Ultraviolet light

Invisible light from the part of the electromagnetic spectrum immediately beyond the violet end of the visible light spectrum. Long wavelength ultraviolet light is termed UVA, intermediate UVB, and short UVC. Ultraviolet light occurs in sunlight, but much of it is absorbed by the ozone layer. The ultraviolet light (mainly UVA) that reaches the earth’s surface causes the tanning effects of sunlight and the production of vitamin D in the skin. It can have harmful effects, such as skin cancer (see sunlight, adverse effects of). Ultraviolet light is sometimes used in phototherapy. A mercury-vapour lamp (Wood’s light) can also produce ultraviolet light. This is used to diagnose skin conditions such as tinea because it causes the infected area to fluoresce.


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