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"Ultraviolet" means "beyond violet" (from Latin ultra, "beyond"), violet being the color of the highest frequencies of visible light. Ultraviolet has a higher frequency than violet light.
UV radiation was discovered in 1801 when the German physicist Johann Wilhelm Ritter observed that invisible rays just beyond the violet end of the visible spectrum darkened silver chloride-soaked paper more quickly than violet light itself. He called them "oxidizing rays" to emphasize chemical reactivity and to distinguish them from "heat rays", discovered the previous year at the other end of the visible spectrum. The simpler term "chemical rays" was adopted shortly thereafter, and it remained popular throughout the 19th century, although there were those who held that these were an entirely different sort of radiation from light (notably John William Draper, who named them "tithonic rays"). The terms chemical and heat rays were eventually dropped in favour of ultraviolet and infrared radiation, respectively. In 1878 the effect of short-wavelength light on sterilizing bacteria was discovered. By 1903 it was known the most effective wavelengths were around 250 nm. In 1960, the effect of ultraviolet radiation on DNA was established.
The discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet because it is strongly absorbed by air, was made in 1893 by the German physicist Victor Schumann.
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 spectrum13.5 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)
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
300–400 nm: Solid-state lighting
350–370 nm: Bug zappers (flies are most attracted to light at 365 nm)
400-700 nm: Photosynthetically active radiation (Photosynthetic organisms are able to use this wavelength in the process of photosynthesis)