Definition: Ultra-violet: radiation whose wavelength is shorter than violet -- i.e. outside range of human vision -- to X-rays. * Near UV: 400-300nm; middle UV: 300-200nm; far or extreme UV: 200nm or less. * Highly active, however: it is used in photography to harden or cure emulsions e.g. in photomechanical processes, to dry printing ink, to make exposures e.g. platinum printing and in flourescence photography. * UV can be seen by many insects and it affects human skin e.g. to give tans.

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