Colour Perception With Different Light Sources (Metamerism)

Colour is a dominant presence in our daily lives. From the clothes we wear to the food we eat, we are constantly viewing and evaluating colour. But how does light affect the colours we see? If you’ve ever noticed that your colour perception changes with different light sources, then you’ve experienced a vexing phenomenon known as metamerism.

What Is Metamerism?

Metamerism occurs when two colours match under one type of lighting but not another. This peculiarity has to do with the relationship between light and colour.

We perceive colour based on the way an object reflects light, and that perception is based on the light source. When you compare the reflectance of incandescent light to daylight, for example, you’ll find that incandescent light has a higher level of energy in the red area of the spectrum. This means an object viewed under incandescent light will appear redder than it will in daylight. Daylight has more energy on the opposite, blue end of the spectrum.

Reflectance information about a specific colour is known as that colour’s “fingerprint.” When two colours look identical under one light source, but different under another, they are known as a metameric pair.

What Causes Metamerism?

Metamerism is often caused by the use of different materials to assemble a product. In the auto industry, for example, manufacturers have to find ways to ensure the colours of a car’s different components “match” under all types of illumination, even though the paints used on the body have colour fingerprints that are completely different from the colour fingerprints of the dyes used for the dashboard.

Fabrics, paper products, paints, plastics, liquids and other materials that contain fluorescent optical brighteners are also more likely to experience metamerism. Fluorescent optical brighteners are synthetic chemicals that absorb ultraviolet energy and re-emit it at longer wavelengths to make the colour appear whiter and brighter. Because it can be difficult to properly manage optical brighteners during production runs, there is a higher chance of metameric pairs.

How Can You Prevent and Account for Metamerism?

Although it can be difficult to completely eliminate metamerism, there are some steps you can take to help prevent it and account for it:

• Evaluate colour under a variety of lighting conditions. Make sure they match under every possible condition.
• Set standard operating procedures. Clear protocols and expectations can help reduce the chance of metamerism, especially if you are dealing with different manufacturers and suppliers.
• Use a spectrophotometer. Spectrophotometers are precise scientific instruments that remove human subjectivity when it comes to communicating colour. They provide a three-dimensional numeric value (L*a*b* coordinates) to precisely define a colour, and they eliminate the challenge of viewing a colour under various light sources.

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