Why does ultraviolet light cause color to fade?

    Because of photodegradation.

It is all about the chemical makeup of an object. The technical term for color fading is photodegradation. There are light absorbing color bodies called chromophores that are present in dyes. The color(s) we see are based upon these chemical bonds and the amount of light that is absorbed in a particular wavelength.

Ultraviolet rays can break down the chemical bonds and thus fade the color(s) in an object - it is a bleaching effect. Some objects may be more prone to fading, such as dyed textiles and watercolors. Other objects may reflect the light more, which makes them less prone to fade.

Related Web Sites

The Chemistry of Fading - This site, from Waxahachie High School in Waxahachie, Texas, discusses the chemical processes involved in fading caused by ultraviolet light. Light and Color - The Franklin Institute- This site provides an introduction to how we see color. Northeast Document Conservation Center. Preservation Leaflet: Protection from Light Damage - NEDCC’s Field Service department provides free preservation advice on protecting your library and archival material from light damage.

Further Reading

Nassau, Kurt. The Physics and chemistry of color: the fifteen causes of color. New York: Wiley, 2001. 481 p. .

For more print resources...
Search on "Color," "Dyes and dyeing chemistry," or "Light" in the Library of Congress Online Catalog.

What is ultraviolet light? From "Ultraviolet: the Science Behind the Medicine." ClarionHEALTH, c2000.

Of the three types of energy contained in sunlight--ultraviolet radiation, visible light, and infrared radiation--ultraviolet (UV) can be the most dangerous. From "Cool in the Shade," Texas A&M University.

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