Lightness
The perceived brightness of a colour on a scale from black to white, independent of its hue and chroma.
Formula / rule
L* = 0 (black) to 100 (white)
Measured in
L*
In depth
Lightness is perceptual rather than physical: an L* of 50 sits halfway between black and white to the eye, which corresponds to only about 18 per cent of the physical light — the same reasoning that puts middle grey at 18 per cent reflectance. Separating lightness from colour lets tone and hue be edited independently.
Examples in practice
Raising the lightness of the blue channel alone brightens a sky without changing how blue it appears.