18.10.2014
Although ultraviolet radiation is invisible to the human eye, most people are aware of the effects of UV through sunburn,and in tanning beds. UV light is found in sunlight and is emitted by electric arcs and specialized lights such as black lights. The discovery of UV radiation was associated with the observation that silver salts darken when exposed to sunlight. The name means "beyond violet" (from Latin ultra, "beyond"), violet being the color of the shortest wavelengths of visible light.
In photolithography and laser technology, the term deep ultraviolet or DUV refers to wavelengths below 300 nm. Ordinary glass is partially transparent to UVA but is opaque to shorter wavelengths, whereas silica or quartz glass, depending on quality, can be transparent even to vacuum UV wavelengths. Vacuum UV, which begins at 200 nm, can of course propagate through a vacuum—hence the name—but air is opaque to it, as these wavelengths are strongly absorbed by molecular oxygen in the air.
A black light, Wood's light, or UV light is a lamp that emits long-wave UV radiation and very little visible light. While "black lights" do produce light in the UV range, their spectrum is confined to the long-wave UVA region. A black light may also be formed, very inefficiently, by simply using Wood's glass instead of clear glass as the envelope for a common incandescent bulb. Some UV fluorescent bulbs specifically designed to attract insects use the same near-UV emitting phosphor as normal blacklights, but use plain glass instead of the more expensive Wood's glass. Such low-pressure mercury lamps are used extensively for disinfection, and in standard form have an optimum operating temperature of about 30 degrees Celsius.
Light-emitting diodes (LEDs) can be manufactured to emit light in the ultraviolet range, although practical LED arrays are very limited below 365 nm. UV laser diodes and UV solid-state lasers can be manufactured to emit light in the ultraviolet range.
Ultraviolet detection and measurement technology can vary with the part of the spectrum under consideration.
Technology for VUV instrumentation has been largely driven by solar physics for many decades and more recently some photolithography applications for semiconductors. The health effects ultraviolet radiation has on human health has implications on weighting the risks and benefits of sun exposure, but is also implicated in issues such as fluorescent lamps and health. UVB exposure induces the production of vitamin D in the skin at a rate of up to 1,000 IUs per minute.
Ultraviolet radiation has other medical applications, in the treatment of skin conditions such as psoriasis and vitiligo. On April 13, 2011 the International Agency for Research on Cancer of the World Health Organization classified all categories and wavelengths of Ultraviolet Radiation as a Group 1 carcinogen.
UVA, UVB, and UVC can all damage collagen fibers and, therefore, accelerate aging of the skin. The reddening of the skin due to the action of sunlight depends both on the amount of sunlight and on the sensitivity of the skin ("erythemal action spectrum") over the UV spectrum.
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. Sunscreen prevents the direct DNA damage that causes sunburn by blockage of UVB.[clarification needed] As such, most of these products contain an SPF rating that indicates how well they block UVB as a measure of their effectiveness. Image of a man's face with sunscreen on the left , in visible (left) and UV light, demonstrating how sunscreen protects against UV exposure. Medical organizations recommend patients protect themselves from UV radiation by using sunscreen. However, some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells.[23][24][25] The amount of sunscreen that penetrates through the stratum corneum may or may not be large enough to cause damage. Such effects can be avoided by using newer generations of filter substances or combinations that maintain their UV protective properties even after several hours of solar exposure.
High intensities of UVB light are hazardous to the eyes, and exposure can cause welder's flash (photokeratitis or arc eye) and may lead to cataracts, pterygium,[28][29] and pinguecula formation. UV light is absorbed by molecules known as chromophores, which are present in the eye cells and tissues. Protective eyewear is beneficial to those who are working with or those who might be exposed to ultraviolet radiation, particularly short wave UV. Many polymers used in consumer products are degraded by UV light, and need addition of UV absorbers to inhibit attack, especially if the products are exposed to sunlight.
