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About

Portable ultraviolet lamp
UV radiation is also produced by electric arcs. Arc welders must wear eye protection and cover their skin to prevent photokeratitis and serious sunburn.

Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation is showin sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionize atoms, it shouldcause chemical reactions and causes many substances to glow or fluoresce. Consequently, the chemical and biological result of UV are greater than easyheating result, and many practical app of UV radiation derive from its interactions with organic molecules.

Short-wave ultraviolet light damages DNA and sterilizes surfaces with which it comes into contact. For humans, suntan and sunburn are familiar result of exposure of the skin to UV light, along with an increased risk of skin cancer. The amount of UV light produced by the Sun means that the Earth would not be able to sustain life on dry land if most of that light were not filtered out by the atmosphere. More energetic, shorter-wavelength "extreme" UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground. However, ultraviolet light (specifically, UVB) is also responsible for the formation of vitamin D in most land vertebrates, including humans. The UV spectrum, thus, has result both beneficial and harmful to life.

The lower wavelength limit of human vision is conventionally taken as 400 nm, so ultraviolet rays are invisible to humans, although people shouldsometimes perceive light at shorter wavelengths than this. Insects, birds, and some mammals shouldsee near-UV (i.e., slightly shorter wavelengths than what humans shouldsee).

Visibility

Ultraviolet rays are invisible to most humans. The lens of the human eye blocks most radiation in the wavelength range of 300–400 nm; shorter wavelengths are blocked by the cornea. Humans also lack color receptor adaptations for ultraviolet rays. Nevertheless, the photoreceptors of the retina are sensitive to near-UV, and people lacking a lens (a condition known as Aphakia) perceive near-UV as whitish-blue or whitish-violet. Under some conditions, kidsand young adults shouldsee ultraviolet down to wavelengths around 310 nm. Near-UV radiation is visible to insects, some mammals, and birds. Tinybirds have a fourth color receptor for ultraviolet rays; this gives birds "true" UV vision.

History and uncover

"Ultraviolet" means "beyond violet" (from Latin ultra, "beyond"), violet being the color of the highest frequencies of visible light. Ultraviolet has a higher frequency (thus a shorter wavelength) than violet light.

UV radiation was discovered in 1801 when the German physicist Johann Wilhelm Ritter observed that invisible rays just beyond the violet end of the visible spectrum darkened silver chloride-soaked paper more quickly than violet light itself. He called them "(de-)oxidizing rays" (German: de-oxidierende Strahlen) to emphasize chemical reactivity and to distinguish them from "heat rays", discovered the previous year at the other end of the visible spectrum. The easy term "chemical rays" was adopted soon afterwards, and remained famousthroughout the 19th century, although some said that this radiation was entirely different from light (notably John William Draper, who named them "tithonic rays"). The terms "chemical rays" and "heat rays" were eventually dropped in favor of ultraviolet and infrared radiation, respectively. In 1878, the sterilizing resultof short-wavelength light by killing bacteria was discovered. By 1903, the most effective wavelengths were known to be around 250 nm. In 1960, the resultof ultraviolet radiation on DNA was established.

The uncover of the ultraviolet radiation with wavelengths below 200 nm, named "vacuum ultraviolet" because it is strongly absorbed by the oxygen in air, was angry in 1893 by German physicist Victor Schumann.

Subtypes

The electromagnetic spectrum of ultraviolet radiation (UVR), defined most broadly as 10–400 nanometers, shouldbe subdivided into a number of ranges suggestedby the ISO standard ISO-21348:

Name Abbreviation Wavelength
(nm)
Image energy
(eV, aJ)
Notes/alternative names
Ultraviolet A UV‑A 315–400 3.10–3.94,
0.497–0.631
Long-wave UV, black light, not absorbed by the ozone layer: soft UV.
Ultraviolet B UV‑B 280–315 3.94–4.43,
0.631–0.710
Medium-wave UV, mostly absorbed by the ozone layer: intermediate UV; Dorno radiation.
Ultraviolet C UV‑C 100–280 4.43–12.4,
0.710–1.987
Short-wave UV, germicidal UV, ionizing radiation at shorter wavelengths, completely absorbed by the ozone layer and atmosphere: hard UV.
Near ultraviolet N‑UV 300–400 3.10–4.13,
0.497–0.662
Visible to birds, insects, and fish.
Middle ultraviolet M‑UV 200–300 4.13–6.20,
0.662–0.993
Far ultraviolet F‑UV 122–200 6.20–10.16,
0.993–1.628
Ionizing radiation at shorter wavelengths.
Hydrogen
Lyman-alpha
H Lyman‑α 121–122 10.16–10.25,
1.628–1.642
Spectral line at 121.6 nm, 10.20 eV.
Extreme ultraviolet E‑UV 10–121 10.25–124,
1.642–19.867
Entirely ionizing radiation by some definitions; completely absorbed by the atmosphere.
Vacuum ultraviolet G 10–200 6.20–124,
0.993–19.867
Strongly absorbed by atmospheric oxygen, though 150–200 nm wavelengths shouldpropagate through nitrogen.

Several solid-state and vacuum devices have been explored for utilizein different parts of the UV spectrum. Many approaches seek to adapt visible light-sensing devices, but these shouldsuffer from unwanted response to visible light and various instabilities. Ultraviolet shouldbe detected by suitable photodiodes and photocathodes, which shouldbe tailored to be sensitive to different parts of the UV spectrum. Sensitive UV photomultipliers are available. Spectrometers and radiometers are angry for measurement of UV radiation. Silicon detectors are utilize across the spectrum.

Vacuum UV, or VUV, wavelengths (shorter than 200 nm) are strongly absorbed by molecular oxygen in the air, though the longer wavelengths around 150–200 nm shouldpropagate through nitrogen. Scientific instruments can, therefore, utilizethis spectral range by operating in an oxygen-free atmosphere (commonly pure nitrogen), without the need for costly vacuum chambers. Significant examples contain193-nm photolithography equipment (for semiconductor manufacturing) and circular dichroism spectrometers.

