Ultraviolet

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UV-handlamp hg.jpg
Portable ultraviolet lamp
Pipefitter welder kutzo.jpg
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) designates a band of the electromagnetic spectrum with wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation is present in sunlight, and contributes about 10% of the total light output of 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 can cause chemical reactions and causes many substances to glow or fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules.

The electromagnetic spectrum is the range of frequencies of electromagnetic radiation and their respective wavelengths and photon energies.

Wavelength spatial period of the wave—the distance over which the waves shape repeats, and thus the inverse of the spatial frequency

In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is thus the inverse of the spatial frequency. Wavelength is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings and is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns. Wavelength is commonly designated by the Greek letter lambda (λ). The term wavelength is also sometimes applied to modulated waves, and to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids.

Sunlight portion of the electromagnetic radiation given off by the Sun

Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is filtered through Earth's atmosphere, and is obvious as daylight when the Sun is above the horizon. When the direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. When it is blocked by clouds or reflects off other objects, it is experienced as diffused light. The World Meteorological Organization uses the term "sunshine duration" to mean the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per square meter. Other sources indicate an "Average over the entire earth" of "164 Watts per square meter over a 24 hour day".

Contents

Suntan and sunburn are familiar effects of over-exposure of the skin to UV, along with higher risk of skin cancer. Living things on dry land would be severely damaged by ultraviolet radiation from the Sun if most of it were not filtered out by the Earth's atmosphere. [1] More energetic, shorter-wavelength "extreme" UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground. [2] Ultraviolet is also responsible for the formation of bone-strengthening vitamin D in most land vertebrates, including humans (specifically, UVB). [3] The UV spectrum thus has effects both beneficial and harmful to human health.

Sun tanning

Sun tanning or simply tanning is the process whereby skin color is darkened or tanned. It is most often a result of exposure to ultraviolet (UV) radiation from sunlight or from artificial sources, such as a tanning lamp found in indoor tanning beds. People who deliberately tan their skin by exposure to the sun engage in a passive recreational activity of sun bathing. Some people use chemical products which can produce a tanning effect without exposure to ultraviolet radiation, known as sunless tanning.

Sunburn burning of the skin by the suns radiation

Sunburn is a form of radiation burn that affects living tissue, such as skin, that results from an overexposure to ultraviolet (UV) radiation, commonly from the sun. Common symptoms in humans and other animals include red or reddish skin that is hot to the touch, pain, general fatigue, and mild dizziness. An excess of UV radiation can be life-threatening in extreme cases. Excessive UV radiation is the leading cause of primarily non-malignant skin tumors.

Skin cancer class of skin illnesses, tumor or cancer of the skin

Skin cancers are cancers that arise from the skin. They are due to the development of abnormal cells that have the ability to invade or spread to other parts of the body. There are three main types of skin cancers: basal-cell skin cancer (BCC), squamous-cell skin cancer (SCC) and melanoma. The first two, along with a number of less common skin cancers, are known as nonmelanoma skin cancer (NMSC). Basal-cell cancer grows slowly and can damage the tissue around it but is unlikely to spread to distant areas or result in death. It often appears as a painless raised area of skin, that may be shiny with small blood vessels running over it or may present as a raised area with an ulcer. Squamous-cell skin cancer is more likely to spread. It usually presents as a hard lump with a scaly top but may also form an ulcer. Melanomas are the most aggressive. Signs include a mole that has changed in size, shape, color, has irregular edges, has more than one color, is itchy or bleeds.

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

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. [4] Humans 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. [5] Under some conditions, children and young adults can see ultraviolet down to wavelengths of about 310 nm. [6] [7] Near-UV radiation is visible to insects, some mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays; this gives birds "true" UV vision. [8] [9]

Lens (anatomy) transparent structure of eye

The lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina. This adjustment of the lens is known as accommodation. Accommodation is similar to the focusing of a photographic camera via movement of its lenses. The lens is more flat on its anterior side than on its posterior side.

Cornea part of the eye

The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. The cornea, with the anterior chamber and lens, refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. The cornea can be reshaped by surgical procedures such as LASIK.

Photoreceptor cell specialized type of cell found in the retina that is capable of visual phototransduction

A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light into signals that can stimulate biological processes. To be more specific, photoreceptor proteins in the cell absorb photons, triggering a change in the cell's membrane potential.

Discovery

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

Latin Indo-European language of the Italic family

Latin is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets, and ultimately from the Phoenician alphabet.

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 "oxidizing rays" to emphasize chemical reactivity and to distinguish them from "heat rays", discovered the previous year at the other end of the visible spectrum. The simpler term "chemical rays" was adopted soon afterwards, and remained popular throughout the 19th century, although some said that this radiation was entirely different from light (notably John William Draper, who named them "tithonic rays" [10] [11] ). The terms "chemical rays" and "heat rays" were eventually dropped in favor of ultraviolet and infrared radiation, respectively. [12] [13] In 1878 the sterilizing effect of short-wavelength light by killing bacteria was discovered. By 1903 it was known the most effective wavelengths were around 250 nm. In 1960, the effect of ultraviolet radiation on DNA was established. [14]

Johann Wilhelm Ritter German physicist

Johann Wilhelm Ritter was a German chemist, physicist and philosopher. He was born in Samitz (Zamienice) near Haynau (Chojnów) in Silesia, and died in Munich.

Silver chloride chemical compound

Silver chloride is a chemical compound with the chemical formula AgCl. This white crystalline solid is well known for its low solubility in water (this behavior being reminiscent of the chlorides of Tl+ and Pb2+). Upon illumination or heating, silver chloride converts to silver (and chlorine), which is signaled by grey to black or purplish coloration to some samples. AgCl occurs naturally as a mineral chlorargyrite.

In chemistry, reactivity is the impetus for which a chemical substance undergoes a chemical reaction, either by itself or with other materials, with an overall release of energy.

The discovery of the ultraviolet radiation with wavelengths below 200 nm, named "vacuum ultraviolet" because it is strongly absorbed by the oxygen in air, was made in 1893 by the German physicist Victor Schumann. [15]

Victor Schumann German spectroscopist

Victor Schumann was a physicist and spectroscopist who in 1893 discovered the vacuum ultraviolet.

Subtypes

The electromagnetic spectrum of ultraviolet radiation (UVR), defined most broadly as 10–400 nanometers, can be subdivided into a number of ranges recommended by the ISO standard ISO-21348: [16]

NameAbbreviation Wavelength
(nm)
Photon energy
(eV, aJ)
Notes/alternative names
Ultraviolet AUVA315–4003.10–3.94
(0.497–0.631)
Long-wave, black light, not absorbed by the ozone layer: soft UV
Ultraviolet BUVB280–3153.94–4.43
(0.631–0.710)
Medium-wave, mostly absorbed by the ozone layer: intermediate UV
Ultraviolet CUVC100–2804.43–12.4
(0.710–1.987)
Short-wave, germicidal, completely absorbed by the ozone layer and atmosphere: hard UV
Near ultravioletNUV300–4003.10–4.13
(0.497–0.662)
Middle ultravioletMUV200–3004.13–6.20
(0.662–0.993)
Far ultravioletFUV122–2006.20–10.16
(0.993–1.628)
Hydrogen
Lyman-alpha
H Lyman-α121–12210.16–10.25
(1.628–1.642)
Spectral line at 121.6 nm, 10.20 eV.
Ionizing radiation at shorter wavelengths
Vacuum ultravioletVUV10–2006.20–124
(0.993–19.867)
Strongly absorbed by atmospheric oxygen,
though 150–200 nm wavelengths can propagate through nitrogen
Extreme ultraviolet EUV10–12110.25–124
(1.642–19.867)
Entirely ionizing radiation by some definitions;
completely absorbed by the atmosphere