In addition, many pigments and dyes absorb UV and change colour, so paintings and textiles may need extra protection both from sunlight and fluorescent bulbs, two common sources of UV radiation. Ultraviolet Light Absorbers (UVAs) are molecules used in organic materials (polymers, paints, etc.) to absorb UV light to reduce the UV degradation (photo-oxidation) of a material.
UV is an investigative tool at the crime scene helpful in locating and identifying bodily fluids (semen, blood,[citation needed] bile etc.).
Some animals, including birds, reptiles, and insects such as bees, can see near-ultraviolet light. Butterflies use ultraviolet as a communication system for sex recognition and mating behavior. Many insects use the ultraviolet wavelength emissions from celestial objects as references for flight navigation. UV lamps including newer LEDs (light-emitting diode) aid in the detection of organic mineral deposits that remain on surfaces where periodic cleaning and sanitizing may not be properly accomplished. Using a catalytic reaction from titanium dioxide and UV light exposure, a strong oxidative effect occurs on any organic objects that pass through the media, converting otherwise irritating pathogens, pollens, and mold spores into harmless inert byproducts. A collection of mineral samples brilliantly fluorescing at various wavelengths as seen while being irradiated by UV light.
Ultraviolet lamps are also used in analyzing minerals and gems, and in other detective work including authentication of various collectibles. In other detective work including authentication of various collectibles and art, and detecting counterfeit currency absent of marker dyes. UV fluorescent dyes are used in many applications (for example, biochemistry and forensics). Exposure to UVA light while the skin is hyper-photosensitive by taking psoralens is an effective treatment for psoriasis called PUVA. Typical treatment regimes involve short exposure to UVB rays 3 to 5 times a week at a hospital or clinic, and repeated sessions may be required before results are noticeable. Side-effects may include itching and redness of the skin due to UVB exposure, and possibly sunburn, if patients do not minimize exposure to natural UV rays during treatment days.
Certain fungal growths under the toenail can be treated using a specific wavelength of UV delivered from a high-power LED (light-emitting diode) and can be safer than traditional systemic drugs. Ultraviolet radiation is used for very fine resolution photolithography, a procedure wherein a chemical called a photoresist is exposed to UV radiation that has passed through a mask. UV radiation is used extensively in the electronics industry because photolithography is used in the manufacture of semiconductors, integrated circuit components,[41] and printed circuit boards.
An application of UV is to detect corona discharge (often called "corona") on electrical apparatus.
The Allpondpumps UV Light Steriliser has a unique design which feeds the water through a special helix, meaning the water does not just run through the UV but spins inside, allowing the UV more exposure before the water exits the outlet.
This form of sterilising enables increased efficiency from a more-even exposure of the water to the UV. This model comes with an advanced thermal protection feature, which automatically shuts the unit down if in danger of overheating.
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The Advantage And Disvantage Of Input Devices; Input devices serve a purpose but also come with a few disadvantages. To get started with moderating, editing, and deleting comments, please visit the Comments screen in the dashboard. Audi a8 – wikipedia, the free encyclopedia, The audi a8 is a four-door, full-size, luxury sedan car manufactured and marketed by the german automaker audi since 1994. Audi reveals new beefed-up a8 l security – autoblog, Audi claims is the lightest armored vehicle of its kind. Audi’s a8 l security sedan takes road safety to the next level, From the street, audi’s a8 l security sedan looks like any other no-nonsense vehicle out of germany. Audi rolls out 2015 a8 l security – motor authority, Though it wasn’t on show with the rest of the updated 2015 a8 range at the detroit auto show this week, audi’s 2015 a8 l security has also received a round of. It is named because the spectrum consists of electromagnetic waves with frequencies higher than those that humans identify as the color violet. In 1801, 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 lightening silver chloride-soaked paper.