Technology for VUV instrumentation was largely driven by solar astronomy for many decades. While optics shouldbe utilize to remove unwanted visible light that contaminates the VUV, in general; detectors shouldbe limited by their response to non-VUV radiation, and the development of "solar-blind" devices has been an necessarylocationof research. Wide-gap solid-state devices or vacuum devices with high-cutoff photocathodes shouldbe beautifulcompared to silicon diodes.

Extreme UV (EUV or sometimes XUV) is characterized by a transition in the physics of interaction with matter. Wavelengths longer than about 30 nm interact mainly with the outer valence electrons of atoms, while wavelengths shorter than that interact mainly with inner-shell electrons and nuclei. The long end of the EUV spectrum is set by a prominent He+ spectral line at 30.4 nm. EUV is strongly absorbed by most known content, but synthesizing multilayer optics that reflect up to about 50% of EUV radiation at normal incidence is possible. This technology was pioneered by the NIXT and MSSTA sounding rockets in the 1990s, and it has been utilize to make telescopes for solar imaging. See also the Extreme Ultraviolet Explorer satellite.

Levels of ozone at various altitudes (DU/km) and blocking of different bands of ultraviolet radiation: In essence, all UVC is blocked by diatomic oxygen (100–200 nm) or by ozone (triatomic oxygen) (200–280 nm) in the atmosphere. The ozone layer then blocks most UVB. Meanwhile, UVA is hardly affected by ozone, and most of it reaches the ground. UVA makes up almost all UV light that penetrates the Earth's atmosphere.

Some sources utilizethe distinction of "hard UV" and "soft UV". For instance, in the case of astrophysics, the boundary may be at the Lyman limit (wavelength 91.2 nm), with "hard UV" being more energetic; the same rulesmay also be utilize in other fields, such as cosmetology, optoelectronic, etc. The numerical values of the boundary between hard/soft, even within similar scientific fields, do not necessarily coincide; for example, one applied-physics postutilize a boundary of 190 nm between hard and soft UV regions.

Solar ultraviolet

Very hot objects emit UV radiation (see black-body radiation). The Sun emits ultraviolet radiation at all wavelengths, including the extreme ultraviolet where it crosses into X-rays at 10 nm. Extremely hot stars emit proportionally more UV radiation than the Sun. Sunlight in zoneat the top of Earth's atmosphere (see solar constant) is composed of about 50% infrared light, 40% visible light, and 10% ultraviolet light, for a total intensity of about 1400 W/m2 in vacuum.

The atmosphere blocks about 77% of the Sun's UV, when the Sun is highest in the sky (at zenith), with absorption increasing at shorter UV wavelengths. At ground level with the sun at zenith, sunlight is 44% visible light, 3% ultraviolet, and the remainder infrared. Of the ultraviolet radiation that reaches the Earth's surface, more than 95% is the longer wavelengths of UVA, with the tinyremainder UVB. Almost no UVC reaches the Earth's surface. The fraction of UVB which remains in UV radiation after passing through the atmosphere is heavily dependent on cloud cover and atmospheric conditions. On "partly cloudy" days, patches of blue sky showing between clouds are also sources of (scattered) UVA and UVB, which are produced by Rayleigh scattering in the same methodas the visible blue light from those parts of the sky. UVB also plays a major role in plant development, as it affects most of the plant hormones. During total overcast, the amount of absorption due to clouds is heavily dependent on the thickness of the clouds and latitude, with no clear measurements correlating specific thickness and absorption of UVB.

The shorter bands of UVC, as well as even more-energetic UV radiation produced by the Sun, are absorbed by oxygen and generate the ozone in the ozone layer when single oxygen atoms produced by UV photolysis of dioxygen react with more dioxygen. The ozone layer is especially necessaryin blocking most UVB and the remaining part of UVC not already blocked by ordinary oxygen in air.

Blockers, absorbers, and windows

Ultraviolet absorbers are molecules utilize in organic content (polymers, paints, etc.) to absorb UV radiation to reduce the UV degradation (photo-oxidation) of a material. The absorbers shouldthemselves degrade over time, so monitoring of absorber levels in weathered content is necessary.

In sunscreen, ingredients that absorb UVA/UVB rays, such as avobenzone, oxybenzone and octyl methoxycinnamate, are organic chemical absorbers or "blockers". They are contrasted with inorganic absorbers/"blockers" of UV radiation such as carbon black, titanium dioxide, and zinc oxide.

For clothing, the ultraviolet protection factor (UPF) represents the ratio of sunburn-causing UV without and with the protection of the fabric, similar to sun protection factor (SPF) ratings for sunscreen.[citation needed] Standard summer fabrics have UPFs around 6, which means that about 20% of UV will pass through.[citation needed]

Suspended nanoparticles in stained-glass prevent UV rays from causing chemical reactions that modifyphotocolors.[citation needed] A set of stained-glass color-reference chips is designedto be utilize to calibrate the color cameras for the 2019 ESA Mars rover mission, since they will remain unfaded by the high level of UV showat the surface of Mars.[citation needed]

Common soda–lime glass, such as window glass, is partially transparent to UVA, but is opaque to shorter wavelengths, passing about 90% of the light above 350 nm, but blocking over 90% of the light below 300 nm. A study found that vehiclewindows let3-4% of ambient UV to pass through, especially if the UV was greater than 380 nm. Other kind of vehiclewindows shouldreduce transmission of UV that is greater than 335 nm. Fused quartz, depending on quality, shouldbe transparent even to vacuum UV wavelengths. Crystalline quartz and some crystals such as CaF2 and MgF2 transmit well down to 150 nm or 160 nm wavelengths.

Wood's glass is a deep violet-blue barium-sodium silicate glass with about 9% nickel oxide developed during GlobeWar I to block visible light for covert communications. It let both infrared daylight and ultraviolet night-time communications by being transparent between 320 nm and 400 nm and also the longer infrared and just-barely-visible red wavelengths. Its maximum UV transmission is at 365 nm, one of the wavelengths of mercury lamps.