A variety of solid-state and vacuum devices have been explored for use in different parts of the UV spectrum. Many approaches seek to adapt visible light-sensing devices, but these can suffer from unwanted response to visible light and various instabilities. Ultraviolet can be detected by suitable photodiodes and photocathodes, which can be tailored to be sensitive to different parts of the UV spectrum. Sensitive ultraviolet photomultipliers are available. Spectrometers and radiometers are made for measurement of UV radiation. Silicon detectors are used across the spectrum. [17]

Vacuum UV, or VUV, wavelengths (shorter than 200 nm) are strongly absorbed by molecular oxygen in the air, though the longer wavelengths of about 150–200 nm can propagate through nitrogen. Scientific instruments can therefore utilize this spectral range by operating in an oxygen-free atmosphere (commonly pure nitrogen), without the need for costly vacuum chambers. Significant examples include 193 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 can be used to remove unwanted visible light that contaminates the VUV, in general, detectors can be limited by their response to non-VUV radiation, and the development of "solar-blind" devices has been an important area of research. Wide-gap solid-state devices or vacuum devices with high-cutoff photocathodes can be attractive compared 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 materials, but it is possible to synthesize multilayer optics that reflect up to about 50 percent of EUV radiation at normal incidence. This technology was pioneered by the NIXT and MSSTA sounding rockets in the 1990s, and it has been used to make telescopes for solar imaging. See also the Extreme Ultraviolet Explorer (EUVE) 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 of the circa 25 percent of the Sun's total UV light that penetrates the Earth's atmosphere. Ozone altitude UV graph.svg
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 of the circa 25 percent of the Sun's total UV light that penetrates the Earth's atmosphere.

Some sources use the distinction of "hard UV" and "soft UV" - in the case of astrophysics the boundary may be at the Lyman limit i.e. wavelength 91.2 nm, with "hard UV" being more energetic. [18] The same terms may also used in other fields, such as cosmetology, optoelectronic, etc. - the numerical value of the boundary between hard/soft even within similar scientific fields do not necessarily coincide; for example one applied physics publication used a boundary of 190 nm between hard and soft UV regions. [19]

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 space at 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. [20]

However, at ground level sunlight is 44% visible light, 3% ultraviolet (with the Sun at its zenith), and the remainder infrared. [21] [22] Thus, the atmosphere blocks about 77% of the Sun's UV, almost entirely in the shorter UV wavelengths, when the Sun is highest in the sky (zenith). Of the ultraviolet radiation that reaches the Earth's surface, more than 95% is the longer wavelengths of UVA, with the small remainder UVB. There is essentially no UVC. [23] The fraction of UVB which remains in UV radiation after passing through the atmosphere is heavily dependent on cloud cover and atmospheric conditions. Thick clouds may block up to 90% of UVB radiation, [24] but in "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 way as the visible blue light from those parts of the sky. UV-B also plays a major role in plant development as it affects most of the plant hormones. [25]

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 important in blocking most UVB and the remaining part of UVC not already blocked by ordinary oxygen in air.

Blockers and absorbers

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

In sunscreen, ingredients that absorb UVA/UVB rays, such as avobenzone, oxybenzone [26] 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 SPF (Sun Protection Factor) ratings for sunscreen. Standard summer fabrics have UPF of approximately 6, which means that about 20% of UV will pass through.

Suspended nanoparticles in stained glass prevent UV rays from causing chemical reactions that change image colors. A set of stained glass color reference chips is planned to be used to calibrate the color cameras for the 2019 ESA Mars rover mission, since they will remain unfaded by the high level of UV present at the surface of Mars. [27]

Common soda–lime glass is partially transparent to UVA but is opaque to shorter wavelengths, whereas fused quartz glass, depending on quality, can be transparent even to vacuum UV wavelengths. Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm. [28] [29] [30]

Wood's glass is a nickel-bearing form of glass with a deep blue-purple color that blocks most visible light and passes ultraviolet.

Artificial sources

"Black lights"

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

A black light lamp emits long-wave UVA radiation and little visible light. Fluorescent black light lamps work similarly to other fluorescent lamps, but use a phosphor on the inner tube surface which emits UVA radiation instead of visible light. Some lamps use a deep-bluish-purple Wood's glass optical filter that blocks almost all visible light with wavelengths longer than 400 nanometres. [31] Others use plain 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 fraction 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 used for theatrical and concert displays. Black lights are used in applications 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. UVA/UVB emitting bulbs are also sold for other special purposes, such as tanning lamps and reptile-keeping.

Short-wave ultraviolet lamps

Germicidal Lamp 1.jpg
9-watt germicidal UV lamp, in compact fluorescent (CF) form factor
Kvartsevaia lampa.JPG
Commercial germicidal lamp in butcher shop

Shortwave UV lamps are made using a fluorescent lamp tube with no phosphor coating, composed of fused quartz, since ordinary glass absorbs UVC. These lamps emit ultraviolet light with two peaks in the UVC 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 UVC 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 used extensively for disinfection of surfaces in laboratories and food-processing industries, and for disinfecting water supplies.

Incandescent lamps

'Black light' incandescent lamps are also made, from an incandescent light bulb with a filter coating which absorbs most visible light. Halogen lamps with fused quartz envelopes are used 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 used as stable sources, either windowless or with various windows such as magnesium fluoride. [32] 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 used 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 use in 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 nanometre UV LED makes some common household items fluoresce. UV LED Fluoresence.jpg
A 380 nanometre UV LED makes some common household items fluoresce.

Light-emitting diodes (LEDs) can be manufactured to emit radiation in the ultraviolet range. LED efficiency at 365 nm is about 5–8%, whereas efficiency at 395 nm is closer to 20%, and power outputs at these longer UV wavelengths are also better. Such LED arrays are beginning to be used for UV curing applications, and are already successful in digital print applications and inert UV curing environments. Power densities approaching 3 W/cm2 (30 kW/m2) are now possible, and this, coupled with recent developments by photoinitiator and resin formulators, makes the expansion of LED-cured UV materials likely.

UVC LEDs are beginning to be used in disinfection [33] and as line sources to replace deuterium lamps in liquid chromatography instruments. [34]

Ultraviolet lasers

Gas lasers, laser diodes and solid-state lasers can be manufactured to emit ultraviolet rays, and lasers are available which cover the entire UV range. The nitrogen gas laser uses electronic excitation of nitrogen molecules to emit a beam that is mostly UV. The strongest ultraviolet lines are at 337.1 nm and 357.6.6 nm, wavelength. Another type of high power gas laser is the excimer laser. They are widely used lasers emitting in ultraviolet and vacuum ultraviolet wavelength ranges. Presently, UV argon-fluoride (ArF) excimer lasers operating at 193 nm are routinely used in integrated circuit production by photolithography. The current wavelength limit of production of coherent UV is about 126 nm, characteristic of the Ar2* excimer laser.

Direct UV-emitting laser diodes are available at 375 nm. [35] UV diode lasers have been demonstrated using Ce:LiSAF crystals (cerium-doped lithium strontium aluminum fluoride), a process developed in the 1990s at Lawrence Livermore National Laboratory. [36] Wavelengths shorter than 325 nm are commercially generated in diode-pumped solid-state lasers. Ultraviolet lasers can also be made by applying frequency conversion to lower-frequency lasers.

