False-color image of the solar corona as seen in deep ultraviolet light at 17. A false-color image is an image that depicts a subject in Colors that differ from those a faithful full-color photograph would show The Sun (Sol is the Star at the center of the Solar System. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily 1 nm by the Extreme ultraviolet Imaging Telescope instrument aboard the SOHO spacecraft

An ultraviolet photograph of the Earth taken from the Moon by Apollo 16 astronauts. A nanometre ( American spelling: nanometer, symbol nm) ( Greek: νάνος nanos dwarf; μετρώ metrό count) is a The Extreme ultraviolet Imaging Telescope ( EIT) is an instrument on the SOHO Spacecraft used to obtain high-resolution The Solar and Heliospheric Observatory ( SOHO) is a Spacecraft that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December

Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. X-radiation (composed of X-rays) is a form of Electromagnetic radiation. It is so named because the spectrum consists of electromagnetic waves with frequencies higher than those that humans identify as the color violet. As the name of a color violet (named after the flower violet) is used in two senses first referring to the color of Light at the short- Wavelength

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. A sunburn is a burn to living tissue such as Skin produced by overexposure to Ultraviolet (UV radiation commonly from the Sun 's rays 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 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 darkening silver chloride-soaked paper. Johann Wilhelm Ritter ( December 16, 1776 – January 23, 1810) was a German Chemist and Physicist. Silver chloride is a Chemical compound with the Chemical formula Ag[[Chlorine Cl]] He called them "de-oxidizing rays" to emphasize their chemical reactivity and to distinguish them from "heat rays" at the other end of the visible spectrum. The simpler term "chemical rays" was adopted shortly thereafter, and it remained popular throughout the 19th century. The terms chemical and heat rays were eventually dropped in favor of ultraviolet and infrared radiation, respectively. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Radiation, as in Physics, is Energy in the form of waves or moving Subatomic particles emitted by an atom or other body as it changes from a higher energy ^[1]

Origin of term

The name means "beyond violet" (from Latin ultra, "beyond"), violet being the color of the shortest wavelengths of visible light. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. As the name of a color violet (named after the flower violet) is used in two senses first referring to the color of Light at the short- Wavelength 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-21348)^[2] describes the following ranges:

In photolithography, in laser technology, etc. Photolithography (also called optical lithography) is a process used in Microfabrication to selectively remove parts of a thin film (or the bulk of a substrate A laser is a device that emits Light ( Electromagnetic radiation) through a process called Stimulated emission. , the term deep ultraviolet or DUV refers to wavelengths below 300 nm. "Vacuum UV" is so named because it is absorbed strongly by air and is therefore used in a vacuum. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five In the long-wave limit of this region, roughly 150–200 nm, the principal absorber is the oxygen in air. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the 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

Main article: Black light

A black light, or Wood's light, is a lamp that emits long wave UV radiation and very little visible light. A Black light or UV Light is a lamp emitting Electromagnetic radiation that is almost exclusively in the soft near ultraviolet range and emits Commonly these are referred to as simply a "UV light". 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 400 nanometers. Wood's glass was developed by Robert Williams Wood (1868&ndash1955 as a light filter used in communications during World War I. The color of such lamps is often referred to in the trade as "blacklight blue" or "BLB. " This is to distinguish these lamps from "bug zapper" blacklight ("BL") lamps that don't have the blue Wood's glass. The phosphor typically used for a near 368 to 371 nanometer emission peak is either europium-doped strontium fluoroborate (SrB4O7F:Eu2+) or europium-doped strontium borate (SrB4O7:Eu2+) while the phosphor used to produce a peak around 350 to 353 nanometers is lead-doped barium silicate (BaSi2O5:Pb+). "Blacklight Blue" lamps peak at 365 nm.

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 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. In Physics, a black body is an object that absorbs all light that falls on it 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 "blacklight" or "BL" in most lighting catalogs.

Ultraviolet light can also be generated by some light-emitting diodes.

Natural sources of UV

The Sun emits ultraviolet radiation in the UVA, UVB, and UVC bands, but because of absorption in the atmosphere's ozone layer, 98. The Sun (Sol is the Star at the center of the Solar System. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five The photochemical mechanisms that give rise to the ozone layer were worked out by the British physicist Sidney Chapman in 1930 7% of the ultraviolet radiation that reaches the Earth's surface is UVA. (Some of the UVB and UVC radiation is responsible for the generation of the ozone layer. )

Ordinary glass is partially transparent to UVA but is opaque to shorter wavelengths while Silica or quartz glass, depending on quality, can be transparent even to vacuum UV wavelengths. Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many Fused quartz and fused silica are types of Glass containing primarily Silica in amorphous (non- Crystalline form Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm. ^[3][4][5]

The onset of vacuum UV, 200 nm, is defined by the fact that ordinary air is opaque below this wavelength. 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. Circular dichroism (CD is a form of Spectroscopy based on the differential absorption of left- and right-handed circularly polarized Light.

