ultraviolet radiation


ultraviolet radiation
Portion of the electromagnetic spectrum extending from the violet end of visible light to the X-ray region.

Ultraviolet (UV) radiation lies between wavelengths of about 400 nanometres and 10 nanometres, corresponding to frequencies of 7.5/n×/n1014 Hz to 3 × 1016 Hz. Most UV rays from the Sun are absorbed by the Earth's ozone layer. UV has low penetrating power, so its effects on humans are limited to the skin. These effects include stimulation of production of vitamin D, sunburn, suntan, aging signs, and carcinogenic changes. UV radiation is also used to treat jaundice in newborns, to sterilize equipment, and to produce artificial light.

* * *

      that portion of the electromagnetic spectrum extending from the violet, or short-wavelength, end of the visible light range to the X-ray region. Ultraviolet (UV) radiation is undetectable by the human eye, although, when it falls on certain materials, it may cause them to fluoresce—i.e., emit electromagnetic radiation of lower energy, such as visible light. Many insects, however, are able to see ultraviolet radiation.

      Ultraviolet radiation lies between wavelengths of about 400 nanometres (1 nanometre [nm] is 10−9 metre) on the visible-light side and about 10 nm on the X-ray side, though some authorities extend the short-wavelength limit to 4 nm. In physics, ultraviolet radiation is traditionally divided into four regions: near (400–300 nm), middle (300–200 nm), far (200–100 nm), and extreme (below 100 nm). In biology, three conventional divisions have been observed: near (400–315 nm), which is absorbed relatively poorly by organisms; actinic (315–200 nm), which is absorbed most readily by organic matter and thus has the greatest effects on organisms; and vacuum (less than 200 nm), which is absorbed by most substances, including oxygen in the air (and below 100 nm nitrogen), and so is of little use in biological experimentation. Based on the interaction of wavelengths of ultraviolet radiation with biological materials, three divisions have been designated: UVA (400–315 nm), also called black light; UVB (315–280 nm), responsible for the radiation's best-known effects on organisms; and UVC (280–100 nm), which does not reach the Earth's surface.

      Ultraviolet radiation is produced by high-temperature surfaces, such as the Sun, in a continuous spectrum and by atomic excitation in a gaseous discharge tube as a discrete spectrum of wavelengths. Most of the ultraviolet radiation in sunlight is absorbed by oxygen in the Earth's atmosphere, which forms the ozone layer of the lower stratosphere. Of the ultraviolet that does reach the Earth's surface, almost 99 percent is UVA radiation. When the ozone layer becomes thin, more UVB radiation reaches the Earth's surface and may have hazardous effects on organisms.

      Unlike X-rays, ultraviolet radiation has a low power of penetration; hence, its direct effects on the human body are limited to the surface skin. The direct effects include reddening of the skin (sunburn), pigmentation development (suntan), aging, and carcinogenic changes. Ultraviolet sunburns can be mild, causing only redness and tenderness, or they can be so severe as to produce blisters, swelling, seepage of fluid, and sloughing of the outer skin. The blood capillaries (minute vessels) in the skin dilate with aggregations of red and white blood cells to produce the red coloration. Tanning is a natural body defense relying on melanin to help protect the skin from further injury. Melanin is a chemical pigment in the skin that absorbs ultraviolet radiation and limits its penetration into tissues. A suntan occurs when melanin pigments in cells in the deeper tissue portion of the skin are activated by ultraviolet radiation, and the cells migrate to the surface of the skin. When these cells die, the pigmentation disappears. Persons of light complexion have less melanin pigment and so experience the harmful effects of ultraviolet radiation to a greater degree. The application of sunscreen to the skin can help to block absorption of ultraviolet radiation in such persons.

      Constant exposure to the Sun's ultraviolet radiation induces most of the skin (skin disease) changes commonly associated with aging, such as wrinkling, thickening, and changes in pigmentation. There is also a much higher frequency of skin cancer, particularly in persons with fair skin. The three basic skin cancers, basal- and squamous-cell carcinoma and melanoma, have been linked to long-term exposure to ultraviolet radiation and probably result from changes generated in the DNA of skin cells by ultraviolet rays.

