Metamerism, why does the color change?

For there to be color there must be light. The objects absorb or reflect certain wavelengths, and it is the reflected ones that give them their color, but why does it sometimes look different when looking at an object under artificial light when we look at it in sunlight? What makes light cause drastic changes in the colors we perceive?

In general, the perception of the color of an object depends not only on the object itself, but also on the source of illumination, the area surrounding the object and the human brain. These parameters when altered can affect the perceived color. One of the cases in which this happens is known as metamerism.

Metamerism or metamerism is a phenomenon where two color samples that appear to be the same under a light source, are not under another one, due to the spectral reflectance (color reflection) of a material or color sample.

There are four types of metamerism:

Illuminance: It occurs when the color of two objects coincides under a light source of a particular observer, but looks like a different color under another type of lighting.

Observer: Under the same conditions of angle, distance and lighting, color samples can be perceived identical for one observer while for another they become disparate, it is considered the most subjective.

Geometric: Two equal color samples can be perceived as different if the object's angle of view changes, this is due to the reflectance of certain materials.

Distance or field: The difference occurs when the distance of the observer varies and the position of the object observed even if the same lighting conditions are maintained.

This phenomenon, beyond affecting daily perception, has forced different industries such as textiles, automotive, printing, painting and others to look for methods, instruments and systems such as glossometers, colorimeters, visual evaluation booths or spectrophotometers to improve their control of quality and thus minimize the effect of metamerism when designing and producing your items.

In the case of visual evaluation booths, their function is to simulate real scenarios of artificial, incandescent or fluorescent lighting (with standardized measures) to evaluate color samples. If the color changes in the object are minimal under the three lights main tests can be considered acceptable samples.

On the other hand, spectrophotometer tests evaluate the properties of the samples in two or more illuminants (duly standardized light sources) such as daylight or incandescent light and in this way, it allows obtaining the reflectance data of each one to assess Your match level. The following example shows two samples that coincide under daylight but not under incandescent light.

Although, during the tests with these techniques, various lighting sources are used, “daylight” can be considered as the priority when comparing colors, because beyond being the one that is commonly used, its spectrum contains "All colors" (visible wavelengths) with a highly uniform distribution, which allows a better and correct appreciation of the colors.

To conclude, it is necessary to mention that there is a very similar phenomenon called “color inconstancy” that can be confused with metamerism since it has the same base as this one, however, it only comes with a single color sample that is perceived differently depending on the type of light, unlike the metamerism that necessarily involves two or more samples.