metamery

Metamery refers to the phenomenon in color science where two or more different spectral power distributions (SPDs) produce the same perceptual color under a given viewing condition. In other words, metamers are distinct light spectra or color stimuli that look identical to the human eye when viewed under a specific illuminant and by a given observer.

The underlying mechanism of metamery lies in the trichromatic nature of human color vision. The eye uses three types of cone receptors, each with its own spectral sensitivity. Different SPDs can stimulate these cones in the same way, leading to equal cone excitations and the same perceived color. Mathematically, two SPDs S1(λ) and S2(λ) are metamers if they yield the same tristimulus or cone response values for the chosen observer and illuminant. Because there are infinite SPDs that can satisfy this condition, metamers are a common and fundamental aspect of color matching.

Metamerism is highly dependent on lighting and observer characteristics. A pair of materials or colors may match under daylight but not under artificial illumination, a situation known as metameric failure. Changes in the observer, such as age-related shifts in cone sensitivity, can also alter metameric matches.

Applications and implications of metamery include color reproduction in printing, painting, and digital displays, where exact spectral matches are impossible but perceptual matches are pursued. Understanding metamery is essential for color calibration, quality control, and the design of lighting and display systems to ensure consistent color appearance across conditions. See also: metamerism, color matching functions, metameric failure.