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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
G. Shama, in Encyclopedia of Food Microbiology (Second Edition), 2014
Abstract
Ultraviolet light (UV) forms part of the electromagnetic spectrum, and it can be harnessed to inactivate microorganisms associated with foods and food-processing operations. The most effective wavelengths for direct inactivation of microorganisms lie in the so-called UV-C region of the electromagnetic spectrum. A number of UV sources are in current use, but low-pressure mercury sources are relatively efficient emitters of germicidal UV and these sources traditionally have been used to disinfect liquids, air, and the surfaces of solids, including foods. UV has also been used in conjunction with other treatments, most notably peroxidation, to bring about synergistic disinfection. Systems can be put in place to enable a wide variety of foods to be treated with UV in such a way as to avoid unnecessary overexposure which might result in loss of quality.
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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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Disinfection by-products in drinking water: detection and treatment methods
S. Hariganesh, ... S. Rangabhashiyam, in Disinfection By-products in Drinking Water, 2020
12.1.1.2 Ultraviolet disinfection
Ultraviolet (UV) light disinfection involves exposing microorganisms to intense UV light. The UV light deteriorates the DNA of the microorganisms, so that they would be unable to reproduce and cause diseases (https://www.water). UV disinfection is effective for bacteria, viruses, and parasites. UV disinfection is most effective on water pretreated with coagulation and filtration. The method of ultraviolet light disinfection presented decreased efficiency in the presence of more dust particles. Because the dust particles would prevent the microorganisms from complete exposure of UV rays Betancourt and Rose (2004). If any unwanted material settles on the glass sleeve, the microorganisms will not receive proper light intensity, they will reproduce and cause disease. With UV disinfection, pretreatment may need to include water softening and/or iron removal processes. The protective glass shield must be maintained properly and must be replaced if damaged by poor quality water (Wolfe, 1990).
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Food Safety Management
V. Kakurinov, in Encyclopedia of Food Safety, 2014
UV Light Irradiation
UV light is one of the systems used for air disinfection as UV germicidal irradiation (UVGI) is considered UV light with wavelength of 2537 Å (254 nm). UV lamps for air disinfection can be part of low-power systems (lamp ratings from 15 to 100 W) or part of more powerful systems (medium pressure arc tubes with ratings from 0.5 to 5 kW). Most commonly used in UVGI applications are low-pressure mercury (Hg) discharge lamps.
According to Brown, dose needed for one decimal reduction varies widely between species (e.g., for Legionella pneumofilia – 2 mW s cm−2 and for Aspergillus niger – 132 mW s cm−2).
UV light irradiation has two mayor drawbacks. One is that microorganisms which are in the shade will be not destroyed. That means that the UVGI lamps should be located in a manner that does not allow occurrence of shadows. The second drawback is that UV light with high intensity can cause eye cataracts and skin cancer. That is why, as a part of the designing systems, it is essential to establish proper screening and interlock devices.
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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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Drinking Water Quality and Treatment
Dan Askenaizer, in Encyclopedia of Physical Science and Technology (Third Edition), 2003
VII.D Ultraviolet (UV) Irradiation Technology
UV light is electromagnetic energy that is located in the electromagnetic spectrum at wavelengths between those of X-rays and visible light. UV light that is effective is destroying microbial entities in located in the 200- to 310- nm range of the energy spectrum. Most typical applications of UV at water treatment plants apply UV light in the wavelength range of 250 to 270 nm. Most lamps emit UV irradiation by passing an electrical arc between filaments in a pressurized gas or vapor (typically mercury vapor). Ultraviolet dosage is commonly measured as milliWatt-second per square centimeter (mW-s/cm2) or milliJoule per square centimeter (mJ/cm2).
Typically a UV process is designed such that water flows in a narrow region around a series of UV lamps. Microorganisms in water are inactivated through exposure to the UV light. In general, a molecule in the ground state absorbs electromagnetic energy from the UV source and the bonds in the molecule are transformed to an excited state, and chemical and physical processes become thermodynamically possible. The process works on the principle that UV energy disrupts the DNA of the microorganisms and prevents it from reproducing.
There are four types of UV technologies of interest to the water industry. They include (1) low-pressure, low-intensity UV technology; (2) low-pressure, medium-intensity UV technology; (3) medium-pressure, high-intensity UV technology; and (4) pulsed-UV technology. Unlike using disinfectants such as ozone, chlorine, or chlorine dioxide, UV irradiation does not provide oxidation for color, taste, and odor control because UV light is not a strong oxidant.
