HOME

TheInfoList




Ultraviolet (UV) is a form of
electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. ...

electromagnetic radiation
with
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase (waves), phase on the wave, such as two adja ...

wavelength
from 10 nm (with a corresponding frequency around 30
PHz
PHz
) to 400 nm (750
THz
THz
), shorter than that of
visible light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nano ...
, but longer than
X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Moti ...

X-ray
s. UV radiation is present in
sunlight Sunlight is a portion of the given off by the , in particular , , and light. On , sunlight is and through , and is obvious as when the Sun is above the . When direct is not blocked by s, it is experienced as sunshine, a combination of b ...

sunlight
, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by
electric arc An electric arc, or arc discharge, is an of a that produces a prolonged . The through a normally medium such as produces a ; the plasma may produce . An arc discharge is characterized by a lower voltage than a and relies on of electrons fr ...

electric arc
s and specialized lights, such as
mercury-vapor lamp A mercury-vapor lamp is a that uses an through vaporized to produce .http://www.handlebar-online.com/articles/what-color-is-mercury-discharge-tube/ The arc discharge is generally confined to a small mounted within a larger bulb. The outer ...
s,
tanning lamp Tanning lamps (sometimes called tanning bulbs in the United States or tanning tubes in Europe) are the part of a tanning bed, booth or other tanning device which produces ultraviolet light responsible for indoor tanning. There are hundreds of di ...
s, and
black light A blacklight (or often black light), also referred to as a UV-A light, Wood's lamp, or ultraviolet light, is a that emits long-wave () and very little . One type of lamp has a violet material, either on the bulb or in a separate glass fil ...

black light
s. Although long-wavelength ultraviolet is not considered an
ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of s or s that have sufficient to s or s by detaching s from them. The particles generally travel at a speed that is greater than 1% of , and the electromagnetic w ...
because its
photon The photon ( el, φῶς, phōs, light) is a type of elementary particle In , an elementary particle or fundamental particle is a that is not composed of other particles. Particles currently thought to be elementary include the fundamental s ...

photon
s lack the energy to
ionize Ionization or ionisation is the process by which an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday ...
atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of ato ...

atom
s, it can cause
chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and t ...

chemical reaction
s and causes many substances to glow or
fluoresce light. Fluorescence is the emission of light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the human eye. Visible light is usually defi ...

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. Short-wave ultraviolet light damages
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
and sterilizes surfaces with which it comes into contact. For humans,
suntan
suntan
and
sunburn Sunburn is a form of radiation burn A radiation burn is a damage to the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. ...

sunburn
are familiar effects of exposure of the skin to UV light, along with an increased risk of
skin cancer Skin cancers are cancer Cancer is a group of diseases A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not due to any immediate external ...

skin cancer
. The amount of UV light produced by the Sun means that the Earth would not be able to sustain life on dry land if most of that light were not filtered out by the atmosphere. More energetic, shorter-wavelength "extreme" UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground. However, ultraviolet light (specifically, UVB) is also responsible for the formation of
vitamin D Vitamin D is a group of fat-soluble secosteroid 250px, The parent steroid skeleton. The B-ring of the parent steroid is broken between C9 and C10 to yield D vitamins. A secosteroid () is a type of steroid , hypothetical a steroid with ...
in most land
vertebrates Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...
, including humans. The UV spectrum, thus, has effects both beneficial and harmful to life. The lower wavelength limit of human vision is conventionally taken as 400 nm, so ultraviolet rays are invisible to humans, although people can sometimes perceive light at shorter wavelengths than this. Insects, birds, and some mammals can see near-UV (NUV) (i.e., slightly shorter wavelengths than what 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 The cornea is the transparent Transparency, transparence or transparent most often refer to transparency and translucency, the physical property of allowing the transmission of light through a material. They may also refer to: Literal uses * ...

cornea
. Humans also lack color receptor adaptations for ultraviolet rays. Nevertheless, the
photoreceptors
photoreceptors
of the
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well ...

retina
are sensitive to near-UV, and people lacking a lens (a condition known as
aphakia Aphakia is the absence of the lens A lens is a transmissive optical Optics is the branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , ...
) perceive near-UV as whitish-blue or whitish-violet. Under some conditions, children and young adults can see ultraviolet down to wavelengths around 310 nm. Near-UV radiation is visible to insects, some mammals, and some
birds Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four-chambered , and a strong yet lightweight . Birds live worldwide and range in size from the to the . There ar ...
. Birds have a fourth color receptor for ultraviolet rays; this, coupled with eye structures that transmit more UV gives smaller birds "true" UV vision.