In the long-wave limit of this region, roughly 150–200 nm, the principal absorber is the oxygen in air. Pure nitrogen (with less than about 10 ppm oxygen) is transparent to wavelengths in the range of about 150–200 nm. Fluorescent black lights are typically made in the same fashion as normal fluorescent lights, except that a different phosphor is used on the inside of the tube which emits UV instead of visible light, and the 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 400 nanometres. Plain glass blocks less of the visible mercury emission spectrum, making them appear light-blue to the naked eye. Use of a mercury amalgam allows operating temperature to rise to 100 degrees Celsius, and UVC emission to about double or triple per unit of light-arc length.
While some silicon detectors are used across the spectrum, and in fact the US NIST has characterized simple silicon diodes[11] that work with visible light too, many specializations are possible for different applications.
While optics can be used to remove unwanted visible light that contaminates the VUV, in general, detectors can be limited by their response to non-VUV radiation, and the development of "solar-blind" devices has been an important area of research. UVA radiation has been much used in conjunction with psoralens (PUVA treatment) for psoriasis, although this treatment is less used now because the combination produces dramatic increases in skin cancer, and because treatment with UVB radiation by itself is more effective. However the most deadly form - malignant melanoma - is mostly caused by the indirect DNA damage (free radicals and oxidative stress). Little attention has been given to UVC rays in the past since they are filtered out by the atmosphere. This is the highest level designation for carcinogens and means "There is enough evidence to conclude that it can cause cancer in humans". In one common damage event, adjacent thymine bases bond with each other, instead of across the "ladder". The toxic effects of UV from natural sunlight and therapeutic artificial lamps are a major concern for human health. Both UVA and UVB destroy vitamin A in skin, which may cause further damage.[19] In the past, UVA was considered less harmful, but today it is known it can contribute to skin cancer via indirect DNA damage (free radicals and reactive oxygen species). The radiation excites DNA molecules in skin cells, causing aberrant covalent bonds to form between adjacent cytosine bases, producing a dimer. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, blocking the UV from damaging skin tissue. This rating, however, offers no data about protection against UVA, exposure to which does not lead to sunburn but is still harmful.[citation needed] In the US, the Food and Drug Administration is considering adding a star rating system to show UVA protection.
The side of the face with sunscreen, is darker, showing that the sunscreen absorbs the UV light. Five sunscreen ingredients have been shown to protect mice against skin tumors (see sunscreen).
Despite the fact that an answer would be a key to improve formulations of sun protection products, many publications carefully avoid addressing this question.
Chromophores absorb light energy from the various wavelengths at different rates - a pattern known as absorption spectrum. Given that light may reach the eye from the sides, full coverage eye protection is usually warranted if there is an increased risk of exposure, as in high altitude mountaineering. Most plastic lenses give more protection than glass lenses, because, as noted above, glass is transparent to UVA and the common acrylic plastic used for lenses is less so. The problem appears as discoloration or fading, cracking, and, sometimes, total product disintegration if cracking has proceeded sufficiently. Sensitive polymers include thermoplastics, such as polypropylene, polyethylene, and poly(methyl methacrylate) as well as speciality fibers like aramids. Old and antique paintings such as watercolour paintings, for example, usually must be placed away from direct sunlight. They are contrasted with physical "blockers" of UV radiation such as titanium dioxide and zinc oxide. A phosphorescent coating on the inside of the tubes absorbs the UV and converts it to visible light.
Unshielded exposure of the skin or eyes to mercury arc lamps that do not have a conversion phosphor is quite dangerous. Other practical UV sources with more continuous emission spectra include xenon arc lamps (commonly used as sunlight simulators), deuterium arc lamps, mercury-xenon arc lamps, metal-halide arc lamps, and tungsten-halogen incandescent lamps. Because the ozone layer blocks many UV frequencies from reaching telescopes on the surface of the Earth, most UV observations are made from space. Many fruits, flowers, and seeds stand out more strongly from the background in ultraviolet wavelengths as compared to human color vision.