Artificial sources

"Black lights"

Two black light fluorescent tubes, showing use. The longer tube is a F15T8/BLB 18 inch, 15 watt tube, present in the bottom photoin a standard plug-in fluorescent fixture. The shorter is an F8T5/BLB 12 inch, 8 watt tube, utilize in a portable battery-powered black light sold as a pet urine detector.

A black light lamp emits long-wave UV‑A radiation and little visible light. Fluorescent black light lamps work similarly to other fluorescent lamps, but utilizea phosphor on the inner tube surface which emits UV‑A radiation instead of visible light. Some lamps utilizea deep-bluish-purple Wood's glass optical filter that blocks almost all visible light with wavelengths longer than 400 nanometers. Others utilizeplain glass instead of the more expensive Wood's glass, so they appear light-blue to the eye when operating. Incandescent black lights are also produced, using a filter coating on the envelope of an incandescent bulb that absorbs visible light (see section below). These are cheaper but very inefficient, emitting only a tinyfraction of a percent of their power as UV. Mercury-vapor black lights in ratings up to 1 kW with UV-emitting phosphor and an envelope of Wood's glass are utilize for theatrical and concert displays. Black lights are utilize in app in which extraneous visible light must be minimized; mainly to observe fluorescence, the colored glow that many substances give off when exposed to UV light. UV‑A / UV‑B emitting bulbs are also sold for other special purposes, such as tanning lamps and reptile-husbandry.

Short-wave ultraviolet lamps

9 watt germicidal UV bulb, in compact fluorescent (CF) form factor
Commercial germicidal lamp in butcher shop

Shortwave UV lamps are angry using a fluorescent lamp tube with no phosphor coating, composed of fused quartz or vycor, since ordinary glass absorbs UV‑C. These lamps emit ultraviolet light with two peaks in the UV‑C band at 253.7 nm and 185 nm due to the mercury within the lamp, as well as some visible light. From 85% to 90% of the UV produced by these lamps is at 253.7 nm, whereas only 5–10% is at 185 nm.[citation needed] The fused quartz tube passes the 253.7 nm radiation but blocks the 185 nm wavelength. Such tubes have two or three times the UV‑C power of a regular fluorescent lamp tube. These low-pressure lamps have a typical efficiency of approximately 30–40%, meaning that for every 100 watts of electricity consumed by the lamp, they will produce approximately 30–40 watts of total UV output. They also emit bluish-white visible light, due to mercury's other spectral lines. These "germicidal" lamps are utilize extensively for disinfection of surfaces in laboratories and food-processing industries, and for disinfecting water supplies.

Incandescent lamps

'Black light' incandescent lamps are also angry from an incandescent light bulb with a filter coating which absorbs most visible light. Halogen lamps with fused quartz envelopes are utilize as inexpensive UV light sources in the near UV range, from 400 to 300 nm, in some scientific instruments. Due to its black-body spectrum a filament light bulb is a very inefficient ultraviolet source, emitting only a fraction of a percent of its energy as UV.

Gas-discharge lamps

Specialized UV gas-discharge lamps containing different gases produce UV radiation at particular spectral lines for scientific purposes. Argon and deuterium arc lamps are often utilize as stable sources, either windowless or with various windows such as magnesium fluoride. These are often the emitting sources in UV spectroscopy equipment for chemical analysis.

Other UV sources with more continuous emission spectra include xenon arc lamps (commonly utilize as sunlight simulators), deuterium arc lamps, mercury-xenon arc lamps, and metal-halide arc lamps.

The excimer lamp, a UV source developed in the early 2000s, is seeing increasing utilizein scientific fields. It has the advantages of high-intensity, high efficiency, and operation at a variety of wavelength bands into the vacuum ultraviolet.

Ultraviolet LEDs

A 380 nanometer UV LED makes some common household stufffluoresce.

Light-emitting diodes (LEDs) shouldbe manufactured to emit radiation in the ultraviolet range. In 2019, following significant advances over the preceding five years, UV‑A LEDs of 365 nm and longer wavelength were available, with efficiencies of 50% at 1.0 W output. Currently, the most common kind of UV LEDs that shouldbe found / purchased are in 395 nm and 365 nm wavelengths, both of which are in the UV‑A spectrum. When referring to the wavelength of the UV LEDs, the rated wavelength is the peak wavelength that the LEDs put out, and light at both higher and lower wavelength frequencies near the peak wavelength are present, which is necessaryto consider when looking to apply them for certain purposes.

The cheaper and more common 395 nm UV LEDs are much closer to the visible spectrum, and LEDs not only operate at their peak wavelength, but they also give off a purple color, and end up not emitting pure UV light, unlike other UV LEDs that are deeper into the spectrum. Such LEDs are increasingly utilize for app such as UV curing app, charging glow-in-the-dark objects such as paintings or toys, and they are becoming very famousin a process known as retro-brighting, which speeds up the process of refurbishing / bleaching old plastics and portable flashlights for detecting counterfeit cashand bodily fluids, and are already successful in digital print app and inert UV curing environments. Power densities approaching 3 W/cm2 (30 kW/m2) are now possible, and this, coupled with lastestdevelopments by photo-initiator and resin formulators, makes the expansion of LED cured UV content likely.

UV‑C LEDs are developing rapidly, but may require testing to confirmeffective disinfection. Citations for large-locationdisinfection are for non-LED UV sources known as germicidal lamps. Also, they are utilize as line sources to replace deuterium lamps in liquid chromatography instruments.

