1 UV

Ultraviole light on the Windows

Ultraviolet Light

UV light initiated the reaction of S–H bonds with the carbon–carbon double bond in surfactants that cap the nanostructures.

From: Porous Silicon for Biomedical Applications, 2014

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Ultraviolet Light

David J. Elliott, in Ultraviolet Laser Technology and Applications, 1995

Publisher Summary

Ultraviolet (UV) light has become important as the various technologies that are necessary to provide practical UV laser imaging and beam delivery systems have progressed, especially the light sources. UV light has been available only from low power lamps, thereby restricting the usefulness of the technology. The discovery and development of the excimer laser made possible the availability of intense ultraviolet light. Researchers explored and uncovered the unique properties of this new light source. As various phenomena involving UV energy and material interactions were discovered and optimized, practical applications emerged. This chapter discusses the UV spectrum, early UV lamp sources, laser physics and operating principles, and development leading to the discovery of the UV laser. UV light is available from a variety of sources, including naturally occurring UV light, UV lamps, and UV lasers. UV light from the sun is abundant, but cannot be easily or economically harnessed for the applications that have practical value. To a lesser degree, UV lamps have the same problem: they supply rich amounts of the ultraviolet wavelengths, but by the time the energy is collected and transmitted through an optical system, little energy is left to meet the demands of most commercial applications.

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Ultraviolet Light Protection and Stabilization

Michael Tolinski, in Additives for Polyolefins (Second Edition), 2015

Ultraviolet (UV) light can be particularly damaging to polymers like polyolefins, causing degradation and yellowing or color changes, plus surface chalking, cracking, and lower mechanical properties. This chapter covers UV-blocking, -absorbing, and -stabilizing additives. It starts with a basic description of UV light effects on polyolefins. Then the additives' different roles and mechanisms and types are compared to each other in terms of effectiveness, relative costs, and interactions with other additives. Case studies show how the effects of UV have been countered by additives in real applications. And the chapter highlights some important factors to consider when choosing commercially available light stabilizers for specific situations to create resilient polyolefin products.

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The material properties of geosynthetics

S.W. Perkins, in Geosynthetics in Civil Engineering, 2007

2.6.5 Ultraviolet light

UV light is the component of light from the sun with wavelengths shorter than 400 nm. Photons of UV light can break down the chemical bonds (bond scission) of the polymer and lead to degradation of properties. Polyethylene is the most susceptible to UV degradation and can show a 50% strength loss within 4–24 weeks of exposure. Carbon black and other stabilizers are used to provide the polymer with UV protection, which generally means that geosynthetics that are light in colour are more susceptible. Since most geosynthetics are buried in the ground, the issue of UV degradation is important only during transport, storage and construction. During transport and storage, precautions are taken to wrap geosynthetic rolls in a protective cover to prevent UV damage.

For situations where it is important to assess the degradation of geosynthetics to long-term UV exposure, tests can be carried out by exposing geosynthetics to natural or artificial radiation. Sources of artificial radiation includes xenon arc lighting and fluorescent lighting.

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Clean water unit operation design

Seán Moran, in An Applied Guide to Water and Effluent Treatment Plant Design, 2018

UV Irradiation

Ultraviolet (UV) light can be used as a physical disinfectant. A UV disinfection system exposes water to a specific intensity and wavelength of UV for a specific time. The optimum wavelength for water disinfection is about 254 nm.

The UV light is usually produced by mercury vapor lamps housed in quartz sleeves, to allow the lamps to be placed near the water to increase efficiency.

UV transmission is reduced by absorbance by colored compounds such as dissolved iron and manganese as well as scattering by turbidity. Broadly speaking, killing 99% of the bacteria present will require twice as high a dose as that required to kill 90%.

Maximum contaminants for effective UV disinfection are set out in Table 7.9.

Table 7.9. Maximum Contaminants for Effective UV Disinfection

DescriptionAllowable MaximumTransmittance (254 nm, 5 cm pathlength)80%Turbidity15 NTUColor10° hazenIron5 ppmManganese8 ppmCalcium110 ppmTotal organic carbon4 ppm

The system should have the capacity to produce a minimum dose of 25 mWs/cm2, providing a better than 99.999% inactivation of Escherichia coli. For drinking water the United Kingdom's DWI guidelines require the water to be like that dosed with chlorine, e.g., <1 NTU, and validation is a necessity. A dose (or fluence) of 40 mJ/cm2 is common for disinfection but lower values are accepted for Cryptosporidium inactivation.

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UV-protective textiles

Azadeh Bashari, ... Anahita Rouhani Shirvan, in The Impact and Prospects of Green Chemistry for Textile Technology, 2019

12.7 Mechanisms of UV protection finishing agents

UV light causes damage to materials by photo-degradation. Different materials such as natural or synthetic fibers and polymers absorb ultraviolet radiation and undergo a rapid photolytic and photo-oxidative reaction that results in their photo-degradation. The energy of the photons in the ultraviolet region (290–400 nm) is sufficient (315–400 kJ/mol) to break chemical bonds in these materials and to form free radicals. The obtained free radicals react with polymers to form oxy and peroxy radicals and cause to chain rupture until two free radicals are combined together and stable nonradical compounds are formed.

In order to prevent photo-degradation in textiles and negative effect of UV light on skin, organic and inorganic UV-protective finishing agents are used that absorb UVB radiation at 290–320 nm and transform the high UV energy into vibration energy in UV-absorber molecules and then into heat energy in the surrounding without photo-degradation (Schindler and Hauser, 2004).

