Ultraviolet radiation

Posted: 22 August 2000

High energy, short-wave radiation lying between visible light and X-rays in the electromagnetic spectrum. It is usually divided into ultraviolet-A (UV-A) with wavelengths of 320-400 nanometres (nm), ultraviolet-B (UV-B) with wavelengths of 280-320nm and ultraviolet-C (UV-C) with wavelengths of 200-280nm. Ultraviolet rays are an important component of solar radiation. At normal levels it is an important germicide and is essential for the synthesis of Vitamin D in humans. At elevated levels, it causes sunburn and skin cancer, and can produce changes in the genetic make-up of organisms. It also has a role in the formation of photochemical smog. Most of the UV radiation which reaches the earth from the sun is absorbed by the ozone layer in the stratosphere. Thinning of the ozone layer, however, has increased the proportion of ultraviolet radiation - particularly UV-B - reaching the earth's surface, giving rise to fears of an increasing incidence of skin cancer and other radiation-related problems.