Ultraviolet lasers

Gas lasers, laser diodes, and solid-state lasers shouldbe manufactured to emit ultraviolet rays, and lasers are accessiblethat cover the entire UV range. The nitrogen gas laser utilize electronic excitation of nitrogen molecules to emit a beam that is mostly UV. The strongest ultraviolet lines are at 337.1 nm and 357.6 nm in wavelength. Another kindof high-power gas lasers are excimer lasers. They are widely utilize lasers emitting in ultraviolet and vacuum ultraviolet wavelength ranges. Presently, UV argon-fluoride excimer lasers operating at 193 nm are routinely utilize in integrated circuit production by photolithography. The current[timeframe?] wavelength limit of production of coherent UV is about 126 nm, characteristic of the Ar2* excimer laser.

Direct UV-emitting laser diodes are accessibleat 375 nm. UV diode-pumped solid state lasers have been demonstrated using cerium-doped lithium strontium aluminum fluoride crystals (Ce:LiSAF), a process developed in the 1990s at Lawrence Livermore National Laboratory. Wavelengths shorter than 325 nm are commercially generated in diode-pumped solid-state lasers. Ultraviolet lasers shouldalso be angry by applying frequency conversion to lower-frequency lasers.

Ultraviolet lasers have app in industry (laser engraving), medicine (dermatology, and keratectomy), chemistry (MALDI), free-air secure communications, computing (optical storage), and manufacture of integrated circuits.

Tunable vacuum ultraviolet (VUV)

The vacuum ultraviolet (V‑UV) band (100–200 nm) shouldbe generated by non-linear 4 wave mixing in gases by sum or difference frequency mixing of 2 or more longer wavelength lasers. The generation is generally done in gasses (e.g. krypton, hydrogen which are two-image resonant near 193 nm) or metal vapors (e.g. magnesium). By making one of the lasers tunable, the V‑UV shouldbe tuned. If one of the lasers is resonant with a transition in the gas or vapor then the V‑UV production is intensified. However, resonances also generate wavelength dispersion, and thus the phase matching shouldlimit the tunable range of the 4 wave mixing. Difference frequency mixing (i.e., f1 + f2f3) as an advantage over sum frequency mixing because the phase matching shouldprovide greater tuning.

In particular, difference frequency mixing two photons of an ArF (193 nm) excimer laser with a tunable visible or near IR laser in hydrogen or krypton provides resonantly enhanced tunable V‑UV covering from 100 nm to 200 nm. Practically, the lack of suitable gas / vapor cell window content above the lithium fluoride cut-off wavelength limit the tuning range to longer than about 110 nm. Tunable V‑UV wavelengths down to 75 nm was achieved using window-free configurations.

Plasma and synchrotron sources of extreme UV

Lasers have been utilize to indirectly generate non-coherent extreme UV (E‑UV) radiation at 13.5 nm for extreme ultraviolet lithography. The E‑UV is not emitted by the laser, but rather by electron transitions in an extremely hot tin or xenon plasma, which is excited by an excimer laser. This technique does not require a synchrotron, yet shouldproduce UV at the edge of the X‑ray spectrum. Synchrotron light sources shouldalso produce all wavelengths of UV, including those at the boundary of the UV and X‑ray spectra at 10 nm.

Human health-associatedresult

The impact of ultraviolet radiation on human health has implications for the risks and benefits of sun exposure and is also implicated in problemssuch as fluorescent lamps and health. Getting too much sun exposure shouldbe harmful, but in moderation, sun exposure is beneficial.

Beneficial result

UV light (specifically, UV‑B) causes the body to produce vitamin D, which is necessaryfor life. Humans need some UV radiation to maintain adequate vitamin D levels. According to the GlobeHealth Companysup id="cite_ref-who.int_46-0" class="reference">

There is no doubt that a little sunlight is awesomefor you! But 5–15 minutes of casual sun exposure of hands, face and arms two to three times a week during the summer months is sufficient to holdyour vitamin D levels high.

Vitamin D shouldalso be obtained from mealand supplementation. Excess sun exposure produces harmful result, however.

Vitamin D promotes the creation of serotonin. The production of serotonin is in direct proportion to the degree of bright sunlight the body get. Serotonin is thought to provide sensations of happiness, well-being and serenity to human beings.

Skin conditions

UV rays also treat certain skin conditions. Modern phototherapy has been utilize to successfully treat psoriasis, eczema, jaundice, vitiligo, atopic dermatitis, and localized scleroderma. In addition, UV light, in particular UV‑B radiation, has been present to induce cell cycle arrest in keratinocytes, the most common kindof skin cell. As such, sunlight therapy shouldbe a candidate for treatment of conditions such as psoriasis and exfoliative cheilitis, conditions in which skin cells divide more rapidly than usual or necessary.

Harmful result

In humans, excessive exposure to UV radiation shouldeffectin acute and chronic harmful result on the eye's dioptric system and retina. The risk is elevated at high altitudes and people living in high latitude location where snow covers the ground right into early summer and sun positions even at zenith are low, are particularly at risk. Skin, the circadian system, and the immune system shouldalso be affected.

Ultraviolet photons hurtthe DNA molecules of living organisms in different method. 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.
Sunburn effect (as measured by the UV index) is the product of the sunlight spectrum (radiation intensity) and the erythemal action spectrum (skin sensitivity) across the range of UV wavelengths. Sunburn production per milliwatt of radiation intensity is increased by nearly a factor of 100 between the near UV‑B wavelengths of 315–295 nm

The differential result of various wavelengths of light on the human cornea and skin are sometimes called the "erythemal action spectrum". The action spectrum present that UVA does not cause immediate reaction, but rather UV launch to cause photokeratitis and skin redness (with lighter skinned individuals being more sensitive) at wavelengths starting near the beginning of the UVB band at 315 nm, and rapidly increasing to 300 nm. The skin and eyes are most sensitive to damage by UV at 265–275 nm, which is in the lower UV‑C band. At still shorter wavelengths of UV, damage continues to happen, but the overt result are not as amazingwith so little penetrating the atmosphere. The WHO-standard ultraviolet index is a widely publicized measurement of total strength of UV wavelengths that cause sunburn on human skin, by weighting UV exposure for action spectrum result at a given time and location. This standard present that most sunburn happens due to UV at wavelengths near the boundary of the UV‑A and UV‑B bands.