In inorganic oxides such as TiO2, CeO2, and ZnO are used as UV-protective agents; the UV light is absorbed by excitation of electrons from the valance band to the conduction band. Each of these materials has band gap energies corresponding to absorption spectra and refractive index. Therefore, light below these wavelengths has enough energy to excite electrons and is absorbed by metal oxides. On the other hand, light with wavelength longer than the band gap wavelength will not be absorbed.

Organic UV absorbers are nearly colorless compounds having high absorption coefficients in the UV range of 290–400 nm spectra. These molecules transform the absorbed energy into less harmful vibrational energy before reaching the surrounding materials. For example, compounds with phenolic group which form intramolecular O-H-O bridges, such as salicylates, 2-hydroxybenzophenones, 2,2′-dihydroxy benzophenones, and 3-hydroxy flavones or xantones, and compounds forming OHN bridges, such as 2-(2-hydroxyphenyl) benzotriazoles and 2-(2-hydroxyphenyl)-l,3, 5-triazines, are the most important organic UV absorbers (Kim, 2015).

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ENERGY CONVERSION IN THE CONTEXT OF THE ORIGIN OF LIFE

J. Oró, ... Harold C. Urey, in Living Systems As Energy Converters, 1977

ULTRAVIOLET LIGHT

Ultraviolet light was probably the largest source of energy on the primive earth. The wavelengths absorbed by the atmospheric constituents are those below 2000 Å except for ammonia (≈2300 Å) and H2S (≈2600 Å). Whether it was the most effective source of organic compounds is not clear. Most of the photochemical reactions would occur in the upper atmosphere, and the products formed would, for the most part, absorb at longer wavelengths, and so be decomposed before they reached the protection of the oceans. The yield of amino acids from the photolysis of CH4, NH3 and H2O at wavelengths of 1470 and 1295 Å is quite low, probably due to the low yields of hydrogen cyanide. The synthesis of amino acids by the photolysis of CH4, C2H6, NH3, H2O and H2S mixtures by wavelengths greater than 2000 Å28. is also a low yield synthesis, but the amount of energy is much greater in this region of the sun's spectrum. Only H2S absorbs the ultraviolet light, but the photodissociation of H2S results in a hydrogen atom having a high kinetic energy, which activates or dissociates the methane, ammonia and water. Hot hydrogen atoms generated photochemically from formaldehyde29 and methyl mercaptan have also been used for amino acid synthesis30. These systems appear to be very attractive for prebiotic syntheses. However, it is not clear whether a sufficient partial pressure of H2S could be maintained in the atmosphere since H2S photolyzes rapidly to elemental sulfur and hydrogen.

A photochemical synthesis of formic acid and other low molecular weight organic compounds from CO and water on a silica surface has been reported31. In the gas phase the wavelengths used (2000–3000 Å) are not absorbed by water or CO. However, on the silica surface, either the absorption wavelength of CO or water is greatly shifted or the light is absorbed by the silica surface and the energy transferred to the CO and water32. This reaction may be more relevant for the synthesis of organic compounds on Mars than on the primitive earth. According to the recent organic analyses by Viking landers 1 and 2 at two different sites on the planet Mars, the above reactions do not lead, at least at the present time, to the accumulation of organic compounds that would have been detected by a sensitive gas chromatograph-mass spectrometer33. This is probably because of the highly oxidized nature of the Martian surface. However under the more reducing conditions of a primitive Mars and other similar planetary bodies, such reactions may have played a role in the synthesis of organic compounds and deserve further experimentation.

The role of ultraviolet light in the solar nebula would depend on the opacity of the nebula in the same way as outlined with the solar wind. An estimate of its role is again very model dependent.

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Developments in fibers for technical nonwovens

Y. Yan, in Advances in Technical Nonwovens, 2016

2.4.4.7 Anti-ultraviolet fiber

UV light is an electromagnetic radiation with a wavelength from 400 to 100 nm, shorter than that of visible light. It can be divided into UVA (320–400 nm), UVB (290–320 nm) and UVC (100–290 nm), and only UVA and UVB cannot be absorbed by the ozone layer. In humans, excessive exposure to all bands of UV radiation can result in chronic harmful effects on the skin, eye, and immune system. Overexposure to UVB radiation not only can cause sunburn, but also some forms of skin cancer, so fibers with the function of cutting out the UV become important for personal protective application. Anti-UV fibers are prepared by adding some inorganic additive during fiber processing or during the finishing step, and the used functional additives including ZnO, TiO2, and so on. Their properties can be improved with the decrease of particle size, and nanoparticles attract the most attention in low denier fiber formation.

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Air pollution control in textile industry

B. Purushothama, in Humidification and Ventilation Management in Textile Industry, 2009

12.4 Use of UV disinfestations

Ultraviolet light is part of the spectrum of electromagnetic energy generated by the sun. The full spectrum includes, in order of increasing energy, radio waves, infrared, visible light, ultraviolet, x-rays, gamma rays and cosmic rays. Most sources of light generate some UV. For air disinfection, UV is generated by electric lamps that resemble ordinary fluorescent lamps. Germicidal UV is of a specific type (253.7 nm wavelength) known to kill airborne germs that transmit infections from person to person within work area. This is aimed at the upper room air so that only airborne microbes are directly exposed. Room occupants are exposed only to low levels of reflected UV-levels below that known to cause eye irritation. Germicidal UV has been used safely and effectively in hospitals, clinics and laboratories for more than 60 years. UV does not prevent transmission of infections (e.g. colds) by direct person to person contact.

