Ultraviolet. Background to the schools Wikipedia. This Wikipedia selection is available offline from SOS Children for distribution in the developing world. See http: //www. soschildren. False- colour image of the solar corona as seen in deep ultraviolet light at 1. Extreme ultraviolet Imaging Telescope instrument aboard the SOHO spacecraft. Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X- rays. It is named because the spectrum consists of refrangible electromagnetic waves with frequencies higher than those that humans identify as the colour violet. UV light is typically found as part of the radiation received by the Earth from the Sun. Most humans are aware of the effects of UV through the painful condition of sunburn. The UV spectrum has many other effects, including both beneficial and damaging changes to human health. Discovery. The discovery of UV radiation was intimately associated with the observation that silver salts darken when exposed to sunlight. In 1. 80. 1 the German physicist Johann Wilhelm Ritter made the hallmark observation that invisible rays just beyond the violet end of the visible spectrum were especially effective at darkening silver chloride- soaked paper. GAM UV protection film in rolls, sheets and tubes protects rare and precious documents, photographs, paintings, and fabrics from the destructive effects of. The terms chemical and heat rays were eventually dropped in favour of ultraviolet and infrared radiation, respectively. Origin of term. The name means . UV light has a shorter wavelength than that of violet light. Subtypes. The electromagnetic spectrum of ultraviolet light can be subdivided in a number of ways. The draft ISO standard on determining solar irradiances (ISO- DIS- 2. Name. Abbreviation Wavelength range in nanometers. Energy per photon. Ultraviolet A, long wave, or black light. UVA4. 00 nm – 3. 15 nm. VNear. NUV4. 00 nm – 3. VUltraviolet B or medium wave. UVB3. 15 nm – 2. 80 nm. VMiddle. MUV3. 00 nm – 2. Desde Septiembre de 1992 el Instituto Federal. Ultraviolet (UV) is an electromagnetic radiation with a wavelength from 10 nm (30 PHz) to 400 nm (750 THz), shorter than that of visible light but longer than X-rays. Explorador Ultravioleta Extremo (EUVE); Ultravioleta; 1992; NASA. 28) ASCA; Rayos X; 1993; ISAS y NASA. 29) Astro 2; Ultravioleta; 1993; NASA. VUltraviolet C, short wave, or germicidal. UVC2. 80 nm – 1. 00 nm. VFar. FUV2. 00 nm – 1. VVacuum. VUV2. 00 nm – 1. VExtreme EUV1. 21 nm – 1. VIn photolithography, in laser technology, etc., the term deep ultraviolet or DUV refers to wavelengths below 3. In the long- wave limit of this region, roughly 1. Work in this region can be performed in an oxygen free atmosphere, pure nitrogen being commonly used, which avoids the need for a vacuum chamber. See 1 E- 7 m for a list of objects of comparable sizes. Black light. A black light, or Wood's light, is a lamp that emits long wave UV radiation and very little visible light. Commonly these are referred to as simply a . Fluorescent black lights are typically made in the same fashion as normal fluorescent lights except that only one phosphor is used and the normally clear glass envelope of the bulb may be replaced by a deep- bluish- purple glass called Wood's glass, a nickel- oxide–doped glass, which blocks almost all visible light above 4. The colour of such lamps is often referred to in the trade as . The phosphor typically used for a near 3. Sr. B4. O7. F: Eu. Sr. B4. O7: Eu. 2+) while the phosphor used to produce a peak around 3. Ba. Si. 2O5: Pb+). Unlike UVB and UVC, which are responsible for the direct DNA damage that leads to skin cancer, black light is limited to lower energy, longer waves and does not cause sunburn. However, UVA is capable of causing damage to collagen fibers and destroying vitamin A in skin. A black light may also be formed by simply using Wood's glass instead of clear glass as the envelope for a common incandescent bulb. This was the method used to create the very first black light sources. Though it remains a cheaper alternative to the fluorescent method, it is exceptionally inefficient at producing UV light (a mere few lumens per watt) owing to the black body nature of the incandescent light source. Incandescent UV bulbs, due to their inefficiency, may also become dangerously hot during use. More rarely still, high power (hundreds of watts) mercury vapor black lights can be found which use a UV emitting phosphor and an envelope of Wood's glass. These lamps are used mainly for theatrical and concert displays and also become very hot during normal use. Some UV fluorescent bulbs specifically designed to attract insects for use in bug zappers use the same near- UV emitting phosphor as normal blacklights, but use plain glass instead of the more expensive Wood's glass. Plain glass blocks less of the visible mercury emission spectrum, making them appear light blue to the naked eye.