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, while wavelengths shorter than that interact mainly with inner shell electrons and nuclei. In chemistry valence electrons are the Electrons contained in the outermost or valence, Electron shell of an Atom. The long end of the EUV/XUV spectrum is set by a prominent He⁺ spectral line at 30. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range compared 4nm. 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. An optical coating is a thin layer of material deposited on an optical component such as a lens or Mirror, which alters the way in which the optic Angle of incidence is a measure of deviation of something from "straight on" for example in the approach of a ray to a surface or the angle 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). The Sun (Sol is the Star at the center of the Solar System. The Multi-spectral solar telescope array, or MSSTA, was a Sounding rocket payload built by Professor A The Solar and Heliospheric Observatory ( SOHO) is a Spacecraft that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December TRACE ( Transition Region and Coronal Explorer) is a NASA space telescope designed to investigate the connections between fine-scale magnetic fields and Nanolithography — or Photolithography at the Nanometer scale — refers to the fabrication of nanometer-scale structures, meaning patterns with at Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside

Human health-related effects of UV radiation

Beneficial effects

The Earth's atmosphere blocks UV radiation from penetrating through the atmosphere by 98. 7%. A positive effect of UVB exposure is that it induces the production of vitamin D in the skin. Vitamin D is a group of fat-soluble Prohormones, the two major forms of which are vitamin D2 (or Ergocalciferol) and vitamin D3 (or 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. ^[6] 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. Osteomalacia is the general term for the softening of the bones due to defective Bone mineralization. Other studies show most people get adequate Vitamin D through food and incidental exposure. ^[7]

Many countries have fortified certain foods with Vitamin D to prevent deficiency. Fortifications are Military Constructions and Buildings designed for defense in Warfare Humans have constructed defensive works for 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. ^[7]

Too little UVB radiation leads to a lack of Vitamin D. Too much UVB radiation leads to direct DNA damages and sunburn. Direct DNA damage can occur when DNA directly absorbs the UV-B-photon An appropriate amount of UVB (What is appropriate depends on your skin colour) leads to a limited amount of direct DNA damage. Direct DNA damage can occur when DNA directly absorbs the UV-B-photon 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. Psoriasis (səˈraɪəsɪs ( suh-RI-uh-sus) is a non-contagious disorder which affects the Skin and Joints It commonly causes red scaly Vitiligo (ˈvɪtəˈlaɪgoʊ or leukoderma is a chronic skin disease that causes loss of pigment, resulting in irregular pale patches of Skin UVA radiation can be used in conjunction with psoralens (PUVA treatment). PUVA is a Psoralen + UVA treatment for Eczema, Psoriasis and Vitiligo, and Mycosis fungoides[http //www UVB radiation is rarely used in conjunction with psoralens. Psoralen (also called psoralene) is the parent compound in a family of natural products known as Furocoumarins ' In cases of psoriasis and vitiligo, UV light with wavelength of 311 nm is most effective. Psoriasis (səˈraɪəsɪs ( suh-RI-uh-sus) is a non-contagious disorder which affects the Skin and Joints It commonly causes red scaly Vitiligo (ˈvɪtəˈlaɪgoʊ or leukoderma is a chronic skin disease that causes loss of pigment, resulting in irregular pale patches of Skin

Harmful effects

An overexposure to UVB radiation can cause sunburn and some forms of skin cancer. A sunburn is a burn to living tissue such as Skin produced by overexposure to Ultraviolet (UV radiation commonly from the Sun 's rays In humans, prolonged exposure to solar UV radiation may result in acute and chronic health effects on the skin, eye, and immune system. Health effects, health impacts or health risks are changes in Health resulting from exposure to a source The skin is the outer covering of living tissue of an animal (or plant An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor ^[8] However the most deadly form - malignant melanoma - is mostly caused by the indirect DNA damage (free radicals and oxidative stress). Indirect DNA damage occurs when a UV-photon is absorbed in the human skin by a Chromophore that does not have the ability to convert the energy into This can be seen from the absence of a UV-signature mutation in 92% of all melanoma. ^[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. Sterilization (or sterilisation, see spelling differences) refers to any process that effectively kills or eliminates transmissible agents (such as Fungi

Ultraviolet photons harm the DNA molecules of living organisms in different ways. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known In one common damage event, adjacent Thymine bases bond with each other, instead of across the "ladder". Thymine is one of the four bases in the Nucleic acid of DNA that make up the letters ATGC This makes a bulge, and the distorted DNA molecule does not function properly.

Skin

UVA, UVB and UVC can all damage collagen fibers and thereby accelerate aging of the skin. Collagen is the main Protein of Connective tissue in Animals and the most abundant protein in Mammals making up about 50% of the whole-body protein Both UVA and UVB destroy vitamin A in skin which may cause further damage. ^[11] 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). Indirect DNA damage occurs when a UV-photon is absorbed in the human skin by a Chromophore that does not have the ability to convert the energy into It penetrates deeply but it does not cause sunburn. A sunburn is a burn to living tissue such as Skin produced by overexposure to Ultraviolet (UV radiation commonly from the Sun 's rays 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. Sunscreen (also known as sunblock or suntan lotion) is a Lotion, spray or other Topical product that absorbs or reflects the Sun 's There is no good clinical measurement of the blocking of UVA radiation, but it is important that sunscreen block both UVA and UVB. Sunscreen (also known as sunblock or suntan lotion) is a Lotion, spray or other Topical product that absorbs or reflects the Sun 's Some scientists blame the absence of UVA filters in sunscreens for the higher melanoma-risk that was found for sunscreen users. Sunscreen (also known as sunblock or suntan lotion) is a Lotion, spray or other Topical product that absorbs or reflects the Sun 's ^[12]

The reddening of the skin due to the action of sunlight depends both on the amount of sunlight as well as the sensitivity of the skin ("erythemal action spectrum") over the UV spectrum.

