Ultraviolet

Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency of approximately 30 PHz) to 400 nm (750 THz), shorter than that of visible light but longer than X-rays. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionize atoms, it can cause chemical reactions and causes many substances to glow or fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules.

Sources

Sunlight is the primary source of UV radiation. Artificial sources include tanning beds, black lights, curing lamps, germicidal lamps, mercury vapor lamps, halogen lights, fluorescent and incandescent sources, and some types of lasers.

Effects on health

Exposure to UV radiation can cause photokeratitis (a painful eye condition), skin aging, skin cancer, and can suppress the immune system. UV can also sterilize and can be used to make drinking water safe.

Measurement and protection

UV can be measured using a UV meter. Protection against UV radiation includes wearing sunglasses and sun protective clothing, applying sunscreen, and staying out of the sun during peak hours.

See also

• Infrared
• Visible spectrum
• X-ray

Ultraviolet Resources
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