metamers

Metamers are pairs or groups of color stimuli that have different spectral power distributions but appear the same color to the viewer under a given lighting. In color science, two materials are metamers if their reflected or transmitted light produce the same color sensation for a particular illuminant and observer, despite possessing different spectral reflectance or transmittance curves.

The phenomenon arises because human vision is trichromatic, relying on three types of cone photoreceptors. Many distinct spectra can evoke the same three cone responses, yielding identical tristimulus values under the chosen illuminant. The CIE 1931 color matching framework formalizes this mapping, so metamerism occurs whenever the spectra differ in ways that do not change the cone-driven color impression for the observer and light source.

Metamers have practical implications in manufacturing and quality control across textiles, paints, printing, and plastics. A color that matches under showroom lighting may look noticeably different under daylight or office lighting, leading to color quality issues. To mitigate this, color specifications are tied to standardized illuminants (such as D65 or A) and observers, and products may be tested under multiple illuminants to reveal metameric differences.

Metameric matches depend on both the illuminant and the observer. They can be described as simultaneous metamers (a match under one light that diverges under another) and are a central consideration in color matching, metrology, and perceptual color research.