History and discovery

"Ultraviolet" means "beyond violet" (from
Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in relation with") is "an appa ...

Latin
''ultra'', "beyond"), violet being the color of the highest frequencies of
visible light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nano ...

visible light
. Ultraviolet has a higher frequency (thus a shorter wavelength) than violet light. UV radiation was discovered in 1801 when the German physicist
Johann Wilhelm Ritter Johann Wilhelm Ritter (16 December 1776 – 23 January 1810) was a German German(s) may refer to: Common uses * of or related to Germany * Germans, Germanic ethnic group, citizens of Germany or people of German ancestry * For citizens of Germany ...

Johann Wilhelm Ritter
observed that invisible rays just beyond the violet end of the visible spectrum darkened
silver chloride Silver chloride is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by havin ...

silver chloride
-soaked paper more quickly than violet light itself. He called them "(de-)oxidizing rays" (german: de-oxidierende Strahlen) to emphasize
chemical reactivity In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they under ...
and to distinguish them from "
heat rays
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 John William Draper (May 5, 1811 – January 4, 1882) was an English-born American scientist, philosopher, physician, chemist, historian and photographer. He is credited with producing the first clear photograph of a female face (1839–40) and ...

John William Draper
, who named them "tithonic rays"). The terms "chemical rays" and "heat rays" were eventually dropped in favor of ultraviolet and
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

infrared
radiation upThe international symbol for types and levels of ionizing radiation (radioactivity) that are unsafe for unshielded humans. Radiation, in general, exists throughout nature, such as in light and sound. In physics Physics (from grc ...

radiation
, respectively. In 1878, the sterilizing effect of short-wavelength light by killing bacteria was discovered. By 1903, the most effective wavelengths were known to be around 250 nm. In 1960, the effect of ultraviolet radiation on DNA was established. 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 German physicist Victor Schumann.The also protects living beings from this.


Subtypes

The
electromagnetic spectrum The electromagnetic spectrum is the range of frequencies Frequency is the number of occurrences of a repeating event per unit of time A unit of time is any particular time Time is the indefinite continued sequence, progress of existe ...

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 The International Organization for Standardization (ISO ) is an international standard-setting body composed of representatives from various national standards organizations. Founded on 23 February 1947, the organization develops and publish ...
ISO-21348: Several 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
photodiode A photodiode is a semiconductor p–n junction device that converts light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the human eye. Visib ...

photodiode
s and
photocathodeA photocathode is a surface engineered to convert light (photons The photon ( el, φῶς, phōs, light) is a type of elementary particle In particle physics, an elementary particle or fundamental particle is a subatomic particle that is not comp ...
s, which can be tailored to be sensitive to different parts of the UV spectrum. Sensitive UV
photomultiplierA photomultiplier is a device that converts incident photons into an electrical signal. Kinds of photomultiplier include: * Photomultiplier tube, a vacuum tube A vacuum tube, an electron tube, valve (British usage) or tube (North America), i ...

photomultiplier
s are available.
Spectrometer A spectrometer () is a scientific instrument used to separate and measure Spectrum, spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon ...

