ultraviolet (UV)

A Sanax 15W "black light" bulb. It emits mostly near UV with very little visible light. Image source: Wikipedia

Electromagnetic radiation beyond the violet end of the visible spectrum with wavelengths approximately in the range 10–400 nanometers (100 Å to 4,000 Å). The ultraviolet (UV) spectrum can be subdivided in a number of ways. The near ultraviolet (the long wavelength end of the range) extends from just beyond the violet end of the visible spectrum to about 300 nm (3,000 Å). The far ultraviolet stretches from 200 nm to the Lyman limit (see Lyman series) at 91.2 nm (912 Å). Beyond this, from the Lyman limit to the start of the X-ray regime at about 10 nm (100 Å), lies the extreme ultraviolet. Much ultraviolet light from the Sun is absorbed by the ozone layer.

The draft ISO standard on determining solar irradiances (ISO-DIS-21348) describes the ranges listed in the table below.

ISO solar irradiance categories
name	wavelength range
ultraviolet A (UVA)	315–400 nm
near ultraviolet (NUV)	300–400 nm
ultraviolet B (UVB)	280–315 nm
middle ultraviolet (MUV)	200–300 nm
ultraviolet C (UVC)	100–280 nm
far ultraviolet (FUV)	122–200 nm
vacuum ultraviolet (VUV)	10–200 nm
extreme ultraviolet (EUV)	10–121 nm

Health-related effects of UV

The ultraviolet light (mainly UVA) that reaches the Earth's surface causes tanning and the production of vitamin D in the skin. It can also have harmful effects, such as skin cancer. This form of light is generated by tanning beds and booths to produce a suntan. Tanning beds are designed to emit only UVA rays; however, in practise they also emit some UVB, which is more likely to causing burning and skin cancer.

Ultraviolet light is also produced by welding torches, carbon arc lamps, and some lasers. Special precautions, such as the use of goggles, should always be taken when using such equipment.

UV light is sometimes used in phototherapy to treat skin disorders such as eczema, psoriasis, and jaundice in newborn babies.

Related category

• WAVES AND WAVE PHENOMENA

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