These lamps are referred to as . A positive effect of UVB exposure is that it induces the production of vitamin D in the skin. It has been estimated that tens of thousands of premature deaths occur in the United States annually from a range of cancers due to vitamin D deficiency. Another effect of vitamin D deficiency is osteomalacia (the adult equivalent of rickets), which can result in bone pain, difficulty in weight bearing and sometimes fractures. Other studies show most people get adequate Vitamin D through food and incidental exposure. Many countries have fortified certain foods with Vitamin D to prevent deficiency. Eating fortified foods or taking a dietary supplement pill is usually preferred to UVB exposure, due to the increased risk of skin cancer from UV radiation. Too little UVB radiation leads to a lack of Vitamin D. Too much UVB radiation leads to direct DNA damages and sunburn. An appropriate amount of UVB (What is appropriate depends on your skin colour) leads to a limited amount of direct DNA damage. This is recognized and repaired by the body. Then the melanin production is increased which leads to a long lasting tan. This tan occurs with a 2 day lag phase after irradiation, but it is much less harmful and long lasting than the one obtained from UVA. Ultraviolet radiation has other medical applications, in the treatment of skin conditions such as psoriasis and vitiligo. UVA radiation can be used in conjunction with psoralens ( PUVA treatment). UVB radiation is rarely used in conjunction with psoralens. In cases of psoriasis and vitiligo, UV light with wavelength of 3. Harmful effects. An overexposure to UVB radiation can cause sunburn and some forms of skin cancer. In humans, prolonged exposure to solar UV radiation may result in acute and chronic health effects on the skin, eye, and immune system. However the most deadly form - malignant melanoma - is mostly caused by the indirect DNA damage (free radicals and oxidative stress). This can be seen from the absence of a UV- signature mutation in 9. UVC rays are the highest energy, most dangerous type of ultraviolet light. Little attention has been given to UVC rays in the past since they are filtered out by the atmosphere. However, their use in equipment such as pond sterilization units may pose an exposure risk, if the lamp is switched on outside of its enclosed pond sterilization unit. Ultraviolet photons harm the DNA molecules of living organisms in different ways. In one common damage event, adjacent Thymine bases bond with each other, instead of across the . This makes a bulge, and the distorted DNA molecule does not function properly. Skin“Ultraviolet (UV) irradiation present in sunlight is an environmental human carcinogen. The toxic effects of UV from natural sunlight and therapeutic artificial lamps are a major concern for human health. The major acute effects of UV irradiation on normal human skin comprise sunburn inflammation erythema, tanning, and local or systemic immunosuppression.” — Matsumura and Ananthaswamy , (2. UVA, UVB and UVC can all damage collagen fibers and thereby accelerate aging of the skin. Both UVA and UVB destroy vitamin A in skin which may cause further damage. In the past UVA was considered less harmful, but today it is known, that it can contribute to skin cancer via the indirect DNA damage (free radicals and reactive oxygen species). It penetrates deeply but it does not cause sunburn. UVA does not damage DNA directly like UVB and UVC, but it can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which in turn can damage DNA. Because it does not cause reddening of the skin (erythema) it cannot be measured in the SPF testing. There is no good clinical measurement of the blocking of UVA radiation, but it is important that sunscreen block both UVA and UVB. Some scientists blame the absence of UVA filters in sunscreens for the higher melanoma- risk that was found for sunscreen users. UVB light can cause direct DNA damage. The radiation excites DNA molecules in skin cells, causing aberrant covalent bonds to form between adjacent cytosine bases, producing a dimer. When DNA polymerase comes along to replicate this strand of DNA, it reads the dimer as . This causes the DNA replication mechanism to add a . This is a mutation, which can result in cancerous growths and is known as a . The mutations that are caused by the direct DNA damage carry a UV signature mutation that is commonly seen in skin cancers. The mutagenicity of UV radiation can be easily observed in bacteria cultures. This cancer connection is one reason for concern about ozone depletion and the ozone hole. UVB causes some damage to collagen but at a very much slower rate than UVA. As a defense against UV radiation, the amount of the brown pigment melanin in the skin increases when exposed to moderate (depending on skin type) levels of radiation; this is commonly known as a sun tan. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, blocking the UV from damaging skin tissue. UVA gives a quick tan that lasts for days by oxidizing melanin that was already present and triggers the release of the melanin from melanocytes. UVB yields a tan that takes roughly 2 days to develop because it stimulates the body to produce more melanin. The photochemical properties of melanin make it an excellent photoprotectant. Ultraviolet - Im Tal des Todes (1.
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