Spectrometer
s and
radiometer 210px, An example of a Crookes radiometer. The vanes rotate when exposed to light, with faster rotation for more intense light, providing a quantitative measurement of electromagnetic radiation intensity. A radiometer or roentgenometer is a device ...

radiometer
s are made for measurement of UV radiation. Silicon detectors are used across the spectrum. Vacuum UV, or VUV, wavelengths (shorter than 200 nm) are strongly absorbed by molecular
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
in the air, though the longer wavelengths around 150–200 nm can propagate through
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
. Scientific instruments can, therefore, use 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 In manufacturing, photolithography or optical lithography is a general term for techniques that use to produce minutely patterned s of suitable materials over a substrate, such as a , to protect selected areas of it during subsequent , , or op ...
equipment (for
semiconductor manufacturing Semiconductor device fabrication is the process used to manufacture semiconductor devices A semiconductor A semiconductor material has an Electrical resistivity and conductivity, electrical conductivity value falling between that of a El ...
) and
circular dichroism Circular dichroism (CD) is dichroism Lampworked dichroic glass bead In optics, a dichroic material is either one which causes visible light to be split up into distinct beams of different wavelengths (colours) (not to be confused with Dispersion (o ...

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 electron In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s 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 synthesizing multilayer optics that reflect up to about 50% of EUV radiation at normal incidence is possible. This technology was pioneered by the
NIXT The NIXT, or Normal Incidence X-ray Telescope, was a sounding rocket A sounding rocket or rocketsonde, sometimes called a research rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during ...
and
MSSTA The Multi-spectral solar telescope array, or MSSTA, was a sounding rocket A sounding rocket or rocketsonde, sometimes called a research rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments du ...
sounding rockets in the 1990s, and it has been used to make telescopes for solar imaging. See also the
Extreme Ultraviolet Explorer The Extreme Ultraviolet Explorer (EUVE) was a space telescope A space telescope or space observatory is a telescope located in outer space Outer space is the expanse that exists beyond Earth and between astronomical object, celestia ...
satellite In the context of spaceflight Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either human spaceflight, with or uncrewed spaceflight, without humans on board. Most spaceflight ...

satellite
. Some sources use the distinction of "hard UV" and "soft UV". For instance, in the case of astrophysics, the boundary may be at the
Lyman limitThe Lyman limit is the short-wavelength end of the hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pur ...
(wavelength 91.2 nm), with "hard UV" being more energetic; the same terms may also be used in other fields, such as
cosmetology Cosmetology (from Greek , ''kosmētikos'', "beautifying"; and , '' -logia'') is the study and application of beauty treatment. Branches of specialty include hairstyling, skin care, cosmetics Cosmetics are constituted from a mixture of ch ...
,
optoelectronic Opto-electronics (or optronics) is the study and application of electronic devices and systems that source, detect and control light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that ...
, etc. The numerical values 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.


Solar ultraviolet

Very hot objects emit UV radiation (see
black-body radiation Black-body radiation is the within or surrounding a body in with its environment, emitted by a (an idealized opaque, non-reflective body). It has a specific spectrum of wavelengths, inversely related to intensity that depend only on the bod ...
). The
Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

Sun
emits ultraviolet radiation at all wavelengths, including the extreme ultraviolet where it crosses into X-rays at 10 nm. Extremely hot
star A star is an astronomical object consisting of a luminous spheroid of plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral) or heliotrope, a mineral aggregate * Quark ...

star
s emit proportionally more UV radiation than the Sun.
Sunlight Sunlight is a portion of the given off by the , in particular , , and light. On , sunlight is and through , and is obvious as when the Sun is above the . When direct is not blocked by s, it is experienced as sunshine, a combination of b ...

Sunlight
in space at the top of Earth's atmosphere (see
solar constant The solar constant (''GSC'') is a flux density measuring mean solar electromagnetic radiation In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature') ...
) is composed of about 50% infrared light, 40% visible light, and 10% ultraviolet light, for a total intensity of about 1400 W/m2 in vacuum. The atmosphere blocks about 77% of the Sun's UV, when the Sun is highest in the sky (at zenith), with absorption increasing at shorter UV wavelengths. At ground level with the sun at zenith, sunlight is 44% visible light, 3% ultraviolet, and the remainder infrared. Of the ultraviolet radiation that reaches the Earth's surface, more than 95% is the longer wavelengths of UVA, with the small remainder UVB. Almost no UVC reaches the Earth's surface. The fraction of UVB which remains in UV radiation after passing through the atmosphere is heavily dependent on cloud cover and atmospheric conditions. On "partly cloudy" days, patches of blue sky showing between clouds are also sources of (scattered) UVA and UVB, which are produced by
Rayleigh scattering Rayleigh scattering ( ), named after the nineteenth-century British physicist Lord Rayleigh (John William Strutt), is the predominantly elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength o ...