Ultraviolet lasers have applications 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) via sum and difference frequency mixing

The vacuum ultraviolet (VUV) band (100–200 nm) can be 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-photon resonant near 193 nm) [37] or metal vapors (e.g. magnesium). By making one of the lasers tunable, the VUV can be tuned. If one of the lasers is resonant with a transition in the gas or vapor then the VUV production is intensified. However, resonances also generate wavelength dispersion, and thus the phase matching can limit the tunable range of the 4 wave mixing. Difference frequency mixing (lambda1 + lambda2 − lambda3) has an advantage over sum frequency mixing because the phase matching can provide greater tuning. [37] 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 VUV covering from 100 nm to 200 nm. [37] Practically, the lack of suitable gas/vapor cell window materials above the lithium fluoride cut-off wavelength limit the tuning range to longer than about 110 nm. Tunable VUV wavelengths down to 75 nm was achieved using window-free configurations. [38]

Plasma and synchrotron sources of extreme UV

Lasers have been used to indirectly generate non-coherent extreme UV (EUV) radiation at 13.5 nm for extreme ultraviolet lithography. The EUV 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. [39] This technique does not require a synchrotron, yet can produce UV at the edge of the X-ray spectrum. Synchrotron light sources can also produce all wavelengths of UV, including those at the boundary of the UV and X-ray spectra at 10 nm.

The impact of ultraviolet radiation on human health has implications for the risks and benefits of sun exposure and is also implicated in issues such as fluorescent lamps and health. Getting too much sun exposure can be harmful, but in moderation, sun exposure is beneficial. [40]

Beneficial effects

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

— World Health Organization [41]

UV light causes the body to produce vitamin D (specifically, UVB), which is essential for life. The human body needs some UV radiation in order for one to maintain adequate vitamin D levels; however, excess exposure produces harmful effects that typically outweigh the benefits. [41]

Vitamin D promotes the creation of serotonin. The production of serotonin is in direct proportion to the degree of bright sunlight the body receives. [42] Serotonin is thought to provide sensations of happiness, well being and serenity to human beings. [43]

Skin conditions

UV rays also treat certain skin conditions. Modern phototherapy has been used to successfully treat psoriasis, eczema, jaundice, vitiligo, atopic dermatitis, and localized scleroderma. [44] [45] In addition, UV light, in particular UVB radiation, has been shown to induce cell cycle arrest in keratinocytes, the most common type of skin cell. [46] As such, sunlight therapy can be a candidate for treatment of conditions such as psoriasis and exfoliative cheilitis, conditions in which skin cells divide more rapidly than usual or necessary. [47]

Harmful effects

In humans, excessive exposure to UV radiation can result in acute and chronic harmful effects on the eye's dioptric system and retina. The risk is elevated at high altitudes and people living in high latitude countries where snow covers the ground right into early summer and sun positions even at zenith are low, are particularly at risk. [48] Skin, the circadian and immune systems can also be affected. [49]

Ultraviolet photons harm the DNA molecules of living organisms in different ways. In one common damage event, adjacent thymine bases bond with each other, instead of across the "ladder". This "thymine dimer" makes a bulge, and the distorted DNA molecule does not function properly. DNA UV mutation.svg
Ultraviolet photons harm the DNA molecules of living organisms in different ways. In one common damage event, adjacent thymine bases bond with each other, instead of across the "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 is increased by almost a factor of 100 between the near UVB wavelengths of 315-295 nm Erythemal action spectrum.svg
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 is increased by almost a factor of 100 between the near UVB wavelengths of 315–295 nm

The differential effects of various wavelengths of light on the human cornea and skin are sometimes called the "erythemal action spectrum.". [50] The action spectrum shows that UVA does not cause immediate reaction, but rather UV begins to cause photokeratitis and skin redness (with Caucasians 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 UVC band. At still shorter wavelengths of UV, damage continues to happen, but the overt effects are not as great with 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 effects at a given time and location. This standard shows that most sunburn happens due to UV at wavelengths near the boundary of the UVA and UVB bands.

Skin damage

Overexposure to UVB radiation not only can cause sunburn but also some forms of skin cancer. However, the degree of redness and eye irritation (which are largely not caused by UVA) do not predict the long-term effects of UV, although they do mirror the direct damage of DNA by ultraviolet. [51]

All bands of UV radiation damage collagen fibers and accelerate aging of the skin. Both UVA and UVB destroy vitamin A in skin, which may cause further damage. [52]

UVB radiation can cause direct DNA damage. [53] 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 UVA radiation. This can be seen from the absence of a direct UV signature mutation in 92% of all melanoma. [54] Occasional overexposure and sunburn are probably greater risk factors for melanoma than long-term moderate exposure. [55] UVC is the highest-energy, most-dangerous type of ultraviolet radiation, and causes adverse effects that can variously be mutagenic or carcinogenic. [56]

In the past, UVA was considered not harmful or less harmful than UVB, but today it is known to contribute to skin cancer via indirect DNA damage (free radicals such as reactive oxygen species). UVA can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which in turn can damage DNA. The DNA damage caused indirectly to skin by UVA consists mostly of single-strand breaks in DNA, while the damage caused by UVB includes direct formation of thymine dimers or other pyrimidine dimers and double-strand DNA breakage. [57] UVA is immunosuppressive for the entire body (accounting for a large part of the immunosuppressive effects of sunlight exposure), and is mutagenic for basal cell keratinocytes in skin. [58]

UVB photons can cause direct DNA damage. UVB 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. [53] Those pyrimidine dimers that escape this repair process can induce a form of programmed cell death (apoptosis) or can cause DNA replication errors leading to mutation.

As a defense against UV radiation, the amount of the brown pigment melanin in the skin increases when exposed to moderate (depending on skin type) levels of radiation; this is commonly known as a sun tan. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, protecting the skin against both direct and indirect DNA damage from the UV. UVA gives a quick tan that lasts for days by oxidizing melanin that was already present and triggers the release of the melanin from melanocytes. UVB yields a tan that takes roughly 2 days to develop because it stimulates the body to produce more melanin.

Sunscreen safety debate
Demonstration of the effect of sunscreen. The man's face has sunscreen on his right only. The left image is a regular photograph of the face; the right image is taken by reflected UV light. The side of the face with sunscreen is darker because the sunscreen absorbs the UV light. UV and Vis Sunscreen.jpg
Demonstration of the effect of sunscreen. The man's face has sunscreen on his right only. The left image is a regular photograph of the face; the right image is taken by reflected UV light. The side of the face with sunscreen is darker because the sunscreen absorbs the UV light.

Medical organizations recommend that patients protect themselves from UV radiation by using sunscreen. Five sunscreen ingredients have been shown to protect mice against skin tumors. However, some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells. [59] [60] The amount of sunscreen that penetrates into the lower layers of the skin may be large enough to cause damage. [61]

Sunscreen reduces the direct DNA damage that causes sunburn, by blocking UVB, and the usual SPF rating indicates how effectively this radiation is blocked. SPF is, therefore, also called UVB-PF, for "UVB protection factor". [62] This rating, however, offers no data about important protection against UVA, [63] which does not primarily cause sunburn but is still harmful, since it causes indirect DNA damage and is also considered carcinogenic. Several studies suggest that the absence of UVA filters may be the cause of the higher incidence of melanoma found in sunscreen users compared to non-users. [64] [65] [66] [67] [68] Some sunscreen lotions now contain compounds including titanium dioxide, zinc oxide and avobenzone which helps protect against UVA 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. [69] [59] [60] [70] The amount of sunscreen that penetrates through the stratum corneum may or may not be large enough 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 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. [69] 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. [69]

Aggravation of certain skin conditions

Ultraviolet radiation can aggravate several skin conditions and diseases, including [71] systemic lupus erythematosus, Sjögren's syndrome, Sinear Usher syndrome, rosacea, dermatomyositis, Darier's disease, and Kindler–Weary syndrome.

Eye damage

Signs are often used to warn of the hazard of strong UV sources. UV Warning.jpg
Signs are often used to warn of the hazard of strong UV sources.

