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Applications

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Because of its ability to cause chemical reactions and excite fluorescence in materials, ultraviolet radiation has a number of applications. The following table gives some uses of specific wavelength bands in the UV spectrum 13.5 nm : Extreme ultraviolet lithography 30–200 nm : Photoionization, ultraviolet photoelectron spectroscopy, standard integrated circuit manufacture by photolithography 230–365 nm : UV-ID, label tracking, barcodes 230–400 nm : Optical sensors, various instrumentation 240–280 nm : Disinfection, decontamination of surfaces and water (DNA absorption has a peak at 260 nm), germicidal lamps 200–400 nm : Forensic analysis, drug detection 270–360 nm : Protein analysis, DNA sequencing, drug discovery 280–400 nm : Medical imaging of cells 300–320 nm : Light therapy in medicine 300–365 nm : Curing of polymers and printer inks 350–370 nm : Bug zappers (flies are most attracted to light at 365 nm) Photography edit Photographic film responds to ultraviolet radiation
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Solar ultraviolet

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Very hot objects emit UV radiation (see black-body radiation). The Sun emits ultraviolet radiation at all wavelengths, including the extreme ultraviolet where it crosses into X-rays at 10 nm. Extremely hot stars emit proportionally more UV radiation than the Sun. Sunlight in space at the top of Earth's atmosphere (see solar constant) is composed of about 50% infrared light, 40% visible light, and 10% ultraviolet light, for a total intensity of about 1400 W/m2 in vacuum. The atmosphere blocks about 77% of the Sun's UV, when the Sun is highest in the sky (at zenith), with absorption increasing at shorter UV wavelengths. At ground level with the sun at zenith, sunlight is 44% visible light, 3% ultraviolet, and the remainder infrared. Of the ultraviolet radiation that reaches the Earth's surface, more than 95% is the longer wavelengths of UVA, with the small remainder UVB. Almost no UVC reaches the Earth's surface. The fraction of UVB which remains in UV radiation after pas
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