UV exposure can be very harmful, or harmless, depending on the type of UV, the type of exposure, the duration of exposure, and individual differences in response to UV. There are three types of UV:

UV-C. Also known as 'shortwave' UV, includes germicidal (253.7 nm wavelength) UV used for air disinfection. Unintentional overexposure causes transient redness and eye irritation, but does not cause skin cancer or cataracts.

UV-B. A small, but dangerous part of sunlight. Most solar UV-B is absorbed by the diminishing atmospheric ozone layer. Prolonged exposure is responsible for some type of skin cancer, skin aging, and cataracts (clouding of the lens of the eye).

UV-A. Long-wave UV, also known as 'black-light', the major type of UV in sunlight, responsible for skin tanning, generally not harmful, used in medicine to treat certain skin disorders.

UV air cleaners and ultraviolet water purifiers utilise germicidal UV (UVC) light to enhance the quality of life and well-being through creating a better and healthier indoor environment. The UV disinfection systems, commercial and residential UV air cleaners, literally sterilize micro-organisms. UVC reduces or eliminates germs such as mold, viruses, bacteria, fungi and mold spores from the indoor air of homes, offices and commercial buildings, ensuring a higher indoor air quality.

Studies done by North Carolina Department of Environment, Health and Natural Resources on the air washer portion of a textile air handing system indicated that ultra violet (UV) light, which destroys all micro-organisms (algae, bacteria—including Legionnaires disease, bacteria, fungi, molds, virus), adds nothing to the water, does not alter the pH or cause scaling or other deposits, and requires no special handling or processing. The UV unit can be utilised on both cooling tower and air washers without extensive installation. Further as there is reduction in operation and maintenance cost, no discharge of toxic chemicals, and no extensive maintenance to keep the UV unit operating efficiently, a short payback period and substantial savings are possible.

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Magnetic Particle Testing

Ramesh Singh, in Applied Welding Engineering (Second Edition), 2016

Inspection Under Ultraviolet (Black) Light

Ultraviolet light supplies the correct wavelengths to cause florescent material to fluoresce. The equipment essentially consists of a regulating transformer, a mercury arc lamp, and a filter. The mercury arc bulb and the filter are contained in the reflector lamp housing, and the transformer is housed separately. A deep red-purple filter is designed to pass only the wavelengths of light that will activate the fluorescent material.

For correct test results, the lamp should be able to produce an intensity of minimum 800 μw/cm2 (microwatts per centimeter square) in a 3-in circle at a 15-in distance.

After the switch is turned on, it takes about 5 minutes for the light to attain its full intensity. After being turned on, the light is kept on for the entire duration of the testing to keep the light ready for inspection without interruptions and because frequent switching on and off shortens the life of the arc bulb.

The dust and dirt sticking on the filter glass significantly reduce the intensity of the light. This requires that the filter glass is always kept clean.

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Magnetic Particle Testing

Ramesh Singh, in Applied Welding Engineering, 2012

Viewing Conditions

Non-fluorescent wet particle testing requires that the parts being inspected are illuminated to at least 200 foot candles (2,152 Lux) of visible light.

When using fluorescent material, it is necessary that ultraviolet light is used to view the indications presented by fluorescent particles.

Inspection under Ultraviolet (Black) Light

Ultraviolet light supplies the correct wavelengths to cause fluorescent material to fluoresce. The equipment essentially consists of a regulating transformer, a mercury arc lamp, and a filter. The mercury arc bulb and the filter are contained in the reflector lamp housing and the transformer is housed separately. A deep red-purple filter is designed to transmit only those wavelengths of light that will activate the fluorescent material.

For correct test results, the lamp should be able to produce a minimum intensity of 800 μw/cm2 (microwatts per centimeter squared), in a three-inch circle at a 15-inch distance.

Once the switch is turned on, it takes about five minutes for the light to attain its full intensity. Once turned on the light is kept 'ON' for the entire duration of the test, to keep the light ready for inspection without interruptions, and also because frequent switching on and off shortens the life of the arc bulb.

The dust and dirt sticking on the filter glass significantly reduces the intensity of the light. This means that the filter glass should always be kept clean.

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of electromagnetic radiation beyond (higher in frequency than) light visible to the human eye; radiation with wavelengths from 380 nanometre - 10 nanometre

Ultraviolet colour

Light rays that are outside the visible spectrum at its violet end These rays have a chemical effect upon the dried film of finishing materials Ultraviolet light is commonly used in curing finishes at the factory for prefinished flooring Ultraviolet light also causes woods to lighten or darken See Color Change

A band of the electromagnetic Spectrum between the visible and the X-ray, i e light that is so blue humans cannot see it Photons of ultraviolet light are more energetic than photons of visible light

(U V ) Invisible radiation wavelengths from about 4 nanometers, on the border of the x-ray region, to about 380 nanometers, just beyond the violet in the visible spectrum This frequency of light is considered the culprit in color fading as well as causing skin cancer

