Ultraviolet radiation is an electromagnetic radiation in the wavelength interval between x-rays and visible Light, i.e. from about 5 nanometers (nm) to about 400 nm. Ultraviolet (UV) radiation was discovered in 1801 by the German physicist, Johann Wilhelm Ritter, who found that the radiation outside the violet end of the visible solar spectrum could decompose silver chloride (AgCl).
Physiologically, ultraviolet radiation is extremely powerful, producing sunburn and causing the formation of vitamin D in the skin. Ultraviolet radiation is invisible, but can be harmful to the human eye.
Together with other kinds of radiation, UV radiation is generated by the Sun. The ultraviolet radiation in sunlight is divided into three bands: UV-A (320-400 nm), which can cause skin damage and may cause melanomatous skin cancer; UV-B (280-320 nm), stronger radiation that increases in the summer and is a common cause of sunburn and most common skin cancer; and UV-C (below 280 nm), the strongest and potentially most harmful form.
Much UV-B and most UV-C radiation is absorbed by the ozone layer of the atmosphere before it can reach the earth's surface; the depletion of this layer is increasing the amount of ultraviolet radiation that can pass through it. The radiation that does pass through is largely absorbed by ordinary window glass or impurities in the air (e.g., water, dust, and smoke) or is screened by clothing.