The eye is most sensitive to damage by UV in the lower UVC 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 can cause "welder's flash" or "arc eye" (photokeratitis) and can lead to cataracts, pterygium and pinguecula formation. To a lesser extent, UVB in sunlight from 310–280 nm also causes photokeratitis ("snow blindness"), and the cornea, the lens, and the retina can be damaged. [72]

Protective eyewear is beneficial to those exposed to ultraviolet radiation. Since light can reach 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. [73] [74] Ordinary, untreated eyeglasses give some protection. Most plastic lenses give more protection than glass lenses, because, as noted above, glass is transparent to UVA and the common acrylic plastic used for lenses is less so. Some plastic lens materials, such as polycarbonate, inherently block most UV. [75]

Degradation of polymers, pigments and dyes

UV damaged polypropylene rope (left) and new rope (right) Failedrope1.jpg
UV damaged polypropylene rope (left) and new rope (right)

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

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.

IR spectrum showing carbonyl absorption due to UV degradation of polyethylene Irspec2.jpg
IR spectrum showing carbonyl absorption due to UV degradation of polyethylene

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

Applications

Because of its ability to cause chemical reactions and excite fluorescence in materials, ultraviolet radiation has a number of applications. The following table [76] gives some uses of specific wavelength bands in the UV spectrum

Photography

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

Photographic film responds to ultraviolet radiation but the glass lenses of cameras usually block radiation shorter than 350 nm. Slightly yellow UV-blocking filters are often used for outdoor photography to prevent unwanted bluing and overexposure by UV rays. For photography in the near UV, special filters may be used. 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 can be removed, or they may be absent, and an external visible-light filter prepares the camera for near-UV photography. A few cameras are designed for use in the UV.

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

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

In ultraviolet astronomy, measurements are used 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 made from space.

Electrical and electronics industry

Corona discharge on electrical apparatus can be detected by its ultraviolet emissions. Corona causes degradation of electrical insulation and emission of ozone and nitrogen oxide. [78]

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 allows the UV radiation in.

Fluorescent dye uses

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 present and causes the colors and whites to appear whiter or more brightly colored.

UV fluorescent dyes that glow in the primary colors are used in paints, papers, and textiles either to enhance color under daylight illumination or to provide special effects when lit with UV lamps. Blacklight paints that contain dyes that glow under UV are used in a number of art and aesthetic applications.

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

To help prevent counterfeiting of currency, or forgery of important documents such as driver's licenses and passports, the paper may include a 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 used in many applications (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 help police identify the attacker later. [79]

In some types of nondestructive testing UV stimulates fluorescent dyes to highlight defects in a broad range of materials. These dyes may be carried into surface-breaking defects by capillary action (liquid penetrant inspection) or they may be bound to ferrite particles caught in magnetic leakage fields in ferrous materials (magnetic particle inspection).

Analytic uses

Forensics

UV is an investigative tool at the crime scene helpful in locating and identifying bodily fluids such as semen, blood, and saliva. [80] For example, ejaculated fluids or saliva can be detected by high-power UV sources, irrespective of the structure or colour of the surface the fluid is deposited upon. [81] UV-Vis microspectroscopy is also used to analyze trace evidence, such as textile fibers and paint chips, as well as questioned documents.

Other applications include the authentication of various collectibles and art, and detecting counterfeit currency. Even materials not specially marked with UV sensitive dyes may have distinctive fluorescence under UV exposure or may fluoresce differently under short-wave versus long-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 can be found for distinguishing ink from paper on the papyrus surface.

Simple NUV sources can be used to highlight faded iron-based ink on vellum. [82]

Sanitary compliance

After a training exercise involving fake body fluids, a healthcare worker's personal protective equipment is checked with ultraviolet light to find invisible drops of fluids. These fluids could contain deadly viruses or other contamination. Ultra-violet screening for potentially Ebola-carrying liquids (15811190376).jpg
After a training exercise involving fake body fluids, a healthcare worker's personal protective equipment is checked with ultraviolet light to find invisible drops of fluids. These fluids could contain deadly viruses or other contamination.

Ultraviolet aids in the detection of organic material deposits that remain on surfaces where periodic cleaning and sanitizing may not have been properly accomplished. It is used in the hotel industry, manufacturing, and other industries where levels of cleanliness or contamination are inspected. [83] [84] [85] [86]

Perennial news feature for many television news organizations involves an investigative reporter's using a similar device to reveal unsanitary conditions in hotels, public toilets, hand rails, and such. [87] [88]

Chemistry

UV/VIS spectroscopy is widely used as a technique in chemistry to analyze chemical structure, the most notable one being conjugated systems. UV radiation is often used to excite a given sample where the fluorescent emission is measured with a spectrofluorometer. In biological research, UV radiation is used for quantification of nucleic acids or proteins.

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

Ultraviolet lamps are also used in analyzing minerals and gems.

In pollution control applications, ultraviolet analyzers are used to detect emissions of nitrogen oxides, sulfur compounds, mercury, and ammonia, for example in the flue gas of fossil-fired power plants. [89] Ultraviolet radiation can detect thin sheens of spilled oil on water, either by the high reflectivity of oil films at UV wavelengths, fluorescence of compounds in oil or by absorbing of UV created by Raman scattering in water. [90]

Material science uses

Fire detection

In general, ultraviolet detectors 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. 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 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. Arc welding, electrical arcs, lightning, X-rays used in nondestructive metal testing equipment (though this is highly unlikely), and radioactive materials can produce levels that will activate a UV detection system. The presence of UV-absorbing gases and vapors will attenuate the UV radiation from a fire, adversely affecting the ability of the detector to detect flames. Likewise, the presence of an oil mist in the air or an oil film on the detector window will have the same effect.

Photolithography

Ultraviolet radiation is used for very fine resolution photolithography, a procedure wherein a chemical called a photoresist is exposed to UV radiation that has passed through a mask. 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 modify areas of the sample where no photoresist remains.

Photolithography is used in the manufacture of semiconductors, integrated circuit components, [91] and printed circuit boards. Photolithography processes used to fabricate electronic integrated circuits presently use 193 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) can be potted using acrylic resins that are cured using UV energy. The advantages are low VOC emissions and rapid curing.

Effects of UV on finished surfaces in 0, 20 and 43 hours. UV effect on finished wood.jpg
Effects 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. Applications include glass 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 applications include UV lamps, UV LEDs, and Excimer flash lamps. Fast processes such as flexo or offset printing require high-intensity light focused via reflectors onto a moving substrate and medium so high-pressure Hg (mercury) or Fe (iron, doped)-based bulbs are used, energized with electric arcs or microwaves. Lower-power fluorescent lamps and LEDs can be used for static applications. Small high-pressure lamps can have light focused and transmitted to the work area via liquid-filled or fiber-optic light guides.

The impact of UV on polymers is used for modification of the (roughness and hydrophobicity) of polymer surfaces. For example, a poly(methyl methacrylate) surface can be smoothed by vacuum ultraviolet. [92]

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.

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 can hinder the resulting reaction creating formadehyde, aldehyde, and other VOC's en route to a final stage. Thus, the use of 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 can destroy DNA in living microorganisms. [93] UVC's effectiveness is directly related to intensity and exposure time.

UV has also been shown to reduce gaseous contaminants such as carbon monoxide and VOCs. [94] [95] [96] UV lamps radiating at 184 and 254 nm can remove 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. UV-ontsmetting laminaire-vloeikast.JPG
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 used to sterilize workspaces and tools used in biology laboratories and medical facilities. Commercially available low-pressure mercury-vapor lamps emit about 86% of their radiation at 254 nanometers (nm), with 265 nm being the peak germicidal effectiveness curve. UV at these germicidal wavelengths damage a microorganism's DNA so that it cannot reproduce, making it harmless, (even though the organism may not be killed). Since microorganisms can be shielded from ultraviolet rays in small cracks and other shaded areas, these lamps are used only as a supplement to other sterilization techniques.

