Excitation purity

The excitation purity of any color possessing a dominant wavelength is an exactly defined ratio of the distances in the chromaticity diagram indicating how far the given color is displaced towards the spectrum color from the achromatic color.

The excitation purity of EP is determined by the following distance ratio:

where

xP, xW and xld are the chromaticity coordinates at the color P, the white point W and the dominant color ld respectively,

and the white point is given by xW = yW = zW = 1/3

For a color without a dominant wavelength as Q, the excitation purity EPc is determined from the complementary wavelength.

where EP is calculated using the complementary wavelength lc.