A UV treatment process is comprised of a series of UV lamps enclosed inside a quartz sleeve. The UV light passes through the quartz sleeve and into the water. Due to the high energy emitted by the UV lamps, the temperature of the quartz sleeve can rise substantially causing the precipitation of various scales on the surface of the sleeve, thus blocking the passage of the UV light into the water and dramatically reducing the efficiency of the process. The scales are commonly caused by the precipitation of calcium, iron, or magnesium salts. Preventing the buildup of this scale is a major operational challenge for the use of UV. One of the current problems facing the use of UV irradiation is determining the actual UV dose the water receives, because measuring a residual is not possible.
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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
Physical Disinfection
Physical treatments tend to be energy intensive, and leave no residual. This is an advantage when used for treating water to be discharged to environment, or ultrapure water, but not for drinking water treatment. Heat has been used at small scale, but UV light is popular for small to medium scale potable and ultrapure applications. Other types of electromagnetic radiation, including gamma radiation, have been used. However, gamma radiation is unpopular, despite its effectiveness, due to the added complexities of handling radioactive materials.
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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Heat, solar pasteurization, and ultraviolet radiation treatment for removal of waterborne pathogens
Sanchayita Rajkhowa, in Waterborne Pathogens, 2020
4.1 Electromagnetic spectrum of ultraviolet light and microbial inactivation
UV light, being a part of the electromagnetic spectrum, exists between 10 and 400 nm. UV light is divided into four regions: UV-A (315–400 nm), UV-B (280–315 nm), UV-C (200–280 nm), and UV-V (100–200 nm) (Fig. 9.5).

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Figure 9.5. The electromagnetic spectrum.
The microorganism inactivation ability by UV light is proportional to the product of light intensity and time of exposure, i.e., commonly termed as UV dose and expressed in the units of W s/cm2 or J/cm2.
UV dose=UV light intensity(W/cm2)×time of exposure(s)
However, the actual UV dose received by the pathogens varies with the flow rate of water inside the UV chamber, the structure of the chamber, and transmission efficiency of the contaminated water. Much lower dosages of UV radiation are sufficient for inactivation of most of the pathogens, viz., bacteria and viruses while protozoans require relatively higher dosages for the same (Table 9.3). Slade et al. (1986) have compared the disinfection efficiency for groundwater contamination by chlorination and UV radiation processes and reported that UV radiation is potentially a more capable disinfection technique than the former (Slade et al., 1986). Recent commercially available UV systems for water purification are designed to provide UV dosage of 25,000–35,000 μW s/cm2, sufficient enough to inactivate 90% of almost all species of bacteria and viruses present in water.
Table 9.3. Ultraviolet dosages4 and log reduction5∗ for 90% inactivation of selected pathogens.(∗UV dose is in mJ/cm2 unit)
PathogenDosage (μW s/cm2)Log10 reductionBacteriaEscherichia coli3,0003.5Salmonella typhi2,500<2Pseudomonas aeruginosa5,5005.5Salmonella enteritis4,0005Shigella dysenteriae2,2002.2Shigella para dysenteriae1,7001.68Shigella flexneri1,7001.7Shigella sonnei3,0003.2Staphylococcus aureus4,5002.6Legionella pneumophila3801.9Vibrio cholerae3,4000.8VirusPoliovirus 15,0005Coliphage3,600-Hepatitis A virus3,7005.5Rotavirus SA 118,0009.1ProtozoaGiardia muris82,000<1.9Acanthamoeba castellanii35,000–
UV radiation ranging from 200 to 300 nm is known to be an effective source of germicide for a broad spectrum of microorganisms absorbing maximum radiation at around 260 nm (UV-C) that eventually damages their DNA structure and makes them inactive further. These wavelengths deteriorate the DNA strands of microorganisms through dimerization of pyrimidine bases. It is found that the formation of UV-C-induced cyclobutane pyrimidine dimers and other photodimeric lesions depend on the magnitude (wavelength) of radiation absorbed (Kuluncsics et al., 2007; Besaratinia et al., 2011). During dimerization, rupture and/or damage of DNA sequences inactivates the microorganisms by means of preventing their replication, translation, and transcription. However, on exposure to visible light, most pathogens develop a reversible mechanism against the dimerization of nucleic acid molecules (present in DNAs) to repair the damage that occurred by the absorption of UV radiation. For example, dimerization of thymine can be reversed in the presence of visible light and can repair the UV-damaged DNA. This process of repairing DNAs is known as photoreactivation (Wolfe, 1990), which reduces the efficiency of UV treatment. A transient dose of UV never ensures absolute inactivation of pathogens present in the entire volume of water under treatment. Therefore, it is important to treat each volume part of water with sufficient dose of UV radiation to get rid of the maximum amount of pathogens.
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