Ultraviolet Radiation
. Ultraviolet Radiation, electromagnetic radiation that has wavelengths in the range between 4000 angstrom units (Å), the wavelength of violet light, and 150 Å, the length of X rays. Natural ultraviolet radiation is produced principally by the sun . Ultraviolet radiation is produced artificially by electric-arc lamps. Ultraviolet radiation is often divided into three categories based on wavelength, UV-A, UV-B, and UV-C. In general shorter wavelengths of ultraviolet radiation are more dangerous to living organisms. UV-A has a wavelength from 4000 Å to about 3150 Å. UV-B occurs at wavelengths from about 3150 Å to about 2800 Å and causes sunburn; prolonged exposure to UV-B over many years can cause skin cancer. UV-C has wavelengths of about 2800 Å to 150 Å and is used to sterilize surfaces because it kills bacteria and viruses. The earth's atmosphere protects living organisms from the sun's ultraviolet radiation. If all the ultraviolet radiation produced by the sun were allowed ...