UV-C LEDs are relatively new to the commercial market and are gaining in popularity. [97] Due to their monochromatic nature (± 5 nm) these LEDs can target a specific wavelength needed for disinfection. This is especially important knowing that pathogens vary in their sensitivity to specific UV wavelengths. LEDs are mercury free, instant on/off, and have unlimited cycling throughout the day. [98]

Disinfection using UV radiation is commonly used in wastewater treatment applications and is finding an increased usage in municipal drinking water treatment. Many bottlers of spring water use UV disinfection equipment to sterilize their water. Solar water disinfection [99] has been researched for cheaply treating contaminated water using natural sunlight. The UV-A irradiation and increased water temperature kill organisms in the water.

Ultraviolet radiation is used in several food processes to kill unwanted microorganisms. UV can be used to pasteurize fruit juices by flowing the juice over a high-intensity ultraviolet source. [100] 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 can produce flashes several times per second. Disinfection robots use pulsed UV [101]

Biological

Some animals, including birds, reptiles, and insects such as bees, can see 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 can be detected by pest control technicians for proper treatment of infested dwellings.

Butterflies use ultraviolet 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 find mates, males are attracted to the ultraviolet-reflecting color of female hind wings. [102] In Pieris napi butterflies it was shown that females in northern Finland with less UV-radiation present in the environment possessed stronger UV signals to attract their males than those occurring further south. This suggested that 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. [103]

Many insects use the 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. Ultraviolet trap entomologist.jpg
Entomologist using a UV light for collecting beetles in Chaco, Paraguay.

The green fluorescent protein (GFP) is often used 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 related fields. UV-capable spectrophotometers are common in such laboratories.

Ultraviolet traps called bug zappers are used to eliminate various small flying 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 used 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 used 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 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. [104]

Herpetology

Reptiles need UVB for biosynthesis of vitamin D, and other metabolic processes. Specifically cholecalciferol (vitamin D3), which is needed to for basic cellular / neural functioning as well as the utilization calcium for bone and egg production. The UVA wavelength is also visible to many reptiles and might play a signifiant role in their ability survive in the wild as well as 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 available for many captive species to survive. Simple supplementation 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 place important functions in the animals health. Natural sunlight in the right levels is always going to be superior to artificial sources, but this might be possible for keepers in different parts of the world.

It is a known problem that high levels of output of the UVa part of the spectrum can both cause cellular and DNA damage to sensitive parts of their bodies - especially the eyes were blindness is the result from an improper UVa/b source use and 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 should be 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 can have their needs met. A better strategy is to use individual sources of these elements and so they can be placed and controlled by the keepers for the max benefit of the animals. [105]

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 material and 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 believed to be evolved modifications of the enzymes originally used to overcome DNA damages caused by UV. [106]

See also

Related Research Articles

Sunscreen topical skin product that helps protect against sunburn

Sunscreen, also known as sunblock, sun cream or suntan lotion, is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet (UV) radiation and thus helps protect against sunburn. Diligent use of sunscreen can also slow or temporarily prevent the development of wrinkles, moles and sagging skin.

Blacklight

A blacklight, also referred to as a UV-A light, Wood's lamp, or simply ultraviolet light, is a lamp that emits long-wave (UV-A) ultraviolet light and very little visible light.

Indoor tanning

Indoor tanning involves using a device that emits ultraviolet radiation to produce a cosmetic tan. Typically found in tanning salons, gyms, spas, hotels, and sporting facilities, and less often in private residences, the most common device is a horizontal tanning bed, also known as a sunbed or solarium. Vertical devices are known as tanning booths or stand-up sunbeds.

Light therapy—or phototherapy, classically referred to as heliotherapy—consists of exposure to daylight or to specific wavelengths of light using polychromatic polarised light, lasers, light-emitting diodes, fluorescent lamps, dichroic lamps or very bright, full-spectrum light. The light is administered for a prescribed amount of time and, in some cases, at a specific time of day.

Ultraviolet light therapy or ultraviolet phototherapy is a form of treatment for certain skin disorders including atopic skin disorder and vitiligo when used with psoralen to form the PUVA treatment. It consists of irradiation of the patient with the UVA band of ultraviolet light, usually delivered from a fluorescent bulb specially designed to output this frequency of ultraviolet.

The ultraviolet index or UV Index is an international standard measurement of the strength of sunburn-producing ultraviolet (UV) radiation at a particular place and time. The scale was developed by Canadian scientists in 1992, then adopted and standardized by the UN's World Health Organization and World Meteorological Organization in 1994. It is primarily used in daily forecasts aimed at the general public, and is increasingly available as an hourly forecast as well.

Ecamsule chemical compound

Ecamsule is an organic compound which is added to many sunscreens to filter out UVA rays. It is a benzylidene camphor derivative, many of which are known for their excellent photostability.

UV filter camera parts, features and technologies

UV filters are individual compounds or mixtures that block or absorb ultraviolet (UV) light. Two major applications of UV filters are in sunscreens, where they protect the skin from sunburn and other damage, and in photography, where they reduce the level of ultraviolet light that strikes the recording medium. When exposed to UV light, these filters can undergo transformations into other chemicals that are less protective and possibly toxic. As a result, there are practical concerns about the choice of chemical to use beyond just which has the desired filtering properties.

Octocrylene chemical compound

Octocrylene is an organic compound used as an ingredient in sunscreens and cosmetics. It is an ester formed by the reaction of 3,3-diphenylcyanoacrylate with 2-ethylhexanol. It is a viscous, oily liquid that is clear and colorless.

Photochromic lens

Photochromic lenses are optical lenses that darken on exposure to specific types of light of sufficient intensity, most commonly ultraviolet (UV) radiation. In the absence of activating light the lenses return to their clear state. Photochromic lenses may be made of glass, polycarbonate, or another plastic. They are principally used in eyeglasses that are dark in bright sunlight, but clear in low ambient light conditions. They darken significantly within about a minute of exposure to bright light, and take somewhat longer to clear. A range of clear and dark transmittances are available.

Ultraviolet photography is a photographic process of recording images by using light from the ultraviolet (UV) spectrum only. Images taken with ultraviolet light serve a number of scientific, medical or artistic purposes. Images may reveal deterioration of art works or structures not apparent under visible light. Diagnostic medial images may be used to detect certain skin disorders or as evidence of injury. Some animals, particularly insects, use ultraviolet wavelengths for vision; ultraviolet photography can help investigate the markings of plants that attract insects, while invisible to the unaided human eye. Ultraviolet photography of archaeological sites may reveal artifacts or traffic patterns not otherwise visible.

Artificial sunlight

Artificial sunlight is the use of a light source to simulate sunlight where the unique characteristics of sunlight are needed, but where sufficient natural sunlight is not available or is not feasible. A light source used to simulate sunlight is a solar simulator.

Ultraviolet germicidal irradiation Disinfection method that uses short-wavelength ultraviolet light to kill or inactivate microorganisms

Ultraviolet germicidal irradiation (UVGI) is a disinfection method that uses short-wavelength ultraviolet (UV-C) light to kill or inactivate microorganisms by destroying nucleic acids and disrupting their DNA, leaving them unable to perform vital cellular functions. UVGI is used in a variety of applications, such as food, air, and water purification.

UV-B lamps are lamps that emit a spectrum of ultraviolet light with wavelengths ranging from 290–320 nanometers. This spectrum is also commonly called the biological spectrum due to the human body's sensitivity to light of such a wavelength. UV-B light does not tan the skin very much, compared to the UV-A lamps that are used in tanning beds.

Photoaging or photoageing is a term used for the characteristic changes to skin induced by chronic UVA and UVB exposure. Tretinoin is the best studied retinoid in the treatment of photoaging

Health effects of sunlight exposure

The ultraviolet radiation in sunlight has both positive and negative health effects, as it is both a principal source of vitamin D3 and a mutagen. A dietary supplement can supply vitamin D without this mutagenic effect. Vitamin D has been suggested as having a wide range of positive health effects, which include strengthening bones and possibly inhibiting the growth of some cancers. UV exposure also has positive effects for endorphin levels, and possibly for protection against multiple sclerosis. Visible sunlight to the eyes gives health benefits through its association with the timing of melatonin synthesis, maintenance of normal and robust circadian rhythms, and reduced risk of seasonal affective disorder.