1 The invisible rays of the spectrum at the violet end 2 Invisible radiation waves with frequencies shorter than wave lengths of visible light and longer than X-ray

having or employing wavelengths shorter than light but longer than X-rays; lying outside the visible spectrum at its violet end; "ultraviolet radiation"; "an ultraviolet lamp"

electromagnetic radiation of shorter wavelength than visible light UV cannot be seen by the eye, and much of it is absorbed by ozone, a molecule of oxygen, at altitudes of 30-40 km above the Earth Satellite telescopes, however, can and do view stars, galaxies, and the Sun in UV

Electromagnetic radiation that has a wavelength shorter than visible light and longer than x-rays Although it accounts for only 4 to 5 percent of the total energy of insolation, it is responsible for many complex photochemical reactions, such as fluorescence and the formation of ozone

Electromagnetic radiation at wavelengths shorter than the violet end of visible light (5 to 300 nm); the atmosphere of the Earth effectively blocks the transmission of most ultraviolet light

radiation lying in the ultraviolet range; wave lengths shorter than light but longer than X rays having or employing wavelengths shorter than light but longer than X-rays; lying outside the visible spectrum at its violet end; "ultraviolet radiation"; "an ultraviolet lamp

(UV)--electromagnetic radiation resembling visible light, but of shorter wavelength The eye cannot see UV, and much of it is absorbed by ozone, a variant of oxygen, at altitudes of 30-40 km; satellite telescope, however, can and do view stars and the Sun in UV, and even in the extreme UV (EUV), the range between UV and X-rays

{s} beyond the rays of the violet end of the visible light spectrum, of or pertaining to ultraviolet light

There is a naturally imposed bound for distant objects at 912 Angstroms (13 6 eV), the energy needed for a photon to be absorbed by a hydrogen atom and liberate its lone electron in the process There is so much neutral hydrogen in our galaxy that we cannot see very far away at wavelengths shortward of this until about 100 Angstroms, when the absorption by hydrogen (now assisted by other, trace elements) has dropped enough for the interstellar gas to become transparent once again Aside from starlight and synchrotron radiation, the UV contains several very important strong spectral lines from abundant atoms

(1) situated beyond the visible spectrum, just beyond the violet end, having wavelengths shorter than wavelengths of visible light and longer than those of X-rays; (2) relating to, producing, or employing ultraviolet radiation

İlgili Terimler

ultraviolet light: Light in the ultraviolet part of the spectrum

ultraviolet lights: plural form of ultraviolet light

ultraviolet B: electromagnetic radiation with a wavelength of between 280 and 320 nanometers, radiant component of sunlight which causes sunburn and skin cancer, UVB

ultraviolet astronomy: The branch of astronomy that deals with the origin and nature of emissions from extraterrestrial sources in the ultraviolet range of electromagnetic radiation rather than in the visible range. Study of astronomical objects and phenomena by observing the ultraviolet radiation (UV radiation) they emit. It has yielded much information about chemical abundances and processes in interstellar matter, the Sun, and other stellar objects, such as hot young stars and white dwarf stars. Ultraviolet astronomy became feasible once rockets could carry instruments above Earth's atmosphere, which absorbs most electromagnetic radiation of UV wavelengths. Since the early 1960s, a number of unmanned space observatories carrying UV telescopes, including the Hubble Space Telescope, have collected UV data on objects such as comets, quasars, nebulae, and distant star clusters. The Extreme Ultraviolet Explorer, launched in 1992, was the first orbiting observatory to map the sky in the shortest UV wavelengths, at the boundary with the X-ray region of the electromagnetic spectrum

ultraviolet lamp: A lamp, especially a mercury-vapor lamp, that produces ultraviolet light

ultraviolet lamp: any source of illumination that emits ultraviolet radiation

ultraviolet light: Region of the electromagnetic spectrum spanning wavelengths from 91 2 nm to 350 nm, wavelengths largely blocked by the Earth's atmosphere

ultraviolet light: Radiant energy with wave lengths slightly shorter than the visible spectrum Found in sunlight, causes color fading

ultraviolet light: Ultraviolet (UV) light refers to particular colors of light which are so blue that most cannot be seen by the human eye UV light from the Sun reacts highly with many chemicals in the atmosphere and controls many aspects of climate and weather UV light also reacts with human skin to cause suntans and sunburns, which can lead to skin cancer

ultraviolet light: The invisible rays of the sun that penetrate the epidermis and have been proven to cause premature aging and skin cancer

ultraviolet light: Light that is situated beyond the visible spectrum, at the violet end

ultraviolet light: The invisible rays of the spectrum that are outside of the visible spectrum at its short-wavelength violet end Ultraviolet rays are found in everyday sunlight and can cause fading of paint finishes, carpets, and fabrics

ultraviolet light: These devices shoot UV light at the water to kill bacteria They do not get rid of lead or other minerals, so an activated carbon system is required in addition Ideal for farms, rural homes and cottages where non-chlorinated lake or well water is used

ultraviolet light: used as a means of detecting fluorescence in gemstones

ultraviolet light: [n] short wavelength light that is beyond the visible spectrum at the violet end; rays of light that are invisible to the human eye but can damage objects

Ultraviolet Radiation

UV radiation induces both direct and indirect biologic effects, including DNA damage, oxidative stress, depletion of cutaneous defense system, inflammation, immunosuppression, and premature aging of the skin all playing an important role in the generation and maintenance of neoplasms.32,33 UV exposure also leads to the generation of singlet oxygen, hydrogen peroxide (H2O2), and hydroxyl radicals that can cause damage to cellular proteins, lipids and DNA.

