Infrared Rays

Infrared rays, often called heat rays, resemble light rays, but they cannot be seen by the human eye. They behave similarly to light rays in reflection and refraction (see Light).

Any object, such as a chair, gives off infrared rays in relation to its temperature. As an object gets hotter, it gives off more and more infrared rays. Such systems as the Forward-Looking Infrared (FLIR) system, which was developed in the 1970's, can detect infrared rays from objects and record variations in their temperatures. Individuals using these systems can "see" objects in the dark or through fog.

Photographers use film that is sensitive to infrared rays to take pictures in places where there is no visible light. Doctors use infrared lamps to treat skin diseases and sore muscles. In these treatments, the infrared rays pass through the patient's skin and produce heat when they strike the affected area.

Infrared waves lie just beyond the red end of the visible light spectrum. Sir William Herschel, a British astronomer, discovered infrared rays in 1800 by observing the effect of the heat they produced.

Contributor: Gerald Feinberg, Ph.D., Former Prof. of Physics, Columbia Univ.

Infrared Rays

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