Non-ionizing radiation electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules

Non-ionizingradiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules—that is, to completely remove an electron from an atom or molecule. Instead of producing charged ions when passing through matter, non-ionizing electromagnetic radiation has sufficient energy only for excitation, the movement of an electron to a higher energy state. Ionizing radiation which has a higher frequency and shorter wavelength than nonionizing radiation, has many uses but can be a health hazard; exposure to it can cause burns, radiation sickness, cancer, and genetic damage. Using ionizing radiation requires elaborate radiological protection measures which in general are not required with nonionizing radiation.

References

  1. "Reference Solar Spectral Irradiance: Air Mass 1.5". Archived from the original on 27 January 2011. Retrieved 12 November 2009.
  2. Haigh, Joanna D. . (2007). "The Sun and the Earth's Climate: Absorption of solar spectral radiation by the atmosphere". Living Reviews in Solar Physics. 4 (2): 2. Bibcode:2007LRSP....4....2H. doi:10.12942/lrsp-2007-2. Archived from the original on 4 March 2016. Retrieved 12 July 2014.
  3. Wacker, Matthias; Holick, Michael F. (2013-01-01). "Sunlight and Vitamin D". Dermato-endocrinology. 5 (1): 51–108. doi:10.4161/derm.24494. ISSN   1938-1972. PMC   3897598 . PMID   24494042.
  4. M A Mainster (2006). "Violet and blue light blocking intraocular lenses: photoprotection versus photoreception". British Journal of Ophthalmology. 90 (6): 784–792. doi:10.1136/bjo.2005.086553. PMC   1860240 . PMID   16714268.
  5. David Hambling (29 May 2002). "Let the light shine in". The Guardian. Archived from the original on 23 November 2014. Retrieved 2 January 2015.
  6. Lynch, David K.; Livingston, William Charles (2001). Color and Light in Nature (2nd ed.). Cambridge, UK: Cambridge University Press. p. 231. ISBN   978-0-521-77504-5. Archived from the original on 31 December 2013. Retrieved 12 October 2013. Limits of the eye's overall range of sensitivity extends from about 310 to 1050 nanometers
  7. Dash, Madhab Chandra; Dash, Satya Prakash (2009). Fundamentals Of Ecology 3E. Tata McGraw-Hill Education. p. 213. ISBN   978-1-259-08109-5. Archived from the original on 31 December 2013. Retrieved 18 October 2013. Normally the human eye responds to light rays from 390 to 760 nm. This can be extended to a range of 310 to 1,050 nm under artificial conditions.
  8. Bennington-Castro, Joseph. "Want ultraviolet vision? You're going to need smaller eyes". Archived from the original on 7 May 2016.
  9. Hunt, D. M.; Carvalho, L. S.; Cowing, J. A.; Davies, W. L. (2009). "Evolution and spectral tuning of visual pigments in birds and mammals". Philosophical Transactions of the Royal Society B: Biological Sciences. 364 (1531): 2941–2955. doi:10.1098/rstb.2009.0044. ISSN   0962-8436. PMC   2781856 . PMID   19720655.
  10. "On a new Imponderable Substance and on a Class of Chemical Rays analogous to the rays of Dark Heat", J.W. Draper, The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 1842, LXXX, pp.453–461
  11. "Description of the Tithonometer", J.W. Draper, The Practical Mechanic and Engineer's Magazine, January 1844, pp.122–127
  12. Beeson, Steven; Mayer, James W (2007-10-23). "12.2.2 Discoveries beyond the visible". Patterns of light: chasing the spectrum from Aristotle to LEDs. New York: Springer. p. 149. ISBN   978-0-387-75107-8.
  13. Hockberger, Philip E. (2002). "A history of ultraviolet photobiology for humans, animals and microorganisms". Photochem. Photobiol. 76 (6): 561–79. doi:10.1562/0031-8655(2002)0760561AHOUPF2.0.CO2. PMID   12511035. (Subscription required (help)). Closed Access logo alternative.svg
  14. James Bolton, Christine Colton, The Ultraviolet Disinfection Handbook, American Water Works Association, 2008 ISBN   978 1 58321 584 5, pp. 3–4
  15. The ozone layer also protects living beings from this. Lyman, T. (1914). "Victor Schumann". Astrophysical Journal. 38: 1–4. Bibcode:1914ApJ....39....1L. doi:10.1086/142050.
  16. "ISO 21348 Definitions of Solar Irradiance Spectral Categories" (PDF). Archived (PDF) from the original on 29 October 2013.
  17. "Gullikson, Korde, Canfield, Vest, " Stable Silicon Photodiodes for absolute intensity measurements in the VU V and soft x-ray regions", Jrnl of Elec. Spect. and Related Phenomena 80(1996) 313–316" (PDF). Ts.nist.gov. Archived from the original (PDF) on 2009-01-09. Retrieved 2011-11-08.
  18. Bally, John; Reipurth, Bo (2006), The Birth of Stars and Planets, Cambridge University Press, p. 177
  19. "Slipping surface discharge as a source of hard UV radiation", Journal of Physics D: Applied Physics, 33 (7)
  20. "Solar radiation" (PDF). Archived (PDF) from the original on 1 November 2012.
  21. "Introduction to Solar Radiation". www.newport.com. Archived from the original on 29 October 2013.
  22. "Reference Solar Spectral Irradiance: Air Mass 1.5". Archived from the original on 28 September 2013. Retrieved 12 November 2009.
  23. Understanding UVA and UVB, archived from the original on 1 May 2012, retrieved 30 April 2012
  24. "What does SPF Mean?"
  25. Hormone-controlled UV-B responses in plants, archived from the original on 8 July 2016
  26. Burnett, M. E.; Wang, S. Q. (2011). "Current sunscreen controversies: a critical review". Photodermatology, Photoimmunology & Photomedicine. 27 (2): 58–67. doi:10.1111/j.1600-0781.2011.00557.x. PMID   21392107.
  27. ELLIE ZOLFAGHARIFARD (15 October 2013). "How medieval stained-glass is creating the ultimate SPACE camera: Nanoparticles used in church windows will help scientists see Mars' true colours under extreme UV light". Archived from the original on 28 December 2013.
  28. "Soda Lime Glass Transmission Curve". Archived from the original on 27 March 2012.
  29. "B270-Superwite Glass Transmission Curve". Präzisions Glas & Optik. Archived from the original on 9 July 2017. Retrieved 13 January 2017.
  30. "Selected Float Glass Transmission Curve". Präzisions Glas & Optik. Archived from the original on 19 October 2015. Retrieved 13 January 2017.
  31. "Insect-O-Cutor" (PDF). Archived (PDF) from the original on 4 June 2013.
  32. Klose, Jules Z.; Bridges, J. Mervin; Ott, William R. (June 1987). "NBS Measurement Services: Radiometric Standards in the VUV" (PDF). NBS Special Publication (250–3). Archived (PDF) from the original on 11 June 2016.
  33. Boyce, JM (2016). "Modern technologies for improving cleaning and disinfection of environmental surfaces in hospitals". Antimicrobial Resistance and Infection Control. 5: 10. doi:10.1186/s13756-016-0111-x. PMC   4827199 . PMID   27069623.
