Ultraviolet Light
Next in frequency comes ultraviolet (UV). The wavelength of UV rays is shorter than the violet end of the visible spectrum but longer than the X-ray.
UV in the very shortest range (next to X-rays) is capable even of ionizing atoms (see photoelectric effect), greatly changing their physical behavior.
At the middle range of UV, UV rays cannot ionize but can break chemical bonds, making molecules to be unusually reactive. Sunburn, for example, is caused by the disruptive effects of middle range UV radiation on skin cells, which is the main cause of skin cancer. UV rays in the middle range can irreparably damage the complex DNA molecules in the cells producing thymine dimers making it a very potent mutagen.
The Sun emits significant UV radiation (about 10% of its total power), including extremely short wavelength UV that could potentially destroy most life on land (ocean water would provide some protection for life there). However, most of the Sun's most-damaging UV wavelengths are absorbed by the atmosphere's oxygen, nitrogen, and ozone layer before they reach the surface. The higher ranges of UV (vacuum UV) are absorbed by nitrogen and, at longer wavelengths, by simple diatomic oxygen in the air. Most of the UV in this mid-range is blocked by the ozone layer, which absorbs strongly in the important 200–315 nm range, the lower part of which is too long to be absorbed by ordinary dioxygen in air. The range between 315 nm and visible light (called UV-A) is not blocked well by the atmosphere, but does not cause sunburn and does less biological damage. However, it is not harmless and does cause oxygen radicals, mutation and skin damage. See ultraviolet for more information.
Read more about this topic: Electromagnetic Spectrum, Types of Radiation
Famous quotes containing the words ultraviolet and/or light:
“As if the musicians did not so much play the little phrase as execute the rites required by it to appear, and they proceeded to the necessary incantations to obtain and prolong for a few instants the miracle of its evocation, Swann, who could no more see the phrase than if it belonged to an ultraviolet world ... Swann felt it as a presence, as a protective goddess and a confidante to his love, who to arrive to him ... had clothed the disguise of this sonorous appearance.”
—Marcel Proust (1871–1922)
“When you take a light perspective, it’s easier to step back and relax when your child doesn’t walk until fifteen months, . . . is not interested in playing ball, wants to be a cheerleader, doesn’t want to be a cheerleader, has clothes strewn in the bedroom, has difficulty making friends, hates piano lessons, is awkward and shy, reads books while you are driving through the Grand Canyon, gets caught shoplifting, flunks Spanish, has orange and purple hair, or is lesbian or gay.”
—Charlotte Davis Kasl (20th century)