A local ultraviolet emissor will normally disrupt the navigation process and will eventually attract the flying insect. They are attracted to the UV light, and are killed using an electric shock, or trapped once they come into contact with the device. UV radiation is often used in visible spectrophotometry to determine the fluorescence of a given sample. Materials may look the same under visible light, but fluoresce to different degrees under ultraviolet light, or may fluoresce differently under short wave ultraviolet versus long wave ultraviolet. Materials may look the same under visible light, but fluoresce to different degrees under ultraviolet light, or may fluoresce differently under short-wave ultraviolet versus long-wave ultraviolet. Due to the potential of psoralens to cause damage to the liver, PUVA may be used only a limited number of times over a patient's lifetime.
Almost all of the conditions that respond to UVB light are chronic problems, so continuous treatment is required to keep those problems in check. The light causes chemical reactions to occur in the photoresist, and, after development (a step that removes either the exposed or the unexposed photoresist), a pattern determined by the mask remains on the sample. Degradation of insulation in electrical apparatus or pollution causes corona, wherein a strong electric field ionizes the air and excites nitrogen molecules, causing the emission of ultraviolet radiation.
It does not take the place of a biological or mechanical filter, but it kills tiny algae that these filters cannot remove. This improved UV system, the Ultra Violet Clarifier, continues to be a key element of a well filtered clear water system. Once the unit has cooled down to normal temperature it will restart and continue to operate.
He called them "oxidizing rays" to emphasize chemical reactivity and to distinguish them from "heat rays" at the other end of the visible spectrum. In fields like analytics and life sciences, the acronym "XUV" is used for Extreme Ultraviolet for characterizing the broader spectral range, such as to distinguish from EUV. 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.


This has come to have wide practical significance since semiconductor manufacturing processes have been using wavelengths shorter than 200 nm. XUV is strongly absorbed by most known materials, but it is possible to synthesize multilayer optics that reflect up to about 50% of XUV radiation at normal incidence. The color of such lamps is often referred to in the lighting industry as "blacklight blue" or "BLB", to distinguish them from UV lamps used in "bug zapper" insect traps, that do not have the blue Wood's glass. Though cheaper than the fluorescent source, only 0.1% of the input power is converted to usable radiation, as the incandescent light radiates as a black body with very little emission in the UV.
Germicidal lamps use quartz (glass) doped with an additive to block the 185 nm wavelength. These low-pressure lamps have a typical efficiency of approximately thirty to thirty-five percent, meaning that for every 100 watts of electricity consumed by the lamp, it will produce approximately 30-35 watts of total UV output.
Such LED arrays are beginning to be used for UV curing applications, and are already successful in digital print applications and inert UV curing environments.
Ultraviolet lasers have applications in industry (laser engraving), medicine (dermatology and keratectomy), secure communications, and computing (optical storage). Many approaches seek to adapt visible light-sensing technologies, but these can suffer from unwanted response to visible light and various instabilities.
Wide-gap solid-state devices or vacuum devices with high-cutoff photocathodes can be attractive compared to silicon diodes. An appropriate amount of UVB (which varies according to skin color) leads to a limited amount of direct DNA damage.
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. This "thymine dimer" makes a bulge, and the distorted DNA molecule does not function properly. The major acute effects of UV irradiation on normal human skin comprise sunburn inflammation erythema, tanning, and local or systemic immunosuppression. When DNA polymerase comes along to replicate this strand of DNA, it reads the dimer as "AA" and not the original "CC". 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. A similar system is already used in some European countries.[citation needed] Some sunscreen lotions now include compounds such as titanium dioxide, which helps protect against UVA rays. In the first 20 minutes, the film of sunscreen had a protective effect and the amount of ROS was smaller.
If too much UV light is absorbed, eye structures such as the cornea, the lens and the retina can be damaged.
Mountaineers are exposed to higher than ordinary levels of UV radiation, both because there is less atmospheric filtering and because of reflection from snow and ice. UV absorption leads to chain degradation and loss of strength at sensitive points in the chain structure. Common window glass provides some protection by absorbing some of the harmful UV, but valuable artifacts need extra shielding. UVAs can disappear over time, so monitoring of UVA levels in weathered materials is necessary.