  34. "UVC LEDs Enhance Chromatography Applications - GEN". GEN. Archived from the original on 4 November 2016.
  35. "UV Laser Diode: 375 nm Center Wavelength". Product Catalog. United States: Thorlabs. Retrieved 14 December 2014.
  36. Marshall, Chris (1996). "A simple, reliable ultraviolet laser: the Ce:LiSAF". Lawrence Livermore National Laboratory. Archived from the original on 20 September 2008. Retrieved 11 January 2008.
  37. 1 2 3 Strauss, CEM; Funk, DJ (1991). "Broadly tunable difference-frequency generation of VUV using two-photon resonances in H2 and Kr". Optics Letters. 16 (15): 1192. Bibcode:1991OptL...16.1192S. doi:10.1364/ol.16.001192.
  38. Xiong, Bo; Chang, Yih-Chung; Ng, Cheuk-Yiu (2017). "Quantum-state-selected integral cross sections for the charge transfer collision of O2+(a4Πu5/2,3/2,1/2,−1/2: v+=1–2; J+) [O2+(X2Πg3/2,1/2: v+=22–23; J+)] + Ar at center-of-mass collision energies of 0.05–10.00 eV". Phys. Chem. Chem. Phys. 19 (43): 29057–29067. Bibcode:2017PCCP...1929057X. doi:10.1039/C7CP04886F. PMID   28920600. Archived from the original on 15 November 2017.
  39. "EUV Nudges Toward 10nm - EE Times". EETimes. Archived from the original on 15 October 2014.
  40. Sivamani, RK; Crane, LA; Dellavalle, RP (April 2009). "The benefits and risks of ultraviolet tanning and its alternatives: the role of prudent sun exposure". Dermatologic Clinics. 27 (2): 149–54, vi. doi:10.1016/j.det.2008.11.008. PMC   2692214 . PMID   19254658.
  41. 1 2 "The known health effects of UV, Ultraviolet radiation and the INTERSUN Programme" Archived 16 October 2016 at the Wayback Machine , World Health Organization.
  42. Korb, Alex, "Boosting Your Serotonin Activity" Archived 1 August 2017 at Archive.today . Psychology Today, 17 November 2011.
  43. Young, S. N. (2007). "How to increase serotonin in the human brain without drugs". Journal of Psychiatry and Neuroscience. 32 (6): 394–399. PMC   2077351 . PMID   18043762.
  44. Juzeniene, Asta; Moan, Johan (27 October 2014). "Beneficial effects of UV radiation other than via vitamin D production". Dermato-Endocrinology. 4 (2): 109–117. doi:10.4161/derm.20013. PMC   3427189 . PMID   22928066.
  45. "Health effects of ultraviolet radiation" Archived 8 October 2016 at the Wayback Machine . Government of Canada.
  46. Herzinger, T; Funk, J. O; Hillmer, K; Eick, D; Wolf, D. A; Kind, P (1995). "Ultraviolet B irradiation-induced G2 cell cycle arrest in human keratinocytes by inhibitory phosphorylation of the cdc2 cell cycle kinase". Oncogene. 11 (10): 2151–6. PMID   7478536.
  47. Bhatia, Bhavnit K.; Bahr, Brooks A.; Murase, Jenny E. (2015). "Excimer laser therapy and narrowband ultraviolet B therapy for exfoliative cheilitis". International Journal of Women's Dermatology. 1 (2): 95–98. doi:10.1016/j.ijwd.2015.01.006. PMC   5418752 . PMID   28491966.
  48. Meyer-Rochow, Victor Benno (2000). "Risks, especially for the eye, emanating from the rise of solar UV-radiation in the Arctic and Antarctic regions". International Journal of Circumpolar Health. 59 (1): 38–51. PMID   10850006.
  49. "Health effects of UV radiation". World Health Organization. Archived from the original on 17 March 2015.
  50. "Navy Ultraviolet Radiation Guide" (PDF). Archived (PDF) from the original on 17 June 2015.
  51. "What Is Ultraviolet (UV) Radiation?". www.cancer.org. Archived from the original on 3 April 2017. Retrieved 11 June 2017.
  52. Torma, H; Berne, B; Vahlquist, A (1988). "UV irradiation and topical vitamin A modulate retinol esterification in hairless mouse epidermis". Acta Derm. Venereol. 68 (4): 291–299. PMID   2459873.
  53. 1 2 Bernstein C, Bernstein H, Payne CM, Garewal H (June 2002). "DNA repair/pro-apoptotic dual-role proteins in five major DNA repair pathways: fail-safe protection against carcinogenesis". Mutat. Res. 511 (2): 145–78. doi:10.1016/S1383-5742(02)00009-1. PMID   12052432.
  54. Davies H.; Bignell G. R.; Cox C. (June 2002). "Mutations of the BRAF gene in human cancer". Nature. 417 (6892): 949–954. doi:10.1038/nature00766. PMID   12068308. Archived from the original on 5 March 2008.
  55. Richard Weller (10 June 2015). "Shunning the sun may be killing you in more ways than you think". New Scientist . Archived from the original on 9 June 2017.
  56. C.Michael Hogan. 2011. Sunlight. eds. P.Saundry & C.Cleveland. Encyclopedia of Earth. Archived 19 October 2013 at the Wayback Machine
  57. Svobodová AR, Galandáková A, Sianská J, et al. (January 2012). "DNA damage after acute exposure of mice skin to physiological doses of UVB and UVA light". Arch Dermatol Res. 304 (5): 407–412. doi:10.1007/s00403-012-1212-x. PMID   22271212.
  58. Halliday GM, Byrne SN, Damian DL (December 2011). "Ultraviolet A radiation: its role in immunosuppression and carcinogenesis". Semin Cutan Med Surg. 30 (4): 214–21. doi:10.1016/j.sder.2011.08.002. PMID   22123419.
  59. 1 2 Xu, C.; Green, Adele; Parisi, Alfio; Parsons, Peter G (2001). "Photosensitization of the Sunscreen Octyl p-Dimethylaminobenzoate b UVA in Human Melanocytes but not in Keratinocytes". Photochemistry and Photobiology. 73 (6): 600–604. doi:10.1562/0031-8655(2001)073<0600:POTSOP>2.0.CO;2. PMID   11421064.
  60. 1 2 Knowland, John; McKenzie, Edward A.; McHugh, Peter J.; Cridland, Nigel A. (1993). "Sunlight-induced mutagenicity of a common sunscreen ingredient". FEBS Letters. 324 (3): 309–313. doi:10.1016/0014-5793(93)80141-G. PMID   8405372.
  61. Chatelaine, E.; Gabard, B.; Surber, C. (2003) pdf Skin Penetration and Sun Protection Factor of Five UV Filters: Effect of the Vehicle Archived 27 December 2013 at the Wayback Machine , Skin Pharmacol. Appl. Skin Physiol., 16:28–35 doi : 10.1159/000068291 PMID   12566826
  62. Stephens TJ, Herndon JH, Colón LE, Gottschalk RW (February 2011). "The impact of natural sunlight exposure on the UVB-sun protection factor (UVB-SPF) and UVA protection factor (UVA-PF) of a UVA/UVB SPF 50 sunscreen". J Drugs Dermatol. 10 (2): 150–155. PMID   21283919.
  63. Couteau C, Couteau O, Alami-El Boury S, Coiffard LJ (August 2011). "Sunscreen products: what do they protect us from?". Int J Pharm. 415 (1–2): 181–4. doi:10.1016/j.ijpharm.2011.05.071. PMID   21669263.
  64. Garland C, Garland F, Gorham E (1992). "Could sunscreens increase melanoma risk?". Am J Public Health. 82 (4): 614–5. doi:10.2105/AJPH.82.4.614. PMC   1694089 . PMID   1546792.
  65. Westerdahl J, Ingvar C, Masback A, Olsson H (2000). "Sunscreen use and malignant melanoma". International Journal of Cancer. 87 (1): 145–150. doi:10.1002/1097-0215(20000701)87:1<145::AID-IJC22>3.0.CO;2-3. PMID   10861466.
  66. Autier P, Dore JF, Schifflers E, et al. (1995). "Melanoma and use of sunscreens: An EORTC case control study in Germany, Belgium and France". Int. J. Cancer. 61 (6): 749–755. doi:10.1002/ijc.2910610602. PMID   7790106.