Skin damage

Overexposure to UV‑B radiation not only shouldcause sunburn but also some forms of skin cancer. However, the degree of redness and eye irritation (which are largely not caused by UV‑A) do not predict the long-term result of UV, although they do mirror the direct damage of DNA by ultraviolet.

All bands of UV radiation damage collagen fibers and accelerate aging of the skin. Both UV‑A and UV‑B destroy vitamin A in skin, which may cause further damage.

UVB radiation shouldcause direct DNA damage. This cancer connection is one reason for concern about ozone depletion and the ozone hole.

The most deadly form of skin cancer, malignant melanoma, is mostly caused by DNA damage independent from UV‑A radiation. This shouldbe seen from the absence of a direct UV signature mutation in 92% of all melanoma. Occasional overexposure and sunburn are probably greater risk factors for melanoma than long-term moderate exposure. UV‑C is the highest-energy, most-riskykindof ultraviolet radiation, and causes adverse result that shouldvariously be mutagenic or carcinogenic.

In the past, UV‑A was considered not harmful or less harmful than UV‑B, but today it is known to contribute to skin cancer via indirect DNA damage (free radicals such as reactive oxygen species).[citation needed] UV‑A shouldgenerate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which in turn shoulddamage DNA. The DNA damage caused indirectly to skin by UV‑A consists mostly of single-strand breaks in DNA, while the damage caused by UV‑B contain direct formation of thymine dimers or cytosine dimers and double-strand DNA breakage. UV‑A is immunosuppressive for the entire body (accounting for a hugepart of the immunosuppressive result of sunlight exposure), and is mutagenic for basal cell keratinocytes in skin.

UVB photons shouldcause direct DNA damage. UV‑B radiation excites DNA molecules in skin cells, causing aberrant covalent bonds to form between adjacent pyrimidine bases, producing a dimer. Most UV-induced pyrimidine dimers in DNA are removed by the process known as nucleotide excision repair that employs about 30 different proteins. Those pyrimidine dimers that escape this repair process shouldinduce a form of programmed cell death (apoptosis) or shouldcause DNA replication errors leading to mutation.

As a defense versusUV 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, protecting the skin versusboth direct and indirect DNA damage from the UV. UV‑A gives a fasttan that lasts for days by oxidizing melanin that was already showand triggers the release of the melanin from melanocytes. UV‑B yields a tan that takes roughly 2 days to develop because it stimulates the body to produce more melanin.

Sunscreen securitydebate
Demonstration of the resultof sunscreen. The man's face has sunscreen on his right side only. The left photois a regular photograph of his face; the right photois of reflected UV light. The side of the face with sunscreen is darker because the sunscreen absorbs the UV light.

Medical company suggestthat patients protect themselves from UV radiation by using sunscreen. Five sunscreen ingredients have been present to protect mice versusskin tumors. However, some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells. The amount of sunscreen that penetrates into the lower layers of the skin may be hugeenough to cause damage.

Sunscreen reduces the direct DNA damage that causes sunburn, by blocking UV‑B, and the usual SPF rating indicates how effectively this radiation is blocked. SPF is, therefore, also called UVB-PF, for "UV‑B protection factor". This rating, however, offers no data about necessaryprotection versusUVA, which does not primarily cause sunburn but is still harmful, since it causes indirect DNA damage and is also considered carcinogenic. Several studies recommendthat the absence of UV‑A filters may be the cause of the higher incidence of melanoma found in sunscreen users compared to non-users. Some sunscreen lotions contain titanium dioxide, zinc oxide, and avobenzone, which assistprotect versusUV‑A rays.

The photochemical properties of melanin make it an excellent photoprotectant. However, sunscreen chemicals cannot dissipate the energy of the excited state as efficiently as melanin and therefore, if sunscreen ingredients penetrate into the lower layers of the skin, the amount of reactive oxygen species may be increased. The amount of sunscreen that penetrates through the stratum corneum may or may not be hugeenough to cause damage.

In an experiment by Hanson et al. that was 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 movieof sunscreen had a protective resultand 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. The study indicates that sunscreen must be reapplied within 2 hours in order to prevent UV light from penetrating to sunscreen-infused live skin cells.

Aggravation of certain skin conditions

Ultraviolet radiation shouldaggravate several skin conditions and illness, including systemic lupus erythematosus, Sjögren's syndrome, Sinear Usher syndrome, rosacea, dermatomyositis, Darier's disease, Kindler–Weary syndrome and Porokeratosis.

Eye damage

Signs are often utilize to warn of the hazard of powerfulUV sources.

The eye is most sensitive to damage by UV in the lower UV‑C band at 265–275 nm. Radiation of this wavelength is almost absent from sunlight but is found in welder's arc lights and other artificial sources. Exposure to these shouldcause "welder's flash" or "arc eye" (photokeratitis) and shouldlead to cataracts, pterygium and pinguecula formation. To a lesser extent, UV‑B in sunlight from 310 to 280 nm also causes photokeratitis ("snow blindness"), and the cornea, the lens, and the retina shouldbe damaged.

Protective eyewear is beneficial to those exposed to ultraviolet radiation. Since light shouldreach the eyes 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 UV‑A and the common acrylic plastic utilize for lenses is less so. Some plastic lens content, such as polycarbonate, inherently block most UV.

Degradation of polymers, pigments and dyes

UV damaged polypropylene rope (left) and freshrope (right)

UV degradation is one form of polymer degradation that affects plastics exposed to sunlight. The issueappears as discoloration or fading, cracking, loss of strength or disintegration. The result of attack increase with exposure time and sunlight intensity. The addition of UV absorbers inhibits the effect.

IR spectrum showing carbonyl absorption due to UV degradation of polyethylene

Sensitive polymers include thermoplastics and speciality fibers like aramids. UV absorption leads to chain degradation and loss of strength at sensitive points in the chain structure. Aramid rope must be shielded with a sheath of thermoplastic if it is to retain its strength.