Visa stamps and stickers on passports of visitors contain large detailed seals invisible under normal light, but strongly visible under UV illumination.
Scorpions glow or take on a yellow to green color under UV illumination, thus assisting in the control of these arachnids. Different designs of ultraviolet light traps are also used by entomologists for collecting nocturnal insects during faunistic survey studies. Pet urine deposits in carpeting or other hard surfaces can be detected for accurate treatment and removal of mineral tracers and the odor-causing bacteria that feed on proteins within.
The contaminants that pollute the indoor environment are almost entirely based upon organic or carbon-based compounds. Alternatively, air may be treated by passing by a single UV source operating at 184 nm and subsequent catalysis with iron pentaoxide. Many substances, such as proteins, have significant light absorption bands in the ultraviolet that are of use and interest in biochemistry and related fields. The simpler term "chemical rays" was adopted shortly thereafter, and it remained popular throughout the 19th century. XUV is separated from x-rays and VUV, by the fact that the photoelectron ionization of innershell electrons is the - by orders of magnitudes - dominating photon-matter interaction effect. By working in oxygen-free gas, the equipment does not have to be built to withstand the pressure differences required to work in a vacuum.
Incandescent bulbs used to generate significant UV, due to their inefficiency, may become dangerously hot. With the addition of a suitable phosphor (phosphorescent coating) , they can be modified to produce a UVA, UVB, or visible light spectrum (all fluorescent tubes used for domestic and commercial lighting are mercury (Hg) UV emission bulbs at heart). A variety of solid-state and vacuum devices have been explored for use in different parts of the UV spectrum. This is recognized and repaired by the body, then melanin production is increased, which leads to a long-lasting tan.
UVB yields a tan that takes roughly 2 days to develop because it stimulates the body to produce more melanin.[citation needed] The photochemical properties of melanin make it an excellent photoprotectant.
There are protective treatments available for eyeglass lenses that need it, which will give better protection.
Many museums place black curtains over watercolour paintings and ancient textiles, for example.
Many birds have patterns in their plumage that are invisible at usual wavelengths but observable in ultraviolet, and the urine and other secretions of some animals, including dogs, cats, and human beings, is much easier to spot with ultraviolet.
Many hospitality industries use UV lamps to inspect for unsanitary bedding to determine lifecycle for mattress restoration as well as general performance of the cleaning staff. This is in contrast to x-rays, where scatter is relevant and VUV where the interaction is mainly with outer ("chemical active") electrons of the atoms and molecules. Some other scientific instruments which operate in this spectral region, such as circular dichroism spectrometers, are also commonly nitrogen-purged. More rarely still, high-power (hundreds of watts) mercury-vapor black lights that use a UV-emitting phosphor and an envelope of Wood's glass are made, are used mainly for theatrical and concert displays.
Ultraviolet light can be detected by suitable photodiodes and photocathodes, which can be tailored to be sensitive to different parts of the UV spectrum. But even a treatment that completely blocks UV will not protect the eye from light that arrives around the lens.
Aramid rope must be shielded with a sheath of thermoplastic if it is to retain its strength.The impact of UV on polymers is used in nanotechnology, transplantology, X-ray lithography and other fields for modification of properties (roughness, hydrophobicity) of polymer surfaces.
Since watercolours can have very low pigment levels, they need extra protection from UV light.
Currencies of various countries' banknotes have an image, as well as many multicolored fibers, that are visible only under ultraviolet light. Urine trails of rodents can be detected by pest control technicians for proper treatment of infested dwellings. A perennial news feature for many television news organizations involves an investigative reporter's using a similar device to reveal unsanitary conditions in hotels, public toilets, hand rails, and such. Short-wave ultraviolet light can destroy DNA in living microorganisms and break down organic material found in indoor air.
The mutations caused by the direct DNA damage carry a UV signature mutation that is commonly seen in skin cancers.



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