Spectral locus

The spectral locus is the outer, horseshoe-shaped curve of the CIE chromaticity diagram: every pure, single-wavelength color the human eye can perceive, from violet at one tip, sweeping through blue-green and green, round to red at the other. The straight line closing the bottom is the line of purples — the magentas, which have no single wavelength. Everything the eye can see sits inside this shape; nothing sits outside it. Because even the widest display gamut (Rec.2020) is a triangle that doesn’t fill the horseshoe, the spectral locus is the reminder that “wide gamut” is always relative to what the eye can actually perceive.

First used in: 3.1 · Color science foundations