lum function

The lum function calculates the luminance of a color and returns it. The luminance ranges from 0 to 1. To construct a color from hue, saturation, and luminance values, use the hsl or hsla functions.

Examples:

lum(rgb(1, 0, 0))        ; 0.5
lum(rgb(0.5, 0.4, 0.3))  ; 0.4
lum(hsl(1.5, 1, 0.5))    ; 0.5

See Also
red function
hue function
sat function
alpha function
Writing direct coloring algorithms