quotient NC/ND of two collinear distances on the chromaticity diagram of the CIE 1931 or 1964 standard colorimetric systems, the first distance being that between the point C representing the colour stimulus considered and the point N representing the specified achromatic stimulus, the second distance being that between the point N and the point D on the spectrum locus at the dominant wavelength of the colour stimulus considered, leading to the following expressions:
Note 1 to entry: In the case of purple stimuli, the monochromatic stimulus is replaced by a stimulus whose chromaticity is represented by a point on the purple boundary.
Note 2 to entry: The formulae in
Note 3 to entry: The excitation purity,
Note 4 to entry: The excitation purity has unit one.
Note 5 to entry: This entry was numbered 845-03-48 in IEC 60050-845:1987.
Note 6 to entry: This entry was numbered 17-408 in CIE S 017:2011.