UVB light can cause direct DNA damage. Direct DNA damage can occur when DNA directly absorbs the UV-B-photon The radiation excites DNA molecules in skin cells, causing aberrant covalent bonds to form between adjacent cytosine bases, producing a dimer. Excitation is an elevation in energy level above an arbitrary baseline energy state Cytosine is one of the five main bases found in DNA and RNA. It is a Pyrimidine derivative with a Heterocyclic Aromatic ring 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 is a mutation, which can result in cancerous growths and is known as a "classical C-T mutation". In biology mutations are changes to the Nucleotide sequence of the Genetic material of an organism Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled The mutations that are caused by the direct DNA damage carry a UV signature mutation that is commonly seen in skin cancers. Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled The mutagenicity of UV radiation can be easily observed in bacteria cultures. In Biology, a mutagen ( Latin, literally origin of change) is a physical or chemical agent that changes the genetic information (usually DNA) The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have This cancer connection is one reason for concern about ozone depletion and the ozone hole. Ozone depletion describes two distinct but related observations a slow steady decline of about 4 percent per decade in the total amount of Ozone in Earth's UVB causes some damage to collagen but at a very much slower rate than UVA.

As a defense against UV radiation, the body tans when exposed to moderate (depending on skin type) levels of radiation. Human skin color can range from almost black (due to very high concentrations of the dark brown pigment melanin to nearly colorless (appearing reddish white due to the Blood UVA gives a quick tan that last for days by oxidizing melanin that was already present and it triggers the release of the melanin from melanocytes. Melanin is a class of compounds found in the Plant, Animal and Protista kingdoms, where it serves predominantly as a Pigment. UVB yields a tan that takes roughly 2 days to develop because it stimulates the body to produce more melanin. The purpose of melanin is to block UV radiation and to dissipate the energy as harmless heat. Thereby the potential damage to the skin tissues is prevented. The photochemical properties of melanin make it an excellent photoprotectant. The term Photoprotection designates the mechanisms that nature has developed to minimize the damages that the human body suffers when exposed to UV-irradiation However, sunscreen chemicals can not dissipate the energy of the excited state as efficiently as melanin and therefore the penetration of sunscreen ingredients into the lower layers of the skin is increasing the amount of free radicals and ROS. In Chemistry, radicals (often referred to as free radicals) are atoms molecules or ions with Unpaired electrons on an otherwise Open shell ROS is an initialism for any of the following Robotic Operating System Reactive Oxygen Species Raggruppamento Operativo ^[13]

Sunscreen prevents the direct DNA damage which causes sunburn. Sunscreen (also known as sunblock or suntan lotion) is a Lotion, spray or other Topical product that absorbs or reflects the Sun 's Direct DNA damage can occur when DNA directly absorbs the UV-B-photon Most of these products contain an SPF rating to show how well they block UVB rays. Sunscreen (also known as sunblock or suntan lotion) is a Lotion, spray or other Topical product that absorbs or reflects the Sun 's The SPF rating, however, offers no data about UVA protection. In the US, the FDA 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. Titanium dioxide, also known as titanium(IV oxide or titania, is the naturally occurring Oxide of Titanium, chemical formula Ti[[oxygen Other UVA blocking compounds found in sunscreen include zinc oxide and avobenzone. Zinc oxide is a Chemical compound with the formula ZnO It is nearly insoluble in water but soluble in Acids and Bases It occurs Avobenzone ( Trade names Parsol 1789, Eusolex 9020, Escalol 517 and others INCI Butyl Methoxydibenzoylmethane is an oil soluble Cantaloupe extract, rich in the compound superoxide dismutase (SOD), can be bound with gliadin to form glisodin, an orally-effective protectant against UVB radiation. Cantaloupe (also cantaloup) refers to two varieties of Muskmelon ( Cucumis melo), which is a Species in the family Cucurbitaceae (a The enzyme superoxide dismutase ( SOD,) catalyzes the Dismutation of Superoxide into Oxygen and Hydrogen peroxide. Gliadin is a Glycoprotein present in Wheat and several other Cereals within the grass genus Triticum. Glisodin is a Nutritional supplement based on two constituents Cantaloupe extract which typically contains high quantities of the Enzyme There are also naturally occurring compounds found in rainforest plants that have been known to protect the skin from UV radiation damage, such as the fern Phlebodium aureum. Phlebodium aureum ( Golden polypody, Golden serpent fern or Cabbage palm fern; syn

Sunscreen safety debate

Main article: Sunscreen controversy

The majority of doctors recommend patients protect themselves from UV radiation using sunscreen. Sunscreen protects against two common forms of skin cancer Squamous cell carcinoma (SCC and Basal cell carcinoma (BCC and several sunscreen ingredients protect These recommendations exist despite the ample evidence in the scientific literature that the sunscreen chemicals are harmful if they are illuminated while in contact with living cells. ^[14][15][16] It is undisputed in the scientific literature, that sunscreen chemicals in contact with living tissue are harmful. However, the proponents of sunscreen claim that the amount of sunscreen which penetrates through the stratum corneum is not large enough to cause damage. The stratum corneum ("horny layer" is the outermost layer of the epidermis (the outermost layer of the Skin) The Authors Chatelain et al. criticize (page 34)[file]:

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 that was published in 2006 by Hanson et al, the amount of harmful reactive oxygen species (ROS) had been measured in untreated and in sunscreen treated skin. Reactive oxygen species (ROS are ions or very small molecules that include Oxygen Ions free radicals, and Peroxides both inorganic and In the first 20 minutes the film of sunscreen had a protective effect and the number of ROS species was smaller. After 60 minutes however the amount of absorbed sunscreen was so high, that the amount of ROS was higher in the sunscreen treated skin than in the untreated skin. ^[13]

Eye

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,^[17][18] and pinguecula formation. Arc eye, also known as welder's flash, bake eyes, corneal flash burns, or flash burns, is a painful ocular condition sometimes experienced by Arc eye, also known as welder's flash, bake eyes, corneal flash burns, or flash burns, is a painful ocular condition sometimes experienced by Arc eye, also known as welder's flash, bake eyes, corneal flash burns, or flash burns, is a painful ocular condition sometimes experienced by A cataract is a clouding that develops in the crystalline lens of the Eye or in its envelope varying in degree from slight to complete opacity Pterygium refers to any winglike triangular membrane occurring in the Neck, eyes Knees elbows Ankles A pinguecula is a common type of conjunctival degeneration in the Eye.

