image of the Sun's corona as seen in deep ultraviolet by the Extreme ultraviolet Imaging Telescope]] Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3eV 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.
Although ultraviolet is invisible to the human eye, most people are aware of the effects of UV through the painful condition of sunburn, but the UV spectrum has many other effects, both beneficial and damaging, to human health.
UV light is found in sunlight and is emitted by electric arcs and specialized lights such as black lights. Most ultraviolet can be classified as non-ionizing radiation, and can cause chemical reactions, and many substances to glow or fluoresce under it. However, the higher energies of the ultraviolet spectrum from about 150 nm ('vacuum' band) are ionizing, but this type of ultraviolet is not very penetrating and is blocked by air.
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.
{|class="wikitable" border="1" |- !Name !Abbreviation !Wavelength range in nanometers !Energy per photon |- |Ultraviolet A, long wave, or black light |UVA |400 nm–315 nm |3.10–3.94 eV |- |Near |NUV |400 nm–300 nm |3.10–4.13 eV |- |Ultraviolet B or medium wave |UVB |315 nm–280 nm |3.94–4.43 eV |- |Middle |MUV |300 nm–200 nm |4.13–6.20 eV |- |Ultraviolet C, short wave, or germicidal |UVC |280 nm–100 nm |4.43–12.4 eV |- |Far |FUV |200 nm–122 nm |6.20–10.2 eV |- |Vacuum |VUV |200 nm–100 nm |6.20–12.4 eV |- |Low |LUV |100 nm–88 nm |12.4–14.1 eV |- |Super |SUV |150 nm–10 nm |8.28–124 eV |- |Extreme |EUV |121 nm–10 nm |10.2–124 eV |}
In photolithography and laser technology, the term deep ultraviolet or DUV refers to wavelengths below 300 nm. Extreme Ultraviolet stands here for discrete spectral ranges of around 13.5 nm (in future planned also 6.x nm) of about 2 % bandwidth. 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. 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. 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.
"Vacuum UV" is so named because it is absorbed strongly by air and is, therefore, used in a vacuum. In the long-wave limit of this region, roughly 150–200 nm, the principal absorber is the oxygen in air. 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.
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. Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm.
The onset of vacuum UV, 200 nm, is defined by the fact that ordinary air is opaque at shorter wavelengths. This opacity is due to the strong absorption of light of these wavelengths by oxygen in the air. Pure nitrogen (less than about 10 ppm oxygen) is transparent to wavelengths in the range of about 150–200 nm. This has wide practical significance now that semiconductor manufacturing processes are using wavelengths shorter than 200 nm. 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. Some other scientific instruments, such as circular dichroism spectrometers, are also commonly nitrogen-purged and operate in this spectral region.
Extreme UV is characterized by a transition in the physics of interaction with matter: Wavelengths longer than about 30 nm interact mainly with the chemical valence electrons of matter, whereas wavelengths shorter than that interact mainly with inner shell electrons and nuclei. The long end of the EUV/XUV spectrum is set by a prominent He+ spectral line at 30.4 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. This technology has been used to make telescopes for solar imaging; it was pioneered by the NIXT and MSSTA sounding rockets in the 1990s; (current examples are SOHO/EIT and TRACE) and for nanolithography (printing of traces and devices on microchips).
While "black lights" do produce light in the UV range, their spectrum is confined to the longwave UVA region. 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 vitamins A and D 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 (less than 0.1% of the input power), 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 that use a UV-emitting phosphor and an envelope of Wood's glass can be found. 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 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 "blacklight" or "BL" in most lighting catalogs.
Ultraviolet light can also be generated by some light-emitting diodes.
Such low-pressure mercury lamps are used extensively for disinfection, and in standard form have an optimum operating temperature of about 30 degrees Celsius. 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. 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.
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.
molecules of living organisms in different ways. In one common damage event, adjacent thymine bases bond with each other, instead of across the "ladder". This "thymine dimer" makes a bulge, and the distorted DNA molecule does not function properly.]]
