ULTRAVIOLET

Electromagnetic radiation that has a wavelength shorter than visible light and longer than x-rays. Although it accounts for only 4 to 5 percent of the total energy of insolation, it is responsible for many complex photochemical reactions, such as fluorescence and the formation of ozone.

Electromagnetic radiation with wavelengths between that of visible violet light and X-rays; it ranges from 400 to 4 nanometers. Ultraviolet is subdivided into near (NUV) 400 to 300 nanometers, far (FUV) 300 to 200 nanometers, extreme (XUV) 200 to 100 nanometers, and vacuum (VUV) 100 to 4 nanometers. Most of the potentially hazardous UV radiation emitted by the Sun is absorbed by the ozone layer. [See also radiation.] updraft A rising air current.