Protective eyewear is beneficial to those who are working with or those who might be exposed to ultraviolet radiation, particularly short wave UV. Eye protection is Protective clothing for the Eyes which comes in many types depending upon the threat that is to be reduced 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. Glasses, also called eyeglasses or spectacles, are frames bearing lenses worn in front of the Eyes normally for vision correction, 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.

Degradation of polymers, pigments and dyes

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 used externally and so exposed to sunlight. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun. The problem appears as discoloration or fading, cracking and sometimes, total product disintegration if cracking has proceeded far enough. The rate of attack increases with exposure time and sunlight intensity.

It is known as UV degradation, and is one form of polymer degradation. Many natural and synthetic Polymers are attacked by Ultra-violet radiation and products made using these materials may crack or disintegrate Polymer degradation is a change in the properties - Tensile strength, Colour, shape etc - of a Polymer or polymer based product under the influence of Sensitive polymers include thermoplastics, such as polypropylene and polyethylene as well as speciality fibres like aramids. Polypropylene or polypropene ( PP) is a Thermoplastic Polymer, made by the Chemical industry and used in a wide variety of applications Polyethylene or polythene ( IUPAC name poly(ethene) is a Thermoplastic commodity heavily used in consumer products (notably the Aramid fibers are a class of heat-resistant and strong Synthetic fibers They are used in aerospace and military applications for ballistic rated body armor 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. A carbon-carbon bond is a Covalent bond between two Carbon Atoms. Polypropylene or polypropene ( PP) is a Thermoplastic Polymer, made by the Chemical industry and used in a wide variety of applications An essential concept which defines Polymer structure the repeat unit is the simplest structural unit of a Polymer chain.

In addition, many pigments and dyes absorb UV and change colour, so paintings and textiles may need extra protection both from sunlight and fluorescent lamps, two common sources of UV radiation. For the drug referred to as "pigment" see Black tar heroin. A dye can generally be described as a Colored substance that has an affinity to the substrate to which it is being applied Painting (pān'tīng in Art, is the practice of applying Color to a Surface (support base such as e A textile is a flexible material comprised of a network of natural or artificial Fibres often referred to as thread or Yarn. A fluorescent lamp or fluorescent tube is a Gas-discharge lamp that uses Electricity to excite mercury Vapor. Old and antique paintings such as watercolour paintings for example, usually need to be placed away from direct sunlight. An antique ( Latin: antiquus; old is an old Collectible item It is collected or desirable because of its age rarity condition utility or other unique Watercolor ( US) or Watercolour ( UK) (and "aquarelle" in French is a Painting method Common window glass provides some protection by absorbing some of the harmful UV, but valuable artifacts need shielding. Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many

Blockers and absorbers

Ultraviolet Light Absorbers (UVAs) are molecules used in organic materials (polymers, paints, etc. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds Paint is any Liquid, liquifiable or mastic composition which after application to a substrate in a thin layer is converted to an opaque Solid ) to absorb UV light in order to reduce the UV degradation (photo-oxidation) of a material. Many natural and synthetic Polymers are attacked by Ultra-violet radiation and products made using these materials may crack or disintegrate A number of different UVAs exist with different absorption properties. UVAs can disappear over time, so monitoring of UVA levels in weathered materials is necessary.

In sunscreen, ingredients which absorb UVA/UVB rays, such as avobenzone and octyl methoxycinnamate, are known as absorbers. Sunscreen (also known as sunblock or suntan lotion) is a Lotion, spray or other Topical product that absorbs or reflects the Sun 's They are contrasted with physical "blockers" of UV radiation such as titanium dioxide and zinc oxide. Titanium dioxide, also known as titanium(IV oxide or titania, is the naturally occurring Oxide of Titanium, chemical formula Ti[[oxygen Zinc oxide is a Chemical compound with the formula ZnO It is nearly insoluble in water but soluble in Acids and Bases It occurs (See sunscreen for a more complete list. Sunscreen (also known as sunblock or suntan lotion) is a Lotion, spray or other Topical product that absorbs or reflects the Sun 's )

Applications of UV

Security

A bird appears on many Visa credit cards when held under a UV light source.

