Metameric

Metameric is an adjective derived from metamerism, a term used in several scientific fields to describe a phenomenon where two or more entities share a property under one condition but differ under another. The most common contexts are color science, organic chemistry, and biology.

In color science, metamerism is the phenomenon whereby two colors with different spectral power distributions appear identical under one light source but differ under another. This occurs because human vision integrates light across wavelengths, while the illuminant’s spectral content and a material’s reflectance interact differently. Metamerism is a central concern in color matching for printing, textiles, and cosmetics; differences may only become apparent when viewed under daylight, tungsten, or fluorescent lighting. To control it, manufacturers use standardized illuminants and colorimetric measures, such as metamerism indices or tests under multiple light sources.

In organic chemistry, metamerism is a form of constitutional isomerism where two compounds have the same molecular formula and the same functional group, but different distribution of alkyl groups around that functional group. The resulting metameric pairs often show substantially different physical properties, such as boiling points and solubilities, even though they share the same functional group. The concept is commonly discussed in the context of carbonyl-containing compounds and other functional groups where substituent arrangement around the reactive center matters.

In biology, metameric describes a segmented body plan characterized by repetitive units, or metameres, as seen in annelids and many arthropods, and in certain developmental structures of chordates. Metamerism underlies patterns of growth, nervous system organization, and musculature in these groups.