ultraviolet

Denoting electromagnetic rays at higher frequency than the violet end of the visible spectrum.

- u. A (UVA) u. radiation from 320 to 400 nm that causes skin tanning but is very weakly sunburn-producing and carcinogenic.

- u. B (UVB) u. radiation from 290 to 320 nm that most effectively causes sunburning and tanning; excessive UVB exposure is a cause of cancer of fair skin.

- u. C u. radiation from 200 to 290 nm; UVC in sunlight does not reach the surface of the earth; germicidal and mercury arc lamps may cause sunburn and photokeratitis.

- extravital u. having wavelengths of 2900 to 1850 Å.

- intravital u. having wavelengths of 3900 to 3200 Å.

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ul·tra·vi·o·let .əl-trə-'vī-(ə-)lət adj

1) situated beyond the visible spectrum at its violet end used of radiation having a wavelength shorter than wavelengths of visible light and longer than those of X-rays

2) relating to, producing, or employing ultraviolet radiation

ultraviolet n ultraviolet radiation

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ul·tra·vi·o·let (ul″trə-viґə-lət) beyond the violet end of the spectrum; said of electromagnetic rays or radiation between the violet rays and the x-rays, that is, with wavelengths between 200 and 400 nm. These rays have powerful actinic and chemical properties, inducing sunburn and tanning of the skin and producing ergocalciferol (vitamin D₂) by their action on ergosterol in the skin.