To help thwart counterfeiters, sensitive documents (e. A counterfeit is an imitation that is made usually with the intent to deceptively represent its content or origins g. credit cards, driver's licenses, passports) may also include a UV watermark that can only be seen when viewed under a UV-emitting light. A credit card is part of a system of Payments named after the small Plastic card issued to users of the system A driver's license, driver license, driver licence, or driving licence is an official document which states that a person may operate a A passport is a document issued by a national government which certifies for the purpose of international travel the identity and nationality of its holder Passports issued by most countries usually contain UV sensitive inks and security threads. Visa stamps and stickers on passports of visitors contain large and detailed seals invisible to the naked eye under normal lights, but strongly visible under UV illumination. A visa (short for the Latin carta visa, lit "a document that has been seen" is a document issued by a Country giving an individual The naked eye is a Figure of speech referring to human Visual perception that is unaided by enhancing equipment such as a Telescope or Passports issued by many nations have UV sensitive watermarks on all pages of the passport. Currencies of various countries' banknotes have an image, as well as many multicolored fibers, that are visible only under ultraviolet light. Canadian banknotes are the Banknotes of Canada, denominated in Canadian dollars (CAD

Fluorescent lamps

Fluorescent lamps produce UV radiation by ionising low-pressure mercury vapour. A fluorescent lamp or fluorescent tube is a Gas-discharge lamp that uses Electricity to excite mercury Vapor. Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum A phosphorescent coating on the inside of the tubes absorbs the UV and converts it to visible light.

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. A xenon flash lamp is an Electric glow discharge lamp designed to produce extremely intense incoherent, full-spectrum white light for very short durations

Astronomy

Aurora at Jupiter's north pole as seen in ultraviolet light by the Hubble Space Telescope.

In astronomy, very hot objects preferentially emit UV radiation (see Wien's law). Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study 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. Ultraviolet astronomy is generally used to refer to observations at Ultraviolet wavelengths between approximately 10 and 320 nanometres A space observatory is any instrument in Outer space which is used for observation of distant planets galaxies and other outer space objects )

Biological surveys and pest control

Some animals, including birds, reptiles, and insects such as bees, can see into the near ultraviolet. Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described Bees are flying Insects closely related to Wasps and Ants Bees are a Monophyletic lineage within the superfamily Apoidea Many fruits, flowers, and seeds stand out more strongly from the background in ultraviolet wavelengths as compared to human color vision. Scorpions glow or take on a yellow to green color under UV illumination. Scorpions are eight-legged Carnivorous Arthropods They are members of the order Scorpiones within the class Arachnida. 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 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 would eventually attract to itself the flying insect.

Entomologist using a UV light for collecting beetles in the Paraguayan Chaco. Beetles are the group of Insects with the largest number of known Species. Paraguay, officially the Republic of Paraguay ( Spanish: República del Paraguay; Guaraní: Tetã Paraguái) is one of the only

Ultraviolet traps 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. Entomology (from Greek grc ἔντομος entomos, "that which is cut in pieces or engraved/segmented" hence "insect" and grc -λογία In Christian Liturgy, a collect kol-ekt' is both a liturgical action and a short general Prayer. As an Animal behavior, nocturnality describes sleeping during the Daytime and being active at Night - the opposite of the diurnal

Spectrophotometry

UV/VIS spectroscopy is widely used as a technique in chemistry, to analyze chemical structure, most notably conjugated systems. Ultraviolet-visible spectroscopy or ultraviolet-visible spectrophotometry ( UV/ VIS) involves the Spectroscopy of Photons in the UV-visible Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Chemical structure refers to Molecular geometry, Electronic structure and Crystal structure. A chemically conjugated system is a system of atoms Covalently bonded with alternating single and multiple (e UV radiation is often used in visible spectrophotometry to determine the existence of fluorescence in a given sample. In Physics, spectrophotometry is the quantitative study of electromagnetic spectra.

Analyzing minerals

A collection of mineral samples brilliantly fluorescing at various wavelengths as seen while being irradiated by UV light. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific

Ultraviolet lamps are also used in analyzing minerals, gems, and in other detective work including authentication of various collectibles. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive Mineral, which &mdash when cut and polished &mdash For the record label see Collectables Records For the Ashanti album see Collectables by Ashanti A collectable 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. Fluorescence is a Luminescence that is mostly found as an

Chemical markers

UV fluorescent dyes are used in many applications (for example, biochemistry and forensics). A dye can generally be described as a Colored substance that has an affinity to the substrate to which it is being applied Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as The Green Fluorescent Protein (GFP) is often used in genetics as a marker. The green fluorescent protein ( GFP) is composed of 238 Amino acids (26 Genetics (from Ancient Greek grc-Latn genetikos, “genitive” and that from grc-Latn genesis, “origin” a discipline of Biology, is Many substances, such as proteins, have significant light absorption bands in the ultraviolet that are of use and interest in biochemistry and related fields. UV-capable spectrophotometers are common in such laboratories.

Photochemotherapy

Exposure to UVA light while the skin is hyper-photosensitive by taking psoralens is an effective treatment for psoriasis called PUVA. Psoralen (also called psoralene) is the parent compound in a family of natural products known as Furocoumarins ' Psoriasis (səˈraɪəsɪs ( suh-RI-uh-sus) is a non-contagious disorder which affects the Skin and Joints It commonly causes red scaly PUVA is a Psoralen + UVA treatment for Eczema, Psoriasis and Vitiligo, and Mycosis fungoides[http //www Due to psoralens potentially causing damage to the liver, PUVA may only be used a limited number of times over a patient's lifetime

Phototherapy

Exposure to UVB light, particularly the 310 nm narrowband UVB range, is an effective long-term treatment for many skin conditions like psoriasis, vitiligo, eczema, and many others. Psoralen (also called psoralene) is the parent compound in a family of natural products known as Furocoumarins ' The liver is a vital organ in the human body and is present in Vertebrates and some other animals PUVA is a Psoralen + UVA treatment for Eczema, Psoriasis and Vitiligo, and Mycosis fungoides[http //www Psoriasis (səˈraɪəsɪs ( suh-RI-uh-sus) is a non-contagious disorder which affects the Skin and Joints It commonly causes red scaly Vitiligo (ˈvɪtəˈlaɪgoʊ or leukoderma is a chronic skin disease that causes loss of pigment, resulting in irregular pale patches of Skin Eczema (from Greek έκζεμα) is a form of Dermatitis, or Inflammation of the Epidermis. 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. ^[19]

Typical treatment regimes involve short exposure to UVB rays 3 to 5 times a week at a hospital or clinic, and for the best results, up to 30 or more sessions may be required.

