invisible short-wavelength radiation beyond the violet end of the visible spectrum. Sunlight contains ultraviolet rays, which are responsible for the production of both suntan and - on overexposure - sunburn. The dust and gases of the earth's atmosphere absorb most of the ultraviolet rays in sunlight (see ozone). If this did not happen, the intense ultraviolet radiation from the sun would be lethal to living organisms.
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invisible rays that are just beyond the violet end of the visible spectrum; their wavelengths range between 4 and 400 nm; see ultraviolet.Medical dictionary. 2011.