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[[File:lighterstill.jpg]][[File:Ultraviolet.jpg|right|frame]]
==Origin==
The name means "beyond violet" (from [[Latin]] ultra, "beyond"), violet being the [[color]] of the shortest [[wavelengths]] of visible [[light]]. UV light has a shorter wavelength than violet light.
*[http://en.wikipedia.org/wiki/19th_century 1840]
==Definition==
*1: situated beyond the visible [[spectrum]] at its [[violet]] end —used of [[radiation]] having a [[wavelength]] shorter than wavelengths of visible [[light]] and longer than those of [http://en.wikipedia.org/wiki/x-ray X-rays]
==Description==
'''Ultraviolet''' (UV) [[light]] is [[electromagnetic]] [[radiation]] with a [[wavelength]] shorter than that of visible light, but longer than [https://en.wikipedia.org/wiki/X-ray X-rays], that is, in the range between 400 nm and 10 nm, corresponding to photon energies from 3 eV to 124 eV. It is so-named because the spectrum consists of electromagnetic waves with [[frequencies]] higher than those that humans identify as the color [[violet]]. These frequencies are invisible to most humans except those with [https://en.wikipedia.org/wiki/Aphakia aphakia]. Near-UV is visible to a number of insects and birds.
UV light is found in [[sunlight]] and is emitted by [https://en.wikipedia.org/wiki/Electric_arc electric arcs] and specialized lights such as mercury lamps and [https://en.wikipedia.org/wiki/Black_light black lights]. It can cause chemical reactions, and causes many substances to glow or fluoresce. A large fraction of UV, including all that reaches the surface of the [[Earth]], is classified as [https://en.wikipedia.org/wiki/Non-ionizing_radiation non-ionizing radiation]. The higher energies of the ultraviolet spectrum from wavelengths about 120 nm to 10 nm ('extreme' ultraviolet) are [https://en.wikipedia.org/wiki/Ionizing_radiation ionizing], but, due to this effect, these wavelengths are [[absorbed]] by nitrogen and even more strongly by [https://en.wikipedia.org/wiki/Dioxygen dioxygen], and thus have an extremely short path length through air. However, the entire spectrum of ultraviolet radiation has some of the [[biological]] features of ionizing radiation: It does far more damage to many [[molecules]] in biological systems than is accounted for by simple [[heating]] effects (an example is [https://en.wikipedia.org/wiki/Sunburn sunburn]). These properties derive from the ultraviolet photon's power to alter [https://en.wikipedia.org/wiki/Chemical_bond chemical bonds] in molecules, even without having enough energy to ionize [[atoms]].
Although ultraviolet radiation is [[invisible]] to the human eye, most people are aware of the [[effect]] it has on the skin of fair-skinned people, i.e., the suntan and sunburn. Normal human skin responds to [[exposure]] to small doses of this kind of [[radiation]] by increasing the amount of protective [https://en.wikipedia.org/wiki/Melanin melanin] in the skin's outer layers; too much of this radiation in too short a period of time, however, results in cellular damage from radiation burn. In fact, the damaging effects of short-wavelength and mid-wavelength UV means that life on Earth outside of the deep oceans is possible only because the [[atmosphere]], primarily the [https://en.wikipedia.org/wiki/Ozone_layer ozone layer], filters out the vast majority of this light. A small amount of the shorter wavelength ultraviolet reaches the surface, which causes sunburn, long-term skin damage, and skin cancer. Ultraviolet is also responsible for the formation of [https://en.wikipedia.org/wiki/Vitamin_D vitamin D] in organisms that make this vitamin (including humans). The UV spectrum thus has many effects, both beneficial and damaging, to human [[health]].[https://en.wikipedia.org/wiki/Ultraviolet]
[[Category: Chemistry]]
[[Category: Physics]]
==Origin==
The name means "beyond violet" (from [[Latin]] ultra, "beyond"), violet being the [[color]] of the shortest [[wavelengths]] of visible [[light]]. UV light has a shorter wavelength than violet light.
*[http://en.wikipedia.org/wiki/19th_century 1840]
==Definition==
*1: situated beyond the visible [[spectrum]] at its [[violet]] end —used of [[radiation]] having a [[wavelength]] shorter than wavelengths of visible [[light]] and longer than those of [http://en.wikipedia.org/wiki/x-ray X-rays]
==Description==
'''Ultraviolet''' (UV) [[light]] is [[electromagnetic]] [[radiation]] with a [[wavelength]] shorter than that of visible light, but longer than [https://en.wikipedia.org/wiki/X-ray X-rays], that is, in the range between 400 nm and 10 nm, corresponding to photon energies from 3 eV to 124 eV. It is so-named because the spectrum consists of electromagnetic waves with [[frequencies]] higher than those that humans identify as the color [[violet]]. These frequencies are invisible to most humans except those with [https://en.wikipedia.org/wiki/Aphakia aphakia]. Near-UV is visible to a number of insects and birds.
UV light is found in [[sunlight]] and is emitted by [https://en.wikipedia.org/wiki/Electric_arc electric arcs] and specialized lights such as mercury lamps and [https://en.wikipedia.org/wiki/Black_light black lights]. It can cause chemical reactions, and causes many substances to glow or fluoresce. A large fraction of UV, including all that reaches the surface of the [[Earth]], is classified as [https://en.wikipedia.org/wiki/Non-ionizing_radiation non-ionizing radiation]. The higher energies of the ultraviolet spectrum from wavelengths about 120 nm to 10 nm ('extreme' ultraviolet) are [https://en.wikipedia.org/wiki/Ionizing_radiation ionizing], but, due to this effect, these wavelengths are [[absorbed]] by nitrogen and even more strongly by [https://en.wikipedia.org/wiki/Dioxygen dioxygen], and thus have an extremely short path length through air. However, the entire spectrum of ultraviolet radiation has some of the [[biological]] features of ionizing radiation: It does far more damage to many [[molecules]] in biological systems than is accounted for by simple [[heating]] effects (an example is [https://en.wikipedia.org/wiki/Sunburn sunburn]). These properties derive from the ultraviolet photon's power to alter [https://en.wikipedia.org/wiki/Chemical_bond chemical bonds] in molecules, even without having enough energy to ionize [[atoms]].
Although ultraviolet radiation is [[invisible]] to the human eye, most people are aware of the [[effect]] it has on the skin of fair-skinned people, i.e., the suntan and sunburn. Normal human skin responds to [[exposure]] to small doses of this kind of [[radiation]] by increasing the amount of protective [https://en.wikipedia.org/wiki/Melanin melanin] in the skin's outer layers; too much of this radiation in too short a period of time, however, results in cellular damage from radiation burn. In fact, the damaging effects of short-wavelength and mid-wavelength UV means that life on Earth outside of the deep oceans is possible only because the [[atmosphere]], primarily the [https://en.wikipedia.org/wiki/Ozone_layer ozone layer], filters out the vast majority of this light. A small amount of the shorter wavelength ultraviolet reaches the surface, which causes sunburn, long-term skin damage, and skin cancer. Ultraviolet is also responsible for the formation of [https://en.wikipedia.org/wiki/Vitamin_D vitamin D] in organisms that make this vitamin (including humans). The UV spectrum thus has many effects, both beneficial and damaging, to human [[health]].[https://en.wikipedia.org/wiki/Ultraviolet]
[[Category: Chemistry]]
[[Category: Physics]]