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.

Photolithography

Ultraviolet radiation is used for very fine resolution photolithography, a procedure where a chemical known as a photoresist is exposed to UV radiation which has passed through a mask. Photolithography (also called optical lithography) is a process used in Microfabrication to selectively remove parts of a thin film (or the bulk of a substrate The light allows chemical reactions to take place in the photoresist, and after development (a step that either removes the exposed or unexposed photoresist), a geometric pattern which is determined by the mask remains on the sample. Further steps may then be taken to "etch" away parts of the sample with no photoresist remaining.

UV radiation is used extensively in the electronics industry because photolithography is used in the manufacture of semiconductors, integrated circuit components^[20] and printed circuit boards. A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside A printed circuit board, or PCB, is used to mechanically support and electrically connect Electronic components using conductive pathways or traces

Checking electrical insulation

A new application of UV is to detect corona discharge (often simply called "corona") on electrical apparatus. In Electricity, a corona discharge is an Electrical discharge brought on by the Ionization of a Fluid surrounding a conductor, which Degradation of insulation of electrical apparatus or pollution causes corona, wherein a strong electric field ionizes the air and excites nitrogen molecules, causing the emission of ultraviolet radiation. The corona degrades the insulation level of the apparatus. Corona produces ozone and to a lesser extent nitrogen oxide which may subsequently react with water in the air to form nitrous acid and nitric acid vapour in the surrounding air. OZONE is an object oriented Operating system written in the C programming language. The term nitrogen oxide typically refers to any Binary compound of Oxygen and Nitrogen, or to a mixture of such compounds Nitric Nitrous acid (molecular formula H[[Nitrogen N]] O 2 is a weak and monobasic Acid known only in Solution and in the form of Nitrite Nitric acid ( H[[nitrate NO3]] also known as Aqua fortis and spirit of nitre, is a highly corrosive and ^[21]

Sterilization

Main article: Ultraviolet germicidal irradiation

A low pressure mercury vapor discharge tube floods the inside of a hood with shortwave UV light when not in use, sterilizing microbiological contaminants from irradiated surfaces. Ultraviolet germicidal irradiation ( UVGI) is a sterilization method that uses Ultraviolet (UV light at sufficiently short Wavelength to break A fume hood or fume cupboard is a large piece of Scientific equipment common to Chemistry laboratories designed to limit a person's exposure to hazardous

Ultraviolet lamps are used to sterilize workspaces and tools used in biology laboratories and medical facilities. Sterilization (or sterilisation, see spelling differences) refers to any process that effectively kills or eliminates transmissible agents (such as Fungi 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. Fused quartz and fused silica are types of Glass containing primarily Silica in amorphous (non- Crystalline form 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). Thymine is one of the four bases in the Nucleic acid of DNA that make up the letters ATGC A dimer is a Chemical or Biological entity consisting of two subunits called Monomers which are held together by either Intramolecular forces 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.

Disinfecting drinking water

UV radiation can be an effective viricide and bactericide. viricide may also refer to the killing of men or husbands see Gendercide. A bactericide or bacteriocide is a substance that kills bacteria and preferably nothing else Disinfection using UV radiation is commonly used in wastewater treatment applications and is finding an increased usage in drinking water treatment. Many bottlers of spring water use UV disinfection equipment to sterilize their water. Solar water disinfection is the process of using PET bottles and sunlight to disinfect water. Solar water disinfection, also known as SODIS is a method of disinfecting water using only Sunlight and plastic PET bottles A pet is an Animal kept for companionship and enjoyment or a househeld animal as opposed to Livestock, Laboratory animals Working animals

New York City has approved the construction of a 2 billion gallon per day ultraviolet drinking water disinfection facility^[22]. 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. ^{[23] [24]}

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 which have outer coatings or that form cyst states (e. g. , Giardia) that shield their DNA from the UV light. Giardia lamblia (synonymous with Lamblia intestinalis and Giardia duodenalis) is a Flagellated Protozoan However, it was recently discovered that ultraviolet radiation can be somewhat effective for treating the microorganism Cryptosporidium. Cryptosporidium is a Protozoan that can cause gastro-intestinal illness with Diarrhea in humans The findings resulted in two US patents and 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. ^[25] It has been found that protists are able to survive high UV-C doses but are sterilized at low doses. Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this

A process named SODIS [1] has been extensively researched in Switzerland and has proven ideal to treat small quantities of water 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: Radiation in the spectrum of UV-A (wavelength 320-400 nm) and increased water temperature. If the water temperatures rises above 50 °C, the disinfection process is three times faster.