From: Polyphenols in Human Health and Disease, 2014

Related terms:

Skin Cancer

Vitamin D

Protein

Neoplasm

Radiation Exposure

DNA

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Melanoma

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Ultraviolet Radiation

Andrew R. Blaustein, Catherine Searle, in Encyclopedia of Biodiversity (Second Edition), 2013

Ultraviolet radiation (UV) can be divided into four wave bands. These are vacuum UV, UV-C (200–280 nm), UV-B (280–315 nm), and UV-A (315–400 nm). At the earth's surface, vacuum UV and UV-C are not present because of their absorption by various gases such as oxygen and ozone. The formation of atmospheric oxygen and a stratospheric ozone layer was essential for the evolution of life on earth. The ozone layer shields the terrestrial surface from harmful UV radiation. Unfortunately, through anthropogenic emissions of chlorofluorocarbons (CFCs) and other gases, the ozone layer has been adversely affected. It has thinned and has developed "holes" in polar regions. Thus, there is potential for increased UV radiation hitting the earth's surface. UV can lead to serious and sometimes irreparable harm. It can cause mutations in cellular DNA, which can ultimately lead to significant alterations in cells, the main cause of cancer. Other damaging effects of UV include premature aging, blindness, and sterilization. UV radiation also has the ability to kill microorganisms, plants, and animals and make them more susceptible to disease by harming immune systems. Besides direct biological effects, UV radiation can have complex effects on biogeochemical processes.

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Skin, Effects of Ultraviolet Radiation

C.R. Shea, Y.Y. He, in Reference Module in Biomedical Sciences, 2014

Molecular Signaling of UVR

UVR alters a variety of cell signaling response to facilitate a protective response or tumorigenic advantage. UVR activates several oncogenic pathways, including epidermal growth factor receptor, Ras, protein kinase C, MAPK, extracellular signal activated regulated kinases, and protein kinase B pathways (Bode and Dong, 2003; Bowden, 2004). UVR upregulates the activation of the stress response kinase p38 pathway and the expression of the proinflammatory and prosurvival protein cyclooxygenase 2. Transcription factors are also targeted by UVR. For example, UVR activates the transcription factors AP1, NF-κB, CREB, and p53. Furthermore, cytokines and their signaling pathways are influenced by UVR. These molecular events may explain how UVR damages skin cells toward cancer or aging.

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Safety Assessment including Current and Emerging Issues in Toxicologic Pathology

Eric D. Lombardini, ... Mark A. Melanson, in Haschek and Rousseaux's Handbook of Toxicologic Pathology (Third Edition), 2013

Part II Ultraviolet Radiation

5 Nature and Action of Ultraviolet Radiation

Ultraviolet radiation (UV) includes wavelengths of electromagnetic energy between 10 and 400 nm, thus bridging the gap between ionizing radiation (X-rays) and visible light. By convention, UV radiation is subdivided into extreme UV (10–120 nm), far UV (120–200 nm), UVC (200–280 nm), UVB (280–320 nm), and UVA (320–400 nm) regions. Sunlight includes all UV wavelengths; however, the Earth's atmosphere attenuates sunlight by processes of absorption and scattering, screening out UV wavelengths shorter than 280 nm. Because of this screening, biologically relevant wavelengths of UV include only the UVA and portions of the UVB regions of the spectrum. Removal of short-wavelength UV is due primarily to stratospheric ozone. Recently, focal thinning of the stratospheric ozone layer has been observed in the spring near the South Pole and attributed to ozone destruction catalyzed by free chlorine released from man-made chlorofluorocarbons. It is predicted that global decreases in stratospheric ozone will result in increased UV exposure and associated adverse health effects. An epidemiological study which examined white populations in Europe, the United States, Canada, and Australia determined that the average increase of skin cancers other than melanoma (i.e., basal cell carcinomas and squamous cell carcinomas) has been 3–8% per year since the 1960s. These rising incidence rates are theorized to be associated with increased UV exposure due to lifestyle changes, as well as increased longevity, and global ozone depletion.

When UV interacts with matter, it behaves as though composed of particles (termed "photons"). The energy of a photon is transferred to the electron of an atom or molecule, resulting in an excited state. The electronic excitation energy is then dissipated by releasing the energy as heat or light, by losing an electron to form a free radical or ion, by using the energy to drive chemical reactions with other molecules, or by undergoing fragmentation. For a molecule or atom to absorb photons of a given wavelength, it must have electrons in appropriate energy levels. Thus, not all molecules absorb all UV wavelengths. A molecule that absorbs a given UV wavelength is a "chromophore" for that wavelength. UV doses are expressed as energy per unit area, typically as Joules/m2. The biological effects of UV depend not only on the total energy of UV absorbed, but also on the wavelength of that energy. The "action spectrum" expresses the functional relationship between biological effect and wavelength for a given UV dose. Action spectroscopy can help identify the UV chromophore ultimately responsible for initiating a given biological response. Studies of the action spectrum for UV-induced skin cancer indicate that the most effective wavelengths are those that can penetrate the skin and damage DNA, suggesting that DNA is a major chromophore for this response.

