Several solid-state and vacuum devices have been explored for use in different parts of the UV spectrum. Strongly absorbed by atmospheric oxygen, though 150–200 nm wavelengths can propagate through nitrogen. Ionizing radiation at shorter wavelengths.Įntirely ionizing radiation by some definitions completely absorbed by the atmosphere. Short-wave UV, germicidal UV, ionizing radiation at shorter wavelengths, completely absorbed by the ozone layer and atmosphere: hard UV. Medium-wave UV, mostly absorbed by the ozone layer: intermediate UV Dorno radiation. Long-wave UV, blacklight, not absorbed by the ozone layer: soft UV. The electromagnetic spectrum of ultraviolet radiation (UVR), defined most broadly as 10–400 nanometers, can be subdivided into a number of ranges recommended by the ISO standard ISO 21348: Name The discovery of the ultraviolet radiation with wavelengths below 200 nm, named "vacuum ultraviolet" because it is strongly absorbed by the oxygen in air, was made in 1893 by German physicist Victor Schumann. In 1960, the effect of ultraviolet radiation on DNA was established. By 1903, the most effective wavelengths were known to be around 250 nm. In 1878, the sterilizing effect of short-wavelength light by killing bacteria was discovered. The terms "chemical rays" and "heat rays" were eventually dropped in favor of ultraviolet and infrared radiation, respectively. The simpler term "chemical rays" was adopted soon afterwards, and remained popular throughout the 19th century, although some said that this radiation was entirely different from light (notably John William Draper, who named them "tithonic rays" ). He called them "(de-)oxidizing rays" ( German: de-oxidierende Strahlen) to emphasize chemical reactivity and to distinguish them from " heat rays", discovered the previous year at the other end of the visible spectrum. 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. Ultraviolet has a higher frequency (thus a shorter wavelength) than violet light. "Ultraviolet" means "beyond violet" (from Latin ultra, "beyond"), violet being the color of the highest frequencies of visible light. Insects, birds, and some mammals can see near-UV (NUV) (i.e., slightly shorter wavelengths than what humans can see). The lower wavelength limit of human vision is conventionally taken as 400 nm, so ultraviolet rays are invisible to humans, although people can sometimes perceive light at shorter wavelengths than this. The UV spectrum, thus, has effects both beneficial and harmful to life. However, ultraviolet light (specifically, UVB) is also responsible for the formation of vitamin D in most land vertebrates, including humans. More energetic, shorter-wavelength "extreme" UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground. The amount of UV light produced by the Sun means that the Earth would not be able to sustain life on dry land if most of that light were not filtered out by the atmosphere. For humans, suntan and sunburn are familiar effects of exposure of the skin to UV light, along with an increased risk of skin cancer. Short-wave ultraviolet light damages DNA and sterilizes surfaces with which it comes into contact. These interactions can involve absorption or adjusting energy states in molecules, but do not necessarily involve heating. Many practical applications, including chemical and biological effects, derive from the way that UV radiation can interact with organic molecules. 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. It is also produced by electric arcs, Cherenkov radiation, and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. Ultraviolet ( UV) is a form of electromagnetic radiation with wavelength shorter than that of visible light, but longer than X-rays. Arc welders must wear eye protection and cover their skin to prevent photokeratitis and serious sunburn. UV radiation is also produced by electric arcs.
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