Lightness

CIELAB is a colour space designed so that equal numerical steps look roughly like equal visual steps. Its L* axis is lightness. The other two axes, a* and b*, place the colour between green and red and between blue and yellow, and from them come chroma and hue angle.

Lightness is measured from the colour itself, so it is not the same as the brightness setting of a screen. Deep reds, wines and browns sit low on the scale; pale nudes and pastel pinks sit high. Two shades can share a hue and differ only in lightness, which is how a light pink and a deep rose can have the same hue angle.

The encyclopedia uses lightness to set each shade’s depth band and to judge contrast with skin. It is also one of the three parts of the ΔE colour difference: two shades that differ only in lightness look like lighter and deeper versions of the same colour.