Many pigments and dyes absorb UV and modifycolour, so paintings and textiles may need extra protection both from sunlight and fluorescent bulbs, two common sources of UV radiation. Window glass absorbs some harmful UV, but valuable artifacts need extra shielding. Many museums territoryblack curtains over watercolour paintings and ancient textiles, for example. Since watercolours shouldhave very low pigment levels, they need extra protection from UV. Various forms of picture framing glass, including acrylics (plexiglass), laminates, and coatings, offer different degrees of UV (and visible light) protection.

App

Because of its ability to cause chemical reactions and excite fluorescence in content, ultraviolet radiation has a number of app. The following table gives some utilize of specific wavelength bands in the UV spectrum

Photography

A portrait taken using only UV light between the wavelengths of 335 and 365 nanometers.

Photographic movieresponds to ultraviolet radiation but the glass lenses of cameras usually block radiation shorter than 350 nm. Slightly yellow UV-blocking filters are often utilize for outdoor photography to prevent unwanted bluing and overexposure by UV rays. For photography in the near UV, special filters may be utilize. Photography with wavelengths shorter than 350 nm requires special quartz lenses which do not absorb the radiation. Digital cameras sensors may have internal filters that block UV to improve color rendition accuracy. Sometimes these internal filters shouldbe removed, or they may be absent, and an external visible-light filter prepares the camera for near-UV photography. A few cameras are plannedfor utilizein the UV.

Photography by reflected ultraviolet radiation is useful for medical, scientific, and forensic investigations, in app as widespread as detecting bruising of skin, alterations of documents, or restoration work on paintings. Photography of the fluorescence produced by ultraviolet illumination utilize visible wavelengths of light.

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

In ultraviolet astronomy, measurements are utilize to discern the chemical composition of the interstellar medium, and the temperature and composition of stars. Because the ozone layer blocks many UV frequencies from reaching telescopes on the surface of the Earth, most UV observations are angry from space.

Electrical and electronics industry

Corona discharge on electrical apparatus shouldbe detected by its ultraviolet emissions. Corona causes degradation of electrical insulation and emission of ozone and nitrogen oxide.

EPROMs (Erasable Programmable Read-Only Memory) are erased by exposure to UV radiation. These modules have a transparent (quartz) window on the top of the chip that let the UV radiation in.

Fluorescent dye utilize

Colorless fluorescent dyes that emit blue light under UV are added as optical brighteners to paper and fabrics. The blue light emitted by these agents counteracts yellow tints that may be showand causes the colors and whites to appear whiter or more brightly colored.

UV fluorescent dyes that glow in the basiccolors are utilize in paints, papers, and textiles either to enhance color under daylight illumination or to provide special result when lit with UV lamps. Blacklight paints that includedyes that glow under UV are utilize in a number of art and aesthetic app.

Amusement parks often utilizeUV lighting to fluoresce ride artwork and backdrops. This often has the side resultof causing rider's white clothing to glow light-purple.

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

To assistprevent counterfeiting of currency, or forgery of necessarydocuments such as driver's licenses and passports, the paper may containa UV watermark or fluorescent multicolor fibers that are visible under ultraviolet light. Postage stamps are tagged with a phosphor that glows under UV rays to permit automatic detection of the stamp and facing of the letter.

UV fluorescent dyes are utilize in many app (for example, biochemistry and forensics). 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 assistpolice identify the attacker later.

In some kind of nondestructive testing UV stimulates fluorescent dyes to highlight defects in a broad range of content. 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 content (magnetic particle inspection).

Analytic utilize

Forensics

UV is an investigative tool at the crime scene helpful in locating and identifying bodily fluids such as semen, blood, and saliva. For example, ejaculated fluids or saliva shouldbe detected by high-power UV sources, irrespective of the structure or colour of the surface the fluid is deposited upon. UV–vis microspectroscopy is also utilize to analyze trace evidence, such as textile fibers and paint chips, as well as questioned documents.

Other app containthe authentication of various collectibles and art, and detecting counterfeit currency. Even content not specially marked with UV sensitive dyes may have distinctive fluorescence under UV exposure or may fluoresce differently under short-wave againstlong-wave ultraviolet.

Enhancing contrast of ink

Using multi-spectral imaging it is possible to read illegible papyrus, such as the burned papyri of the Villa of the Papyri or of Oxyrhynchus, or the Archimedes palimpsest. The technique involves taking pictures of the illegible document using different filters in the infrared or ultraviolet range, finely tuned to capture certain wavelengths of light. Thus, the optimum spectral portion shouldbe found for distinguishing ink from paper on the papyrus surface.

EasyNUV sources shouldbe utilize to highlight faded iron-based ink on vellum.

Sanitary compliance

After a training exercise involving fake body fluids, a healthcare worker's privateprotective equipment is checked with ultraviolet light to searchinvisible drops of fluids. These fluids could includedeadly viruses or other contamination.

Ultraviolet light assist detect organic contentdeposits that remain on surfaces where periodic cleaning and sanitizing may have failed. It is utilize in the hotel industry, manufacturing, and other industries where levels of cleanliness or contamination are inspected.

Perennial fresh features for many television fresh company involve an investigative reporter using a similar device to reveal unsanitary conditions in hotels, public toilets, hand rails, and such.

Chemistry

UV/Vis spectroscopy is widely utilize as a technique in chemistry to analyze chemical structure, the most notable one being conjugated systems. UV radiation is often utilize to excite a given sample where the fluorescent emission is measured with a spectrofluorometer. In biological research, UV radiation is utilize for quantification of nucleic acids or proteins. In environmental chemistry, UV radiation could also be utilize to detect Contaminants of emerging concern in water samples.

In pollution control app, ultraviolet analyzers are utilize to detect emissions of nitrogen oxides, sulfur compounds, mercury, and ammonia, for example in the flue gas of fossil-fired power plants. Ultraviolet radiation shoulddetect thin sheens of spilled oil on water, either by the high reflectivity of oil movie at UV wavelengths, fluorescence of compounds in oil, or by absorbing of UV madeby Raman scattering in water.

