having the same dominant wavelength, the amount of white light required to make a brightness match increases as saturation increases. Additional observations were made using four of the chromatic sources at viewing subtenses of 20' and 6'. These results show that the amount of white light required to make a brightness match decreased as the source size decreased. The rate of decrease was most rapid for the red source.