ultraviolet radiation

Electromagnetic radiation of wavelengths from about 400 to 10 nanometres (where the X-ray range begins). Physiologically, ultraviolet (UV) radiation is extremely powerful, producing sunburn and causing the formation of vitamin D in the skin. UV radiation is invisible to the human eye, but its effects can be demonstrated.

The stratospheric ozone layer shields us from much of the UV radiation of the Sun, particularly the more dangerous, high-energy parts of the UV spectrum. Due to the loss of ozone in the 20th century, levels of UV radiation have risen an average of 6.8% a decade in the northern hemisphere and 9.9% in the southern hemisphere 1972–96, according to data gathered by the Total Ozone Mapping Spectrometer on the Nimbus 7 satellite. UV rays are strongly germicidal and may be produced artificially by mercury vapour and arc lamps for therapeutic use. The radiation may be detected with ordinary photographic plates or films. It can also be studied by its fluorescent effect on certain materials. The desert iguana Disposaurus dorsalis uses it to locate the boundaries of its territory and to find food.