Rayleigh scattering
in the same way as the visible blue light from those parts of the sky. UVB also plays a major role in plant development, as it affects most of the plant hormones. During total overcast, the amount of absorption due to clouds is heavily dependent on the thickness of the clouds and latitude, with no clear measurements correlating specific thickness and absorption of UVB. The shorter bands of UVC, as well as even more-energetic UV radiation produced by the Sun, are absorbed by oxygen and generate the ozone in the
ozone layer
ozone layer
when single oxygen atoms produced by UV
photolysis Photodissociation, photolysis, or photodecomposition is a chemical reaction in which a chemical compound is broken down by photons. It is defined as the interaction of one or more photons with one target molecule. Photodissociation is not limited ...
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, absorbers, and windows

Ultraviolet absorbers are molecules used in organic materials (
polymers A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repeat unit, repeating subunits. Due to thei ...

polymers
,
paints Paint is any pigmented liquid A liquid is a nearly incompressible In fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics Mechanics (Ancient Greek, Greek: ) is the area of physics concerned wi ...

paints
, etc.) to absorb UV radiation to reduce the
UV degradation In polymer chemistry photo-oxidation (sometimes: oxidative photodegradationPhotodegradation is the alteration of materials by light. Typically, the term refers to the combined action of sunlight Sunlight is a portion of the electromagnetic ...
(photo-oxidation) of a material. The absorbers can themselves degrade over time, so monitoring of absorber levels in weathered materials is necessary. In
sunscreen Sunscreen, also known as sunblock or suntan lotion, is a photoprotective topical A topical medication is a medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug use ...
, ingredients that absorb UVA/UVB rays, such as
avobenzone
avobenzone
,
oxybenzone Oxybenzone or benzophenone-3 or BP-3 (trade name A trade name, trading name, or business name is a pseudonym used by companies that do not operate under their registered company name. The term for this type of alternative name is a "fictitious" ...

oxybenzone
and
octyl methoxycinnamate
octyl methoxycinnamate
, are organic chemical absorbers or "blockers". They are contrasted with inorganic absorbers/"blockers" of UV radiation such as
carbon black Carbon black (subtypes are acetylene black, channel black, furnace black, lamp black and thermal black) is a material produced by the incomplete combustion of heavy petroleum Petroleum, also known as crude oil and oil, is a naturally occ ...

carbon black
,
titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical ...
, and
zinc oxide Zinc oxide is an inorganic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...

zinc oxide
. For clothing, the ultraviolet protection factor (UPF) represents the ratio of
sunburn Sunburn is a form of radiation burn A radiation burn is a damage to the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. ...

sunburn
-causing UV without and with the protection of the fabric, similar to
sun protection factor Sunscreen, also known as suncream, sunblock or suntan lotion, is a lotion A lotion is a low-viscosity topical preparation intended for application to the skin. By contrast, Cream (pharmaceutical), creams and gels have higher viscosity, typical ...
(SPF) ratings for
sunscreen Sunscreen, also known as sunblock or suntan lotion, is a photoprotective topical A topical medication is a medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug use ...
. Standard summer fabrics have UPFs around 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 , owner = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = ESA Headquarters in Paris, France, 2 ...

