What is Metamerism?
Also known as: metameric match, metameric failure
When two colours match under one light but not under another. A fabric that matches the standard in daylight can look different under store or home lighting.
Why can two fabrics match in daylight but not in a store?
Two samples are a metameric pair when they look identical under one light source but differ under another. It happens because the samples reflect light differently across the spectrum (for example, two dyes built from different colourants) and each light source contains a different mix of wavelengths. In textile colour approval, buyers therefore check a lab dip under several standard lights in a light booth, typically daylight (D65), a store fluorescent (CIE F11, the type commonly called TL84) and warm incandescent light (Illuminant A). A match that holds under all of them is robust; one that only holds in daylight is a metameric match and may be rejected. A screen preview cannot detect metamerism, because a monitor shows only one mix of light; spectral measurement or a physical light booth can.
What does metameric failure look like in production?
A navy lab dip matches the buyer's standard in D65 daylight, but under the store's fluorescent lighting it turns noticeably greener. The dye house reformulates with colourants closer to the standard's, and the new dip holds under daylight, store and warm light.