Food processing

As consumer demand for fresh and "fresh-like" food products increases, the demand for nonthermal methods of food processing is likewise on the rise. Food processing is the set of methods and techniques used to transform raw Ingredients into Food or to transform food into other forms for consumption by In addition, public awareness regarding the dangers of food poisoning is also raising demand for improved food processing methods. Foodborne illness (also foodborne disease) is any Illness resulting from the consumption of food Ultraviolet radiation is used in several food processes to kill unwanted microorganisms. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually UV light can be used to pasteurize fruit juices by flowing the juice over a high intensity ultraviolet light source. Pasteurization is the process of heating Liquids for the purpose of destroying bacteria, Protozoa, Molds and Yeasts The process was The effectiveness of such a process depends on the UV absorbance of the juice (see Beer's law). In Spectroscopy, the absorbance A is defined as A_\lambda = -\log_{10}(I/I_0\ where I is the intensity of light In

Fire detection

Ultraviolet detectors generally use either a solid-state device, such as one based on silicon carbide or aluminium nitride, or a gas-filled tube as the sensing element. Silicon carbide ( is a compound of Silicon and Carbon bonded together to form Ceramics but it also occurs in nature as the extremely rare mineral Aluminium nitride ( Al[[Nitrogen N]] is a Nitride of Aluminium. UV detectors which are sensitive to UV light in any part of the spectrum respond to irradiation by sunlight and artificial light. Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun. Lighting includes both artificial Light sources such as lamps and natural illumination of interiors from Daylight. A burning hydrogen flame, for instance, radiates strongly in the 185 to 260 nanometer range and only very weakly in the IR region, while a coal fire emits very weakly in the UV band yet very strongly at IR wavelengths; thus a fire detector which operates using both UV and IR detectors is more reliable than one with a UV detector alone. Virtually all fires emit some radiation in the UVB band, while the Sun's radiation at this band is absorbed by the Earth's atmosphere. Thermal radiation is Electromagnetic radiation emitted from the surface of an object which is due to the object's Temperature. The Sun (Sol is the Star at the center of the Solar System. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five The result is that the UV detector is "solar blind", meaning it will not cause an alarm in response to radiation from the Sun, so it can easily be used both indoors and outdoors.

UV detectors are sensitive to most fires, including hydrocarbons, metals, sulfur, hydrogen, hydrazine, and ammonia. In Organic chemistry, a hydrocarbon is an Organic compound consisting entirely of Hydrogen and Carbon. The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Hydrazine is a Chemical compound with the formula N2H4 It has an Ammonia -like odor and is derived from the same industrial chemistry Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor 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. Arc welding uses a Welding power supply to create an Electric arc between an electrode and the base material to melt the metals at the welding point Lightning is an atmospheric discharge of Electricity, which typically occurs during Thunderstorms and sometimes during volcanic eruptions or X-radiation (composed of X-rays) is a form of Electromagnetic radiation. 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.

Curing of inks, adhesives, varnishes and coatings

Certain inks, coatings and adhesives are formulated with photoinitiators and resins. Glue or adhesive is a compound that adheres or bonds two items together When exposed to the correct energy and irradiance in the required band of UV light, polymerization occurs, and so the adhesives harden or cure. Usually, this reaction is very quick, a matter of a few seconds. Applications include glass and plastic bonding, optical fiber coatings, the coating of flooring, UV Coating and paper finishes in offset printing, and dental fillings. An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length The term "UV coating" has various meanings Ultra-violet coating of paper Ultra-violet cured coatings can be applied over ink printed on paper and dried by exposure Printing is a process for reproducing text and image typically with ink on Paper using a printing press

An industry has developed around the manufacture of UV lamps sourced for UV curing applictions. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays 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) based bulbs are used which can be energised with electric arc or microwaves. Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Lower power fluorescent lamps 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 fibre optic light guides.

Radtech is a trade association dedicated to the promotion of this technology.

Deterring substance abuse in public places

UV lights have been installed in some parts of the world in public restrooms, and on public transport, for the purpose of deterring substance abuse. The blue color of these lights, combined with the fluorescence of the skin, make it harder for intravenous drug users to find a vein. ^[26] The efficacy of these lights for that purpose has been questioned, with some suggesting that drug users simply find a vein outside the public restroom and mark the spot with a marker for accessibility when inside the restroom. There is currently no published evidence supporting the idea of a deterrent effect.

Sun tanning

Sun tanning describes a darkening of the skin in a natural physiological response stimulated by exposure to ultraviolet radiation from sunshine (or a sunbed). Sun tanning describes a darkening of the skin (especially of fair-skinned individuals in a natural physiological response stimulated by exposure to ultraviolet (UV radiation Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun. A tanning bed or sunbed is a device emitting Ultraviolet radiation (typically 95% UVA and 5% UVB +/-3% used to produce a cosmetic tan. With excess exposure to the sun, a suntanned area can also develop sunburn. The increased production of melanin is triggered by the direct DNA damage. Direct DNA damage can occur when DNA directly absorbs the UV-B-photon ^[27] This kind of damage is recognized by the body and as a defense against UV radiation the skin produces more melanin. Melanin dissipates the UV energy as harmless heat, and therefore it is an excellent photoprotectant. The term Photoprotection designates the mechanisms that nature has developed to minimize the damages that the human body suffers when exposed to UV-irradiation Melanin protects against the direct DNA damage and against the indirect DNA damage. Indirect DNA damage occurs when a UV-photon is absorbed in the human skin by a Chromophore that does not have the ability to convert the energy into Sunscreen protects only against the direct DNA damage, but increases the indirect DNA damage^[14][15][16] - this causes the higher amount of melanoma that had been found repeatedly in sunscreen users compared to non-users. ^{[28][29][12][30][31]}

Erasing EPROM modules

Some EPROM (electronically programmable read-only memory) modules are erased by exposure to UV radiation. An EPROM, or E rasable P rogrammable '''''R'''ead-'''O'''nly '''M'''emory'', is a type of memory chip that retains its These modules often have a transparent glass (quartz) window on the top of the chip that allows the UV radiation in. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in These have been largely superseded by EEPROM and flash memory chips in most devices. EEPROM (also written E2PROM and pronounced e-e-prom or simply e-squared which stands for E lectrically E rasable P rogrammable Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed

Preparing low surface energy polymers

UV radiation is useful in preparing low surface energy polymers for adhesives. Polymers exposed to UV light will oxidize thus raising the surface energy of the polymer. Once the surface energy of the polymer has been raised, the bond between the adhesive and the polymer will not be smaller.