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 "AA" and not the original "CC". This causes the DNA replication mechanism to add a "TT" on the growing strand. This mutation can result in cancerous growths, and is known as a "classical C-T mutation". The mutations 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 bacterial 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. Older and more widespread sunscreen chemicals cannot dissipate the energy of the excited state as efficiently as melanin, and, therefore, the penetration of these sunscreen ingredients into the lower layers of the skin may increase the amount of free radicals and reactive oxygen species (ROS). In recent years, improved filtering substances have come into use in commercial sunscreen lotions that do not significantly degrade or lose their capacity to protect the skin as the exposure time increases (photostable substances).
Sunscreen prevents the direct DNA damage that causes sunburn. Most of these products contain an SPF rating to show how well they block UVB rays. The SPF rating, however, offers no data about UVA protection. In the US, the Food and Drug Administration is considering adding a star rating system to show UVA protection. A similar system is already used in some European countries. Some sunscreen lotions now include compounds such as titanium dioxide, which helps protect against UVA rays. Other UVA blocking compounds found in sunscreen include zinc oxide and avobenzone.
Medical organizations recommend patients protect themselves from UV radiation by using sunscreen. Five sunscreen ingredients have been shown to protect mice against skin tumors (see sunscreen).
However, some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells. The amount of sunscreen that penetrates through the stratum corneum may or may not be large enough to cause damage. In one study of sunscreens, the authors write:
The question whether UV filters acts on or in the skin has so far not been fully answered. Despite the fact that an answer would be a key to improve formulations of sun protection products, many publications carefully avoid addressing this question.
In an experiment by Hanson et al. published in 2006, the amount of harmful reactive oxygen species (ROS) was measured in untreated and in sunscreen treated skin. In the first 20 minutes, the film of sunscreen had a protective effect and the amount of ROS was smaller. After 60 minutes, however, the amount of absorbed sunscreen was so high, the amount of ROS was higher in the sunscreen treated skin than in the untreated skin. and pinguecula formation.
UV light is absorbed by molecules known as chromophores, which are present in the eye cells and tissues. Chromophores absorb light energy from the various wavelengths at different rates - a pattern known as absorption spectrum. If too much UV light is absorbed, eye structures such as the cornea, the lens and the retina can be damaged.
Protective eyewear is beneficial to those who are working with or those who might be exposed to ultraviolet radiation, particularly short wave UV. 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. 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.
Ordinary, untreated eyeglasses give some protection. 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. Some plastic lens materials, such as polycarbonate, inherently block most UV. There are protective treatments available for eyeglass lenses that need it, which will give better protection. But even a treatment that completely blocks UV will not protect the eye from light that arrives around the lens.
It is known as UV degradation, and is one form of polymer degradation. Sensitive polymers include thermoplastics, such as polypropylene, polyethylene, and poly(methyl methacrylate) as well as speciality fibers like aramids. UV absorption leads to chain degradation and loss of strength at sensitive points in the chain structure. They include tertiary carbon atoms, which in polypropylene occur in every repeat unit. 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 others fields for modification of properties (roughness, hydrophobicity) of polymer surface. For example, it is known about smoothing effect of vacuum ultraviolet (VUV) on a poly(methyl methacrylate) surface.
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. Old and antique paintings such as watercolour paintings, for example, usually must be placed away from direct sunlight. Common window glass provides some protection by absorbing some of the harmful UV, but valuable artifacts need extra shielding. Many museums place black curtains over watercolour paintings and ancient textiles, for example. Since watercolours can have very low pigment levels, they need extra protection from UV light.
In sunscreen, ingredients that absorb UVA/UVB rays, such as avobenzone and octyl methoxycinnamate, are known as absorbers. They are contrasted with physical "blockers" of UV radiation such as titanium dioxide and zinc oxide. (See sunscreen for a more complete list.)