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Reflexive Physical Therapies

Jan Zbigniew Szopinski MD, PhD, in The Biological Action of Physical Medicine, 2014

5.5.2 Ultraviolet Radiation

UV is an invisible electromagnetic radiation characterized by the wavelength ranging from 100–400 nm. In the electromagnetic radiation spectrum, it is located between the ranges of a visible violet radiation and so-called soft X-rays. For therapeutic purposes, the UV wavelength range of 200–400 nm is used. Depending on its biological impact, the UV can be divided as follows:

•

Range A: wavelength from 400–315 nm

•

Range B: wavelength from 315–280 nm

•

Range C: wavelength from 280–200 nm

The Schumann's UV of the wavelength ranging from 100–200 nm has no practical medical importance, because it is almost entirely absorbed by the air and the water vapor.

Various substances show various degrees of UV absorption. Quartz, which passes the radiation of the wavelength longer than 180 nm well, is widely used in UV lamps. Standard window glass, however, passes only the radiation of wavelengths longer than 320 nm. Chance–Crookes's glass absorbs the UV entirely and therefore is widely used in protective sunglasses.

UV is well absorbed by human skin, so it can penetrate inside the human body only up to 2 mm deep. Therefore, any therapeutic influence of the UV on the tissues located deeper under the skin can be best explained in the reflexive way. We also have to remember that part of the applied UV is reflected from the skin; this depends on the application angle, the condition of the skin, and the UV wavelength.

The UV causes so-called photochemical reactions: photosynthesis, photolysis, and photoisomerization. Photochemical reactions are responsible for, among other things, the creation of photochemical erythema in the skin, pigment creation, and vitamin D production. The UV bactericidal effect (particularly at the 250–270 nm wavelength) is also based on the photochemical reactions that lead to the structural changes in bacterial proteins and to blockage of the vital processes.

The term photochemical erythema describes the reddish skin coloration that is due to the dilatation of local blood vessels. The photochemical erythema's intensity depends on the UV wavelength, the intensity of the UV emission, the duration of the UV application, the distance between the source of radiation and the skin, skin sensitivity (especially the size of the epidermis), general carnation—blondes are more sensitive than brunettes—and age—children are more sensitive than adults.

There is a characteristic evolution of the photochemical erythema that includes the following phases:

•

Latent period of the duration from one to six hours. Absorption of the UV by the epidermis cell proteins leads to their denaturation and cell damage. From damaged cells histamine and other vasodilating substances are released, causing dilation and increased permeability of the skin capillary vessels.

•

Intensification period covers the time between appearances of the first symptoms of vasodilation and the maximal erythema's intensity, which usually takes place within six to 24 hours after exposure to the UV. During this period of time, a skin edema can appear, sometimes with water blisters between the skin layers. Excessively strong UV dosages can lead to irreversible damage and necrosis of the epidermic cells.

•

Disappearance period of the duration from some hours to some days, depending on the UV dosage absorbed. As a result of the photochemical erythema, an epidermal thickening, scaling, and brownish skin discoloration (due to pigment accumulation) can be observed.

Contrary to the thermal erythema caused by the IR, the photochemical erythema includes a latent period, is solid, and is limited strictly to the exposed skin area. The IR application to skin area with the photochemical erythema can weaken the intensity and accelerate the disappearance of a photochemical erythema. Also, local nerve damage can weaken or even prevent the appearance of a photochemical erythema that indicates an important role of the reflexive mechanism in UV therapy. Certain chemical substances can significantly increase body sensitivity to UV, including coal tar, sulphonamides, tetracyclines, chlorpropamid, tolbutamol, promethazinum, diazepam, and salicylamids. So-called photodynamic agents, especially psoralens, are used to increase the efficacy of UV therapy. Increased sensitivity to UV can also be seen in certain diseases, including lupus erythematosus, porphyria, dermatomyositis, and xeroderma pigmentosum.

The UV application improves local blood supply and stimulates a higher metabolic rate; therefore, the skin becomes more elastic, looks younger, and is more resistant to infections. For these reasons, UV is widely used for cosmetic purposes (in sunbeds, for example). For the same reasons, UV therapy is also successfully used in the management of wounds, bedsores, and chronic skin ulcerations. The wavelength of more than 280 nm is usually used for these purposes, because wavelengths shorter than this cause epidermic damage. The A range of UV is widely used in the photochemotherapy ultraviolet A (PUVA), which combines the UV (especially wavelengths of 360–365 nm) with photodynamic agents and which is a therapy of choice in psoriasis and other skin diseases. The so-called selective UV-phototherapy (SUP) uses the wavelength from 300–340 nm and does not require photodynamic agents.

Prophylactic application of UV is commonly used in vitamin D shortages, especially as a prevention of rachitis. Special bactericidal UV lamps are commonly used in hospitals, health centers, and laboratories. However, physical medicine mainly applies UV in skin diseases (see previous note; also, acne vulgaris), alopecia areata, soft tissue inflammations, arthritis, neuralgias, bronchial asthma, nose and throat diseases (using special applicators), and even endocrine hypofunctions (thyroid and ovaries).

There are various kinds of UV generators available on the market. They can be portable for local use (Figure 5.4), but there are also special chambers (sunbeds, for example) for general applications (Figure 5.5). Depending on their technical parameters and special filters, they offer a variety of therapeutic options. Because UV overdose can lead to burns, tissue necrosis, and other serious complications, it is of utmost importance to follow the individual instruction manuals strictly, especially with regard to the range of applied wavelengths, the intensity of UV emission (including the distance from the UV source), and the treatment duration. Both the patient and the therapist must protect their eyes with special glasses.

