Why are different things different colors?

(Lansing State Journal, May 4, 1994)

When different wavelengths of light hit our eyes, we see different colors.

Light from the sun or light bulbs has many different wavelengths. This great mixture of wavelengths is commonly perceived as white. If the light hits an object - a road, tree, house, anything really - the object absorbs some wavelengths. Other wavelengths are reflected, and those are the ones we see.

When an object absorbs all wavelengths to a great extent, it appears black. If it largely reflects all light, it appears white. Objects that absorb only a fraction of all the wavelengths appear colored.

You can think of these phenomena in terms of the analogy: Light falling on an object is somewhat like rain falling on the ground. During a thunderstorm, some raindrops are quickly absorbed into the earth, but others hit so hard and fast they bounce off the ground.

Different materials absorb different wavelengths of light. Things that absorb light in the visible spectrum are called pigments. The chemical structure of each pigment determines which wavelengths of light it can absorb, and which are reflected.

Examples of pigments are: heme, which gives blood a red color; melanin, which gives skin a brown color; and chlorophyll, which makes plants green. Each of these compounds has a different chemical structure that absorbs different wavelengths of light, and thus, appear different in color.

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