Color Perception & Metamers

Trichromacy & Metamers: Human color vision uses three cone types (S, M, L) whose sensitivities are captured by the CIE 1931 XYZ color matching functions. A color is uniquely determined by three numbers (X, Y, Z) — the integrals of the SPD against each CMF. Metamers are physically different spectra that produce identical (X,Y,Z) values: the eye cannot distinguish them. This is why a yellow LED and a mix of red+green LEDs can look identical. Illuminant metamerism means two fabric dyes that match under D65 daylight may appear mismatched under fluorescent F2 lighting — a real problem in the textile industry.