Ultraviolet (UV) light represents one portion of the sun's electromagnetic spectrum. It is the wavelength shorter than that of visible light, but longer than x-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV.
It is so named because the spectrum consists of electromagnetic waves with frequencies higher than those that humans identify as the color violet. Most people are aware of the effects of UV through sunburn, but the UV spectrum has many other practical uses in business, government, and industry.
Ultraviolet light is produced naturally by the sun with a fair amount of UVA reaching the earth's surface. UV light can be produced by a number of sources such as photocopiers & arc-welders. Manufactured light sources can include LED's, arc lamps and microwave lamps.