Some brands of pepper spray will leave an invisible chemical (UV dye) that is not easily washed off on a pepper sprayed attacker, which would help police identify them later.
The main mercury emission wavelength is in the UVC range. Unshielded exposure of the skin or eyes to mercury arc lamps that do not have a conversion phosphor is quite dangerous.
The light from a mercury lamp is predominantly at discrete wavelengths. 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.
In astronomy, very hot objects preferentially emit UV radiation (see Wien's law). Because the ozone layer blocks many UV frequencies from reaching telescopes on the surface of the Earth, most UV observations are made from space. (See UV astronomy, space observatory.)
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. A local ultraviolet emissor will normally disrupt the navigation process and will eventually attract the flying insect. in the Paraguayan Chaco.]] Ultraviolet traps called bug zappers are used to eliminate various small flying insects. They are attracted to the UV light, and are killed using an electric shock, or trapped once they come into contact with the device. Different designs of ultraviolet light traps are also used by entomologists for collecting nocturnal insects during faunistic survey studies.
UV light has also been shown (by KJ Scott et al) as effective in reducing gaseous contaminants such as carbon monoxide and VOCs. Scott and his colleagues demonstrated that the correct mixture of UV lamps radiating at 184 and 254nm can remove LOW concentrations hydrocarbons and carbon monoxide, if the lamps are held in a radiation chamber (a box or drum) and the air is recycled between the room and the reaction chamber. This arrangement prevents the introduction of ozone into the treated air. Alternatively, air may be treated by passing by a=a single UV source operating at 184nm and subsequent catalysis with iron oxide. The iron oxides remove the ozone produced by the UV lamp.
Ultraviolet lamps are also used in analyzing minerals and gems, and in other detective work including authentication of various collectibles. 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.
Exposure to UVB light, in particular, the 310 nm narrowband UVB range, is an effective long-term treatment for many skin conditions like psoriasis, vitiligo, eczema, and others. UVB phototherapy does not require additional medications or topical preparations for the therapeutic benefit; only the light exposure is needed. However, phototherapy can be effective when used in conjunction with certain topical treatments such as anthralin, coal tar, and Vitamin A and D derivatives, or systemic treatments such as methotrexate and soriatane.
Typical treatment regimes involve short exposure to UVB rays 3 to 5 times a week at a hospital or clinic, and up to 30 or more sessions may be required before results are noticeable. Almost all of the conditions that respond to UVB light are chronic problems, so continuous treatment is required to keep those problems in check. Home UVB systems are common solutions for those whose conditions respond to treatment. Home systems permit patients to treat themselves every other day (the ideal treatment regimen for most) without the frequent, costly trips to the office/clinic and back.
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. Cataracts can frequently develop if the eyes are not protected from UVB light exposure. There is no link between an increase in the patient's risk for skin cancer and the proper use of UVB phototherapy. "Proper use" is generally defined as reaching the "Sub-Erythemic Dose" (S.E.D.), the maximum amount of UVB your skin can receive without burning.
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.
UV radiation is used extensively in the electronics industry because photolithography is used in the manufacture of semiconductors, integrated circuit components, and printed circuit boards.
with shortwave UV light when not in use, sterilizing microbiological contaminants from irradiated surfaces.]]
Ultraviolet lamps are used to sterilize workspaces and tools used in biology laboratories and medical facilities. Commercially available low-pressure mercury-vapor lamps emit about 86% of their light at 254 nanometers (nm), which coincides very well with one of the two peaks of the germicidal effectiveness curve (i.e., effectiveness for UV absorption by DNA). One of these peaks is at about 265 nm and the other is at about 185 nm. Although 185 nm is better absorbed by DNA, the quartz glass used in commercially available lamps, as well as environmental media such as water, are more opaque to 185 nm than 254 nm (C. von Sonntag et al., 1992). UV light at these germicidal wavelengths causes adjacent thymine molecules on DNA to dimerize; if enough of these defects accumulate on a microorganism's DNA, its replication is inhibited, thereby rendering it harmless (even though the organism may not be killed outright). However, since microorganisms can be shielded from ultraviolet light in small cracks and other shaded areas, these lamps are used only as a supplement to other sterilization techniques.