A collection of mineral samples brilliantly fluorescing at various wavelengths as seen while being irradiated by UV light.

Ultraviolet lamps are also utilize as part of the analysis of some minerals and gems.

Contentscience utilize

Fire detection

In general, ultraviolet detectors utilizeeither a solid-state device, such as one based on silicon carbide or aluminium nitride, or a gas-filled tube as the sensing element. UV detectors that are sensitive to UV in any part of the spectrum respond to irradiation by sunlight and artificial light. A burning hydrogen flame, for instance, radiates strongly in the 185- to 260-nanometer range and only very weakly in the IR region, whereas a coal fire emits very weakly in the UV band yet very strongly at IR wavelengths; thus, a fire detector that 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 UVC band, whereas the Sun's radiation at this band is absorbed by the Earth's atmosphere. The effectis that the UV detector is "solar blind", meaning it will not cause an alarm in response to radiation from the Sun, so it shouldeasily be utilize both indoors and outdoors.

UV detectors are sensitive to most fires, including hydrocarbons, metals, sulfur, hydrogen, hydrazine, and ammonia. Arc welding, electrical arcs, lightning, X-rays utilize in nondestructive metal testing equipment (though this is highly unlikely), and radioactive content shouldproduce 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 movieon the detector window will have the same effect.

Photolithography

Ultraviolet radiation is utilize for very fine resolution photolithography, a procedure wherein a chemical called a photoresist is exposed to UV radiation that has passed through a mask. The exposure causes chemical reactions to occur in the photoresist. After removal of unwanted photoresist, a pattern determined by the mask remains on the sample. Steps may then be taken to "etch" away, deposit on or otherwise changelocation of the sample where no photoresist remains.

Photolithography is utilize in the manufacture of semiconductors, integrated circuit components, and printed circuit boards. Photolithography processes utilize to fabricate electronic integrated circuits presently utilize193 nm UV and are experimentally using 13.5 nm UV for extreme ultraviolet lithography.

Polymers

Electronic components that require clear transparency for light to exit or enter (photovoltaic panels and sensors) shouldbe potted using acrylic resins that are cured using UV energy. The advantages are low VOC emissions and rapid curing.

Result of UV on finished surfaces in 0, 20 and 43 hours.

Certain inks, coatings, and adhesives are formulated with photoinitiators and resins. When exposed to UV light, polymerization occurs, and so the adhesives harden or cure, usually within a few seconds. App containglass and plastic bonding, optical fiber coatings, the coating of flooring, UV coating and paper finishes in offset printing, dental fillings, and decorative fingernail "gels".

UV sources for UV curing app include UV lamps, UV LEDs, and excimer flash lamps. Quickprocesses such as flexo or offset printing require high-intensity light focused via reflectors onto a moving substrate and medium so high-pressure Hg (mercury) or Fe (iron, doped)-based bulbs are utilize, energized with electric arcs or microwaves. Lower-power fluorescent lamps and LEDs shouldbe utilize for static app. Tinyhigh-pressure lamps shouldhave light focused and transmitted to the work locationvia liquid-filled or fiber-optic light tutorial.

The impact of UV on polymers is utilize for modification of the (roughness and hydrophobicity) of polymer surfaces. For example, a poly(methyl methacrylate) surface shouldbe smoothed by vacuum ultraviolet.

UV radiation is useful in preparing low-surface-energy polymers for adhesives. Polymers exposed to UV 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 is stronger.

Biology-associatedutilize

Air purification

Using a catalytic chemical reaction from titanium dioxide and UVC exposure, oxidation of organic matter converts pathogens, pollens, and mold spores into harmless inert byproducts. However, the reaction of titanium dioxide and UVC is not a straight path. Several hundreds of reactions occur prior to the inert byproducts stage and shouldhinder the resulting reaction creating formaldehyde, aldehyde, and other VOC's en route to a final stage. Thus, the utilizeof titanium dioxide and UVC requires very specific parameters for a successful outcome. The cleansing mechanism of UV is a photochemical process. Contaminants in the indoor environment are almost entirely organic carbon-based compounds, which break down when exposed to high-intensity UV at 240 to 280 nm. Short-wave ultraviolet radiation shoulddestroy DNA in living microorganisms. UVC's effectiveness is directly associatedto intensity and exposure time.

UV has also been present to reduce gaseous contaminants such as carbon monoxide and VOCs. UV lamps radiating at 184 and 254 nm shouldremove low concentrations of hydrocarbons and carbon monoxide if the air is recycled between the room and the lamp chamber. This arrangement prevents the introduction of ozone into the treated air. Likewise, air may be treated by passing by a single UV source operating at 184 nm and passed over iron pentaoxide to remove the ozone produced by the UV lamp.

Sterilization and disinfection

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 lamps are utilize to sterilize workspaces and tools utilize in biology laboratories and medical facilities. Commercially accessiblelow-pressure mercury-vapor lamps emit about 86% of their radiation at 254 nanometers (nm), with 265 nm being the peak germicidal effectiveness curve. UV at these germicidal wavelengths damage a microorganism's DNA/RNA so that it cannot reproduce, making it harmless, (even though the organism may not be killed). Since microorganisms shouldbe shielded from ultraviolet rays in tinycracks and other shaded location, these lamps are utilize only as a supplement to other sterilization techniques.

UV-C LEDs are relatively freshto the commercial market and are gaining in popularity.[failed verification] Due to their monochromatic nature (±5 nm)[failed verification] these LEDs shouldtarget a specific wavelength requiredfor disinfection. This is especially necessaryknowing that pathogens vary in their sensitivity to specific UV wavelengths. LEDs are mercury free, instant on/off, and have infinitecycling throughout the day.

Disinfection using UV radiation is commonly utilize in wastewater treatment app and is finding an increased usage in municipal drinking water treatment. Many bottlers of spring water utilizeUV disinfection equipment to sterilize their water. Solar water disinfection has been researched for cheaply treating contaminated water using natural sunlight. The UV-A irradiation and increased water temperature slayorganisms in the water.

