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 (UVC) 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.
vital u. rays necessary or helpful to normal growth; they promote calcium metabolism, are antirachitic in action, and have wavelengths between 3200 and 2900 Å.
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