FIGURE 5.4. Local UV therapy.

FIGURE 5.5. UV general application by means of a sunbed.

UV therapy is generally contraindicated in cases of malignant tumors and also traditionally in active pulmonary TB as well as epilepsy.

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Carcinogenesis

F.R. de Gruijl, H.N. Ananthaswamy, in Comprehensive Toxicology, 2010

14.09.1.1 Basic Impact

Ultraviolet (UV) radiation is a ubiquitous carcinogen present in sunlight. Its mutagenicity was already demonstrated in the 1930s and the wavelength dependence was found to parallel the absorption spectrum of DNA (Hollaender and Emmons 1941) with a peak around 265 nm instead of 280 nm as expected for proteins (1 nm = 10−9 m). A similar spectral analysis had earlier revealed that the germicidal effect of UV radiation was also attributable to DNA absorption (Gates 1928). The short-wavelength, germicidal, and mutagenic UV radiation from the sun probably had free access to the surface of the primordial Earth through an anoxic atmosphere, thus creating a very harsh environment in which any unshielded form of early cellular life would not have had much of a chance of surviving. With the introduction of oxygen in the atmosphere about 2.5 billion years ago and the subsequent development of a stratospheric ozone layer (Goldblatt et al. 2006), the most harmful UV radiation with wavelengths below 290 nm (see Figure 1) was blocked. According to the Berkner–Marshal hypothesis (Berkner and Marshall 1965) this was a prerequisite for the successful colonization of land masses some 2 billion years later by multicellular organisms that were able to cope with a 3 orders of magnitude lower genotoxicity from the remnant UV radiation (Rettberg et al. 1998).

Figure 1. Electromagnetic spectrum of sunlight that reaches the Earth's surface. The UV region encompasses wavelengths 200–400 nm. This region is subdivided into UV-A (320–400 nm), UV-B (280–320 nm), and UV-C (200–280 nm). Wavelengths in the UV-B and to a certain extent, UV-A, are biologically relevant to human skin cancer.

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PROCESS HYGIENE | Risk and Control of Airborne Contamination

G.J. Curiel, H.L.M. Lelieveld, in Encyclopedia of Food Microbiology (Second Edition), 2014

Inactivation by Ultraviolet Light

UV radiation can be used to kill microorganisms in air. UV radiation has a wavelength range between about 210 and 328 nm, with maximal bactericidal activity near the wavelength 260 nm of peak absorption of DNA. Bacterial spores are generally more resistant to UV light than vegetative cells. UV light systems are now available for treating airflow entering a sterile area. Air disinfection systems are fitted into ductwork, and microorganisms present are deactivated as they are exposed to the UV source. UV can also be used to disinfect air for pressurizing tanks or pipelines. A disadvantage of UV is that it is not effective if microorganisms are protected by particles or embedded in dust, due to shade effects.

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Packaging: Aseptic Filling

R.S. Chavan, ... S. Bhatt, in Encyclopedia of Food and Health, 2016

UV Irradiation

UV radiation is effective in inactivating vegetative bacteria but relatively ineffective in reducing bacterial spores, as a long exposure time is required to achieve desired sterility. Sterilization by UV irradiation is becoming increasingly prevalent, especially for packaging materials and machines that are less readily sterilized by H2O2. UV radiation promotes lipid oxidation in food; hence, safety issues need to be considered in designing sterilization processes. UV irradiation induces a mutation of DNA in microorganisms, which ultimately gives a germicidal effect. To accomplish four to six decimal reductions in microbial counts on a flat surface, a dosage of 250 mW cm− 2 is required. The factors that assure the effectiveness of UV irradiation are smoothness of packaging materials and dust-free surfaces.

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Fern Extract, Oxidative Stress, and Skin Cancer

Concepción Parrado, ... Salvador Gonzalez, in Cancer, 2014

Fernblock® Prevents UV Radiation-Mediated Immunosuppression

UV radiation induces immunosuppression, anergy, and immunological tolerance. This is mediated by a marked decrease of the numbers of eLCs, which leads to T helper 1 lymphocyte (Th1) clonal anergy.42

The decrease of eLC, which decreases the level of immune surveillance in the skin, is likely related to the role of UV radiation in promoting immune evasion by tumor cells.43,44 Additional correlative evidence is provided by organ transplant patients undergoing immunosuppressive therapy, who have an elevated risk of developing both nonmelanoma skin cancer and melanoma, especially in cases of history of frequent sun exposure.45

PL efficiently blocked epidermal LC depletion upon UV irradiation and prevented the appearance of abnormal dendritic cell (DC) morphologies.11,12,29 Similar results were obtained using blood dendritic cells (DC) irradiated using a solar simulator. In these experiments, PL inhibited DC apoptosis and promoted secretion of anti-inflammatory cytokines and inhibited expression of pro-inflammatory cytokines (e.g., TNF-α) by irradiated DC.53 The molecular mechanism of enhanced DC survival seems to implicate inhibition of trans-urocanic acide (UCA) isomerization,46 blockade of iNOS expression induced by UV radiation, which generates altered nitrogen oxide metabolites that cause immunosuppression by eliminating skin DC and enhancement of endogenous systemic antioxidant systems that lead to decreased oxidized intermediates (e.g., oxidized glutathione;29 Table 25.3).