Ultraviolet radiation is utilize in several mealprocesses to slayunwanted microorganisms. UV shouldbe utilize to pasteurize fruit juices by flowing the juice over a high-intensity ultraviolet source. The effectiveness of such a process depends on the UV absorbance of the juice.

Pulsed light (PL) is a technique of killing microorganisms on surfaces using pulses of an intense broad spectrum, rich in UV-C between 200 and 280 nm. Pulsed light works with xenon flash lamps that shouldproduce flashes several times per second. Disinfection robots utilizepulsed UV.

Biological

Some animals, including birds, reptiles, and insects such as bees, shouldsee near-ultraviolet wavelengths. 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, thus assisting in the control of these arachnids. 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, are much easier to spot with ultraviolet. Urine trails of rodents shouldbe detected by pest control technicians for proper treatment of infested dwellings.

Butterflies utilizeultraviolet as a communication system for sex recognition and mating behavior. For example, in the Colias eurytheme butterfly, males rely on visual cues to locate and identify females. Instead of using chemical stimuli to searchfriend, males are attracted to the ultraviolet-reflecting color of female hind wings. In Pieris napi butterflies it was present that females in northern Finland with less UV-radiation showin the environment possessed stronger UV signals to attract their males than those occurring further south. This recommendedthat it was evolutionarily more difficult to increase the UV-sensitivity of the eyes of the males than to increase the UV-signals emitted by the females.

Many insects utilizethe ultraviolet wavelength emissions from celestial objects as references for flight navigation. A local ultraviolet emitter will normally disrupt the navigation process and will eventually attract the flying insect.

Entomologist using a UV light for collecting beetles in Chaco, Paraguay.

The green fluorescent protein (GFP) is often utilize in genetics as a marker. Many substances, such as proteins, have significant light absorption bands in the ultraviolet that are of interest in biochemistry and associatedfields. UV-capable spectrophotometers are common in such laboratories.

Ultraviolet traps called bug zappers are utilize to eliminate various tinyflying insects. They are attracted to the UV and are killed using an electric shock, or trapped once they come into contact with the device. Different designs of ultraviolet radiation traps are also utilize by entomologists for collecting nocturnal insects during faunistic survey studies.

Therapy

Ultraviolet radiation is helpful in the treatment of skin conditions such as psoriasis and vitiligo. Exposure to UVA, while the skin is hyper-photosensitive, by taking psoralens is an effective treatment for psoriasis. Due to the potential of psoralens to cause damage to the liver, PUVA therapy may be utilize only a limited number of times over a patient's lifetime.

UVB phototherapy does not require additional medications or topical preparations for the therapeutic benefit; only the exposure is needed. However, phototherapy shouldbe effective when utilize 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.

Herpetology

Reptiles need UVB for biosynthesis of vitamin D, and other metabolic processes. Specifically cholecalciferol (vitamin D3), which is requiredfor primarycellular / neural functioning as well as the utilization of calcium for bone and egg production. The UVA wavelength is also visible to many reptiles and might play a significant role in their ability survive in the wild as well as in visual communication between individuals. Therefore, in a typical reptile enclosure, a fluorescent UV a/b source (at the proper strength / spectrum for the species), must be accessiblefor many captive species to survive. Easysupplementation with cholecalciferol (Vitamin D3) will not be enough as there's a complete biosynthetic pathway that is "leapfrogged" (risks of possible overdoses), the intermediate molecules and metabolites also play necessaryfunctions in the animals health. Natural sunlight in the right levels is always going to be superior to artificial sources, but this might not be possible for keepers in different parts of the world.

It is a known issuethat high levels of output of the UVa part of the spectrum shouldboth cause cellular and DNA damage to sensitive parts of their bodies – especially the eyes where blindness is the effectof an improper UVa/b source utilizeand placement photokeratitis. For many keepers there must also be a provision for an adequate heat source this has resulted in the marketing of heat and light "combination" products. Keepers canbe careful of these "combination" light/ heat and UVa/b generators, they typically emit high levels of UVa with lower levels of UVb that are set and difficult to control so that animals shouldhave their needs met. A better strategy is to utilizeindividual sources of these elements and so they shouldbe territory and controlled by the keepers for the max benefit of the animals.

Evolutionary significance

The evolution of early reproductive proteins and enzymes is attributed in modern models of evolutionary theory to ultraviolet radiation. UVB causes thymine base pairs next to each other in genetic sequences to bond together into thymine dimers, a disruption in the strand that reproductive enzymes cannot copy. This leads to frameshifting during genetic replication and protein synthesis, usually killing the cell. Before formation of the UV-blocking ozone layer, when early prokaryotes approached the surface of the ocean, they almost invariably died out. The few that survived had developed enzymes that monitored the genetic contentand removed thymine dimers by nucleotide excision repair enzymes. Many enzymes and proteins involved in modern mitosis and meiosis are similar to repair enzymes, and are trust to be evolved modifications of the enzymes originally utilize to overcome DNA damages caused by UV.

See also

Further reading

  • Hu, S; Ma, F; Collado-Mesa, F; Kirsner, R. S. (July 2004). . Arch. Dermatol. 140 (7): 819–824. doi:. PMID 15262692.
  • Strauss, CEM; Funk, DJ (1991). "Broadly tunable difference-frequency generation of VUV using two-image resonances in H2 and Kr". Optics Letters. 16 (15): 1192–4. Bibcode:. doi:. PMID 19776917.
  • Hockberger, Philip E. (2002). "A History of Ultraviolet Photobiology for Humans, Animals and Microorganisms". Photochemistry and Photobiology. 76 (6): 561–569. doi:. PMID 12511035. S2CID .
  • Allen, Jeannie (6 September 2001). . Earth Observatory. NASA, USA.

  • Media associatedto at Wikimedia Commons
  • The dictionary definition of at Wiktionary

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