Metamerism (color)

Distinct spectra can give the same colour response for a specified observer and illumination. In a simplified three-cone cell model, equal values of $\int L(\lambda )R(\lambda )S_i(\lambda )d\lambda$ for $i=1,2,3$ need not imply identical spectral reflectance functions $R$. Altering illumination or observer can break the match.

A stimulus belonging to a pair of physically different optical spectra that match for a specified observer and viewing condition. Such a match exhibits metamerism. Changing the observer, adaptation or illumination can break the match.