New York City has approved the construction of a 2-billion-US-gallon-per-day (7,600,000 m3/d) ultraviolet drinking water disinfection facility. There are also several facilities under construction and several in operation that treat waste water with several stages of filters, hydrogen peroxide, and UV light to bring the water up to drinking standards. One such facility exists in Orange County, California. NASA has examined the use of this technology, using titanium dioxide as catalyst, for breaking down harmful products in spacecraft waste water.
It used to be thought that UV disinfection was more effective for bacteria and viruses, which have more exposed genetic material, than for larger pathogens that have outer coatings or that form cyst states (e.g., Giardia) that shield their DNA from the UV light. However, it was recently discovered that ultraviolet radiation can be somewhat effective for treating the microorganism Cryptosporidium. The findings resulted in the use of UV radiation as a viable method to treat drinking water. Giardia in turn has been shown to be very susceptible to UV-C when the tests were based on infectivity rather than excystation. It has been found that protists are able to survive high UV-C doses but are sterilized at low doses.
Solar water disinfection (SODIS) has been extensively researched in Switzerland and has proven ideal to treat small quantities of water cheaply using natural sunlight. Contaminated water is poured into transparent plastic bottles and exposed to full sunlight for six hours. The sunlight treats the contaminated water through two synergetic mechanisms: UV-A irradiation and increased water temperature. If the water temperatures rises above , the disinfection process is three times faster.
UV detectors are sensitive to most fires, including hydrocarbons, metals, sulfur, hydrogen, hydrazine, and ammonia. Arc welding, electrical arcs, lightning, X-rays used in nondestructive metal testing equipment (though this is highly unlikely), and radioactive materials can produce levels that will activate a UV detection system. The presence of UV-absorbing gases and vapors will attenuate the UV radiation from a fire, adversely affecting the ability of the detector to detect flames. Likewise, the presence of an oil mist in the air or an oil film on the detector window will have the same effect.
An industry has developed around the manufacture of UV sources for UV curing applications. This includes UV lamps, UV LEDs, and Excimer Flash lamps. Fast processes such as flexo or offset printing require high-intensity light focused via reflectors onto a moving substrate and medium; and high-pressure Hg (mercury) or Fe (iron, doped)-based bulbs are used, which can be energized with electric arc or microwaves. Lower-power sources (fluorescent lamps, LED) can be used for static applications, and, in some cases, small high-pressure lamps can have light focused and transmitted to the work area via liquid-filled or fiber-optic light guides.
Japan's National Institute of Advanced Industrial Science and Technology (AIST) has succeeded in developing a transparent solar cell that uses ultraviolet light to generate electricity but allows visible light to pass through it. Most conventional solar cells use visible and infrared light to generate electricity. In contrast, the innovative new solar cell uses ultraviolet radiation. Used to replace conventional window glass, the installation surface area could be large, leading to potential uses that take advantage of the combined functions of power generation, lighting and temperature control.
Also PEDOT-PSS solar cells is an ultraviolet (UV) light-selective and -sensitive photovoltaic cell easily fabricated.
On the other hand, a nanocrystalline layer of Cu2O in the construction of photovoltaic cells increases their ability to utilize UV radiations for photocurrent generation.
UV light of a specified spectrum and intensity is used to stimulate fluorescent dyes so as to highlight defects in a broad range of materials. These dyes may be carried into surface-breaking defects by capillary action (liquid penetrant inspection) or they may be bound to ferrite particles caught in magnetic leakage fields in ferrous materials (magnetic particle inspection).
Category:Electromagnetic spectrum Category:Printing Category:Light therapy
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