ESA
Mars rover mission, since they will remain unfaded by the high level of UV present at the surface of Mars. Common
soda–lime glass Soda–lime glass, also called soda–lime–silica glass, is the most prevalent type of glass, used for windowpanes and glass containers (bottles and jars) for beverages, food, and some commodity items. Some glass bakeware is made of soda-lime ...
, such as window glass, is partially
transparent Transparency, transparence or transparent most often refer to transparency and translucency, the physical property of allowing the transmission of light through a material. They may also refer to: Literal uses * Transparency (photography), a sti ...
to UVA, but is
opaque Opacity or opaque may refer to: * Impediments to (especially, visible) light: ** Opacities, absorption coefficients ** Opacity (optics), property or degree of blocking the transmission of light * Metaphors derived from literal optics: ** Opaque con ...
to shorter wavelengths, passing about 90% of the light above 350 nm, but blocking over 90% of the light below 300 nm. A study found that car windows allow 3-4% of ambient UV to pass through, especially if the UV was greater than 380 nm. Other types of car windows can reduce transmission of UV that is greater than 335 nm.
Fused quartz Fused quartz, fused silica or quartz glass is a glass Glass is a non- crystalline, often transparency and translucency, transparent amorphous solid, that has widespread practical, technological, and decorative use in, for example, window pa ...
, depending on quality, can be transparent even to
vacuum UV Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, ...
wavelengths. Crystalline
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tetrahedra, ...

quartz
and some crystals such as CaF2 and MgF2 transmit well down to 150 nm or 160 nm wavelengths.
Wood's glass Two "black-light" ultraviolet fluorescent tubes. The glass envelopes illustrate the dark blue color of Wood's glass, although these modern tubes actually use another optical filtering material. Wood's glass is an optical filter glass invented in 1 ...
is a deep violet-blue barium-sodium silicate glass with about 9%
nickel oxide Nickel oxide may refer to: * Nickel(II) oxide, NiO, green, well-characterised oxide * Nickel(III) oxide, Ni2O3, black, not well-characterised oxide * Oxonickelates {{Chemistry index ...
developed during
World War I World War I, often abbreviated as WWI or WW1, also known as the First World War or the Great War, was a global war A world war is "a war engaged in by all or most of the principal nations of the world". The term is usually reserved for ...

World War I
to block visible light for covert communications. It allows both infrared daylight and ultraviolet night-time communications by being transparent between 320 nm and 400 nm and also the longer infrared and just-barely-visible red wavelengths. Its maximum UV transmission is at 365 nm, one of the wavelengths of
mercury lamp mercury-vapor light approximately 15 seconds after starting. mercury vapor lamp. The small diagonal cylinder at the bottom of the arc tube is a resistor which supplies current to the starter electrode. A mercury-vapor lamp is a gas-discharge la ...
s.


Artificial sources


"Black lights"

A ''black light'' lamp emits long-wave UV‑A radiation and little visible light. Fluorescent black light lamps work similarly to other
fluorescent lamps light. Fluorescence is the emission of light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the human eye. Visible light is usually defi ...
, but use a
phosphor A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or ...

phosphor
on the inner tube surface which emits UV‑A radiation instead of visible light. Some lamps use a deep-bluish-purple
Wood's glass Two "black-light" ultraviolet fluorescent tubes. The glass envelopes illustrate the dark blue color of Wood's glass, although these modern tubes actually use another optical filtering material. Wood's glass is an optical filter glass invented in 1 ...
optical filter that blocks almost all visible light with wavelengths longer than 400 nanometers. The purple glow given off by these tubes is not the ultraviolet itself, but visible purple light from mercury’s 404 nm spectral line which escapes being filtered out by the coating. Other black lights 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 small 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 Two "black-light" ultraviolet fluorescent tubes. The glass envelopes illustrate the dark blue color of Wood's glass, although these modern tubes actually use another optical filtering material. Wood's glass is an optical filter glass invented in 1 ...
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 Fluorescence is the emission of light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as ha ...

fluorescence
'', the colored glow that many substances give off when exposed to UV light. UV‑A / UV‑B emitting bulbs are also sold for other special purposes, such as
tanning lamp Tanning lamps (sometimes called tanning bulbs in the United States or tanning tubes in Europe) are the part of a tanning bed, booth or other tanning device which produces ultraviolet light responsible for indoor tanning. There are hundreds of di ...
s and reptile-husbandry.


Short-wave ultraviolet lamps

Shortwave UV lamps are made using a
fluorescent lamp A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor that uses to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet light that then causes a coating