colorimetric purity [pc]
quantity defined by the relation:
where Ld and Ln are the respective luminances of the monochromatic stimulus and of the specified achromatic stimulus that match the colour stimulus considered in an additive mixture
NOTE 1 In the case of purple stimuli, see NOTE 1 to "purity".
NOTE 2 In the CIE 1931 standard colorimetric system, colorimetric purity, pc, is related to excitation purity, pe, by the equation pc=pe yd/y where yd, and y are the y chromaticity coordinates respectively, of the monochromatic stimulus and the colour stimulus considered.
NOTE 3 In the CIE 1964 standard colorimetric system, a measure, pc,10, is defined by the relation given in NOTE 2, but using pe,10, yd,10 and y10 instead of pe, yd, and y respectively.