TABLE 25.3. Beneficial Effects of Fernblock® in Inflammation Induced by UV Radiation

In Vitro StudiesIn Vivo StudiesMolecular Mechanism/Cellular TargetReferenceHuman keratinocytesInhibition of UVR-induced increase of TNF-α

Inhibition of UVR-induced increase of NO and iNOS40Human keratinocytesInhibition of the IVR-induced activation of NFκB and AP-140Hairless albino mice (Skh-1)Reduction UVR-induced mast cell infiltration39Hairless Xpc(+/-) miceInhibition of the UVR-induced neutrophil and macrophage infiltration16Hairless Xpc(+/-) miceInhibition of the UVR-induced COX-2 expression16HumanInhibition of PUVA-induced vasodilation11HumanReduction UVR-induced mast cell infiltration11 ,12

Photoimmunosuppression has been related to trans-UCA interaction (Table 25.4).47 Trans-UCA (trans-UCA;(2E)-3-(1H-imidazol-4-yl)prop-2-enoic acid) is a deamination product of histidine, present at a high concentration in the stratum corneum. Trans-UCA shows a similar UV radiation-absorption spectrum as the UV wavelength dependence for immune suppression and upon exposure to UV radiation, trans-UCA photoisomerizes to its cis-isomer. In addition to alterations in antigen presentation and processing, the immunosuppressive effects of UV radiation are mediated by immunomodulatory molecules, which include both pro-inflammatory and anti-inflammatory molecules such as prostaglandin (PG) E2, TNF-α, and IL-10.48

TABLE 25.4. Beneficial Effects of Fernblock® in Photoimmunosuppression

In Vitro StudiesIn Vivo StudiesMolecular Mechanism/Cellular TargetReferenceHistochemicalPL interferes with the cis-UCA isomerization implicated in photoimmunosuppression46Human keratinocytesInhibition of expression of pro-inflammatory cytokines such as TNF-α40Immature human DCsProtects DCs from UV-induced apoptosis43Immature human DCsInduces DCs production of anti-inflammatory cytokines (IL-12)43C57BL/6 miceInhibition of local and systemic photoimmunosuppression51Hairless ratsReduction of glutathione oxidation in blood and epidermis29Hairless ratsReduction of glutathione oxidation in blood and epidermis29HumanInhibition of UVR-mediated Langerhans cell depletion.11, 12

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Melanoma

Tara C. Gangadhar, ... Lynn M. Schuchter, in Abeloff's Clinical Oncology (Fifth Edition), 2014

Primary Prevention

UVR exposure is the only modifiable risk factor for melanoma. Protection from UVR is the primary strategy to decrease melanoma risk; optimal use of sunscreen and sun protection results in a decreased risk of melanoma.22 Protection from UVR can mitigate one's risk for skin cancer, regardless of the age at which it is implemented. Standard recommendations to decrease UVR exposure include avoidance of the sun between the peak hours of 10 am to 4 pm, seeking shade whenever possible, covering the skin surface with sun-protective clothing including wide-brimmed hats, long-sleeved shirts, long pants, and sunglasses, and using broad-spectrum sunscreen with a sun protection factor (SPF) of 15 or greater to cover exposed skin surfaces. Regular application of SPF 15+ sunscreen in adults has been demonstrated to decrease melanoma risk in a randomized trial.23 Appropriate type, timing, frequency, and amount of sunscreen applied are important factors in effective primary prevention. The United States Food and Drug Administration (FDA) has legislated regulations for over-the-counter sunscreens (http://www.fda.gov/forconsumers/consumerupdates/ucm258416.htm). Highlights of these new regulations are that sunscreen products that protect against both UVA and UVB radiation will be labeled "broad spectrum" and "SPF 15" (or higher) on the front label; sunscreen products that are not broad spectrum or that are broad spectrum with SPF values from 2 to14 will be labeled with a warning; and the front label must limit water resistance claims to either 40 minutes or 80 minutes, based on standard testing to determine how much time a user can expect to get the declared SPF level of protection while swimming or sweating. Sun-protective clothing guards the skin from UVR more effectively than sunscreen. As opposed to sunscreen, which is frequently applied unevenly and insufficiently, sun-protective clothing provides uniform and constant protection for the areas it covers. The UVR-protective properties of clothing vary according to the thickness, color, and type of fabric. Most regulatory agencies have adopted the UV protection factor as the standard of measurement of UV protection for clothing. Clothing can achieve a UV protection factor >500, which is vastly superior to sunscreen. Barriers to the implementation of sun protection behaviors include discomfort from sun-protective clothing, inconvenience of applying sunscreen, and denial of personal risk for skin cancer. Furthermore, studies indicate that tanning may be an addictive behavior. Recent legislation may help to decrease access of minors to indoor tanning salons; however, modifying exposure to natural UVR remains a challenge.

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Water Disinfection for International Travelers

Howard Backer, in Travel Medicine (Fourth Edition), 2019

Ultraviolet.

UV radiation is widely used to sterilize water used in beverages and food products, for secondary treatment of wastewater, and to disinfect drinking water at the community and household level (see Table 5.3). In sufficient doses of energy, all waterborne enteric pathogens are inactivated by UV radiation.29 The ultraviolet waves must strike the organism, so the water must be free of particles that could act as a shield.51 UV rays do not alter the water, but they also do not provide any residual disinfecting power. The requirement for power has limited its adaptation for field use; however, portable, battery-operated units are available for disinfection of small quantities of water. Also larger units are available where power is accessible (see Table 5.4).

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