Reading otherwise illegible papyruses

Using multi-spectral imaging it is possible to read illegible papyruses, such as the burned papyruses of the Villa of the Papyri or of Oxyrhynchus. Papyrus (/pəˈpaɪrəs/ (Rhymes -aɪrəs)is a thick paper-like material produced from the Pith of the papyrus plant Cyperus papyrus The Villa of the Papyri is a private house in the ancient Roman city of Herculaneum (current commune of Ercolano) Oxyrhynchus (Ὀξύρρυγχος "sharp-nosed" ancient Egyptian Pr-Medjed; Coptic Pemdje; modern Egyptian Arabic The technique involves taking pictures of the illegible papyruses using different filters in the infrared or ultraviolet range, finely tuned to capture certain wavelengths of light. Thus, the optimum spectral portion can be found for distinguishing ink from paper on the papyrus surface.

Lasers

Ultraviolet lasers have applications in industry (laser engraving), medicine (dermatology and keratectomy), free air secure communications and computing (optical storage). A laser is a device that emits Light ( Electromagnetic radiation) through a process called Stimulated emission. Laser engraving is the practice of using Lasers to engrave or mark an object Dermatology (from Greek grc δέρμα derma, "skin" and grc -λογία -logia) is a branch of Medicine dealing with Photorefractive keratectomy (PRK and Laser-Assisted Sub-Epithelial Keratectomy (or Laser Epithelial Keratomileusis) (LASEK are Laser Eye surgery In Telecommunications Free Space Optics (FSO is an Optical communication technology that uses light propagating in free space to transmit data between two points Optical storage is a term from Engineering referring to the storage of data on an optically readable medium They can be made by applying frequency conversion to lower-frequency lasers, or from Ce:LiSAF crystals (cerium doped with lithium strontium aluminum fluoride), a process developed in the 1990s at Lawrence Livermore National Laboratory. Nonlinear optics (NLO is the branch of Optics that describes the behaviour of Light in nonlinear media, that is media in which the dielectric polarization Cerium (ˈsɪəriəm is a Chemical element with the symbol Ce and Atomic number 58 A dopant, also called doping agent and dope, is an impurity element added to a crystal or semiconductor lattice in low concentrations in order to alter the optical/electrical The Lawrence Livermore National Laboratory ( LLNL) in Livermore California is a scientific research laboratory founded by the University of California in 1952 ^[32]

Evolutionary significance

Evolution of early reproductive proteins and enzymes is attributed in modern models of evolutionary theory to ultraviolet light. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins UVB light causes thymine base pairs next to each other in genetic sequences to bond together into thymine dimers, a disruption in the strand which reproductive enzymes cannot copy (see picture above). Thymine is one of the four bases in the Nucleic acid of DNA that make up the letters ATGC A thymine dimer is the covalent bonding of two adjacent Thymine residues within a DNA molecule often catalyzed by ultraviolet radiation or chemical mutagenic agents This leads to frameshifting during genetic replication and protein synthesis, usually killing the organism. A frameshift mutation (also called a framing error) is a genetic Mutation caused by Indels ie Protein synthesis is the creation of proteins using DNA and' RNA'. As early prokaryotes began to approach the surface of the ancient oceans, before the protective ozone layer had formed, blocking out most wavelengths of UV light, they almost invariably died out. The few that survived had developed enzymes which verified the genetic material and broke up thymine dimer bonds, known as excision repair enzymes. A thymine dimer is the covalent bonding of two adjacent Thymine residues within a DNA molecule often catalyzed by ultraviolet radiation or chemical mutagenic agents Many enzymes and proteins involved in modern mitosis and meiosis are extremely similar to excision repair enzymes, and are believed to be evolved modifications of the enzymes originally used to overcome UV light. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half ^[33]

See also

• UV index
• High-energy visible light
• Sun tanning
• Black light
• Wood's lamp
• Tanning lamp
• UV degradation
• UV Stabilizers in plastics
• Ultraviolet photography

References

External link

• Ultraviolet radiation biology

Further reading

• Hu, S; Ma, F; Collado-Mesa, F & Kirsner, R. S. (2004), “UV radiation, latitude, and melanoma in US Hispanics and blacks”, Arch. Dermatol. 140 (7): 819-824, doi:10.1001/archderm.140.7.819, <http://archderm.ama-assn.org/cgi/content/full/140/7/819> 
• Hockberger, Philip E. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. , “A History of Ultraviolet Photobiology for Humans, Animals and Microorganisms”, Photochemisty and Photobiology 76 (6): 561-569, doi:10.1562/0031-8655(2002)076<0561:AHOUPF>2.0.CO;2, <http://www.bioone.org/archive/0031-8655/76/6/pdf/i0031-8655-76-6-561.pdf> 
• Allen, Jeannie (2001-09-06), Ultraviolet Radiation: How it Affects Life on Earth, Earth Observatory, NASA, USA, <http://earthobservatory.nasa.gov/Library/UVB/>