colorimetric purity of a light

[4.6.6]

A quantity (p_c) defined by p_c = L₁/(L₁ + L₂), where L₁ is the luminance of a single-wavelength (monochromatic) light source, and L₂ is the luminance of the reference standard light source. These values are obtained by adjusting the reference standard light source until the additive mixture of the two match the color of the considered light source.

NOTE: This definition was changed in ANSI/IES RP-16-17 Addendum 4.