ultraviolet (UV) radiation Electromagnetic waves * in the wavelength 4 nm to 400 nm, extending from violet limit of visibility to long X rays (see Appendix-V). It is divided into three regions, near, from 400 nm to 300 nm, far, from 300 nm to 200 nm, and extreme, below 200 nm. The extreme region is absorbed strongly by air. UV source in the laboratory is mercury vapor lamp, without the phosphor coating and made of special glass that transmits these radiations. Sun is a source of UV radiation, although much of the solar UV radiation is absorbed in the ozone layer of the upper atmosphere. The fluorescent pigments in paints and dyes absorb these radiations and reradiate in the optical wavelengths.

UV radiations carry higher energy than visible light, because they are of shorter wavelengths. UV radiations cannot penetrate beyond the skin’s outer layer. Excess exposure of UV radiation damages the skin and may even lead to cancer of the skin.