  67. Weinstock, M. A. (1999). "Do sunscreens increase or decrease melanoma risk: An epidemiologic evaluation". Journal of Investigative Dermatology Symposium Proceedings. 4 (1): 97–100. doi:10.1038/sj.jidsp.5640190 (inactive 2018-09-06). PMID   10537017.
  68. Vainio, H.; Bianchini, F. (2000). "Cancer-preventive effects of sunscreens are uncertain". Scandinavian Journal of Work Environment and Health. 26: 529–531.
  69. 1 2 3 Hanson Kerry M.; Gratton Enrico; Bardeen Christopher J. (2006). "Sunscreen enhancement of UV-induced reactive oxygen species in the skin". Free Radical Biology and Medicine. 41 (8): 1205–1212. doi:10.1016/j.freeradbiomed.2006.06.011. PMID   17015167.
  70. Damiani, E.; Greci, L.; Parsons, R.; Knowland (1999). "Nitroxide radicals protect DNA from damage when illuminated in vitro in the presence of dibenzoylmethane and a common sunscreen ingredient". Free Radic. Biol. Med. 26 (7–8): 809–816. doi:10.1016/S0891-5849(98)00292-5.
  71. European Guidelines for Photodermatoses > 2 Photoaggravated Disorders [ dead link ] at European Dermatology Forum
  72. "The known health effects of UV". World Health Organization. Archived from the original on 24 October 2016.
  73. "UV radiation". World Health Organization. Archived from the original on 25 October 2016.
  74. "What is UV radiation and how much does it increase with altitude?". NOAA. Archived from the original on 3 January 2017.
  75. "Optical properties of lens materials - Optician". www.opticianonline.net. Archived from the original on 26 October 2016.
  76. "s-et.com". Archived from the original on 20 August 2008. Retrieved 26 September 2009.CS1 maint: BOT: original-url status unknown (link)
  77. "Ultraviolet Light, UV Rays, What is Ultraviolet, UV Light Bulbs, Fly Trap". Pestproducts.com. Archived from the original on 8 October 2011. Retrieved 8 November 2011.
  78. "Corona – The Daytime UV Inspection Magazine". Archived from the original on 1 August 2004.
  79. "Pepper Spray FAQ". Archived from the original on 15 June 2013.
  80. Springer, E; Almog, J; Frank, A; Ziv, Z; Bergman, P; Gui Quang, W (1994). "Detection of dry bodily fluids by inherent short wavelength UV luminescence: Preliminary results". Forensic Sci Int. 66 (2): 89–94. doi:10.1016/0379-0738(94)90332-8. PMID   8063277. Archived from the original on 2012-09-12. Retrieved 2012-02-14.
  81. Anja Fiedler; Mark Benecke; et al. "Detection of Semen (Human and Boar) and Saliva on Fabrics by a Very High Powered UV-/VIS-Light Source" (PDF). Archived from the original (PDF) on 30 November 2012. Retrieved 2009-12-10.
  82. "Digital Photography of Documents". wells-genealogy.org.uk. Archived from the original on 2012-09-19.
  83. "Integrated Cleaning And Measurement: Defining - What is Clean?". Healthy Facilities Institute. Archived from the original on 21 September 2017. Retrieved 24 June 2017.
  84. "Non-Destructive Inspection: Seeing Through the B-52". US Air Force. Retrieved 24 June 2017.
  85. Escobar, David (20 April 2015). "Oxygen Cleaning: A Validated Process is Critical for Safety". Valve Magazine. Archived from the original on 15 November 2017.
  86. Raj, Baldev; Jayakumar, T.; Thavasimuthu, M. (2002). Practical Non-destructive Testing. Woodhead Publishing. p. 10. ISBN   9781855736009.
  87. "New Investigation Finds Some Hotels Don't Wash Sheets Between Guests". House Beautiful. 15 September 2016. Archived from the original on 3 July 2017.
  88. "What's Hiding in Your Hotel Room?". ABC News. 17 November 2010. Archived from the original on 22 July 2016.
  89. N. E. Battikha (ed), The Condensed Handbook of Measurement and Control 3rd Ed. ISA 2007 ISBN   1-55617-995-2, pp. 65–66
  90. Mervin Fingas (ed.) Oil Spill Science and Technology Elsevier, 2011 ISBN   978-1-85617-943-0 pp. 123–124
  91. "Deep UV Photoresists". Archived from the original on 2006-03-12.
  92. R. V. Lapshin; A. P. Alekhin; A. G. Kirilenko; S. L. Odintsov; V. A. Krotkov (2010). "Vacuum ultraviolet smoothing of nanometer-scale asperities of poly(methyl methacrylate) surface" (PDF). Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques. 4 (1): 1–11. doi:10.1134/S1027451010010015. ISSN   1027-4510. Archived from the original on 9 September 2013.
  93. "The Importance of UV Light for Plants Cultivated Indoors". Best LED Grow Lights Info. 2017-06-11. Retrieved 2017-06-24.
  94. Scott, K.J.; Wills, R.R.H.; Patterson, B.D. (1971). "Removal by ultra-violet lamp of ethylene and other hydrocarbons produced by bananas". Journal of the Science of Food and Agriculture. 22 (9): 496–7. doi:10.1002/jsfa.2740220916.
  95. Scott, KJ; Wills, RBH (1973). "Atmospheric pollutants destroyed in an ultra violet scrubber". Laboratory Practice. 22 (2): 103–6. PMID   4688707.
  96. Shorter, AJ; Scott, KJ (1986). "Removal of ethylene from air and low oxygen atmospheres with ultra violet radiation". Lebensm-Wiss U Technology. 19: 176–9.
  97. Welch, David et.al. (January 2018). "Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases". Scientific Reports. 8 (1): 2752. Bibcode:2018NatSR...8.2752W. doi:10.1038/s41598-018-21058-w. ISSN   2045-2322. PMC   5807439 . PMID   29426899.
  98. "Coming Of Age UV-C LED Technology Update". www.wateronline.com. Archived from the original on 20 April 2017.
  99. "Solar Water Disinfection". Sodis.ch. 2 April 2011. Archived from the original on 25 September 2012. Retrieved 8 November 2011.
  100. Rulfsorchard.com Archived 16 June 2013 at the Wayback Machine
  101. "Video Demos". Archived from the original on 19 December 2014. Retrieved 27 November 2014.
  102. Silberglied, Robert E.; Taylor, Orley R. (1978). "Ultraviolet Reflection and Its Behavioral Role in the Courtship of the Sulfur Butterflies Colias eurytheme and C. philodice (Lepidoptera, Pieridae)". Behavioral Ecology and Sociobiology. 3 (3): 203–43. doi:10.1007/bf00296311.
  103. Meyer-Rochow, V.B.; Järvilehto, M. (1997). "Ultraviolet colours in Pieris napi from northern and southern Finland: Arctic females are the brightest!". Naturwissenschaften. 84 (4): 165–168. Bibcode:1997NW.....84..165M. doi:10.1007/s001140050373.
  104. "UVB Phototherapy". National Psoriasis Foundation, USA. Archived from the original (php) on 22 June 2007. Retrieved 2007-09-23.
  105. "Vitamin D and Ultraviolet Light – a remarkable process". UV Guide UK. Archived from the original on 31 May 2016. Retrieved 13 January 2017.
  106. Margulis, Lynn & Sagan, Dorion (1986). Origins of Sex: Three Billion Years of Genetic Recombination (book). 1. Yale University Press. ISBN   978-0-300-04619-9.

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