      Ultraviolet radiation also has positive effects on the human body, however. It stimulates the production of vitamin D in the skin and can be used as a therapeutic agent for such diseases as psoriasis. Because of its bactericidal capabilities at wavelengths of 260–280 nm, ultraviolet radiation is useful as both a research tool and a sterilizing technique. Fluorescent lamps (fluorescent lamp) exploit the ability of ultraviolet radiation to interact with materials known as phosphors that emit visible light; compared with incandescent lamps (incandescent lamp), fluorescent lamps are a more energy-efficient form of artificial lighting.

* * *


Universalium. 2010.

Look at other dictionaries:

  • Ultraviolet radiation — Invisible rays that are part of the energy that comes from the sun. Ultraviolet radiation can burn the skin and cause skin cancer. Ultraviolet radiation is made up of three types of rays ultraviolet A, ultraviolet B, and ultraviolet C. Although… …   Medical dictionary

  • ultraviolet radiation — ultravioletinė spinduliuotė statusas T sritis Standartizacija ir metrologija apibrėžtis Optinės spinduliuotės trumpųjų bangų sritis nuo 10 nm iki 400 nm. atitikmenys: angl. ultraviolet radiation; UV radiation vok. ultraviolette Strahlung, f;… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • ultraviolet radiation — ultravioletinė spinduliuotė statusas T sritis fizika atitikmenys: angl. ultraviolet radiation; ultra violet rays; UV radiation vok. ultraviolette Strahlen, m; Ultraviolettstrahlung, f; UV Strahlung, f rus. ультрафиолетовое излучение, n;… …   Fizikos terminų žodynas

  • ultraviolet radiation — ultravioletinė Saulės spinduliuotė statusas Aprobuotas sritis hidrometeorologija apibrėžtis Akiai nematoma Saulės spinduliuotės spektro dalis, esanti tarp violetinių ir rentgeno spindulių. atitikmenys: angl. ultraviolet radiation vok.… …   Lithuanian dictionary (lietuvių žodynas)

  • ultraviolet radiation — ultravioletinė spinduliuotė statusas T sritis Energetika apibrėžtis Elektromagnetinės bangos, trumpesnės už regimąją šviesos bangą ir ilgesnės nei 10 nm. atitikmenys: angl. ultraviolet radiation vok. Ultraviolettstrahlung, f rus. ультрафиолетовое …   Aiškinamasis šiluminės ir branduolinės technikos terminų žodynas

  • ultraviolet radiation — ultravioletinė spinduliuotė statusas T sritis ekologija ir aplinkotyra apibrėžtis Optinės spinduliuotės trumpųjų bangų sritis nuo 10 nm iki 400 nm. Jos spektras yra tarp regimosios šviesos bangų ir rentgeno spindulių. Saulės šviesos spektre ji… …   Ekologijos terminų aiškinamasis žodynas

  • ultraviolet radiation — noun radiation lying in the ultraviolet range; wave lengths shorter than light but longer than X rays (Freq. 2) • Syn: ↑ultraviolet, ↑ultraviolet light, ↑ultraviolet illumination, ↑UV • Derivationally related forms: ↑ultraviolet …   Useful english dictionary

  • ultraviolet radiation — Invisible rays that are part of the energy that comes from the sun. UV radiation also comes from sun lamps and tanning beds. UV radiation can damage the skin and cause melanoma and other types of skin cancer. UV radiation that reaches the Earth s …   English dictionary of cancer terms

  • Ultraviolet radiation — Ультрафиолетовое излучение …   Краткий толковый словарь по полиграфии

  • ultraviolet-radiation measuring instrument — ultravioletinės spinduliuotės intensyvumo matuoklis statusas T sritis Standartizacija ir metrologija apibrėžtis Įtaisas ultravioletinės spinduliuotės intensyvumui matuoti. atitikmenys: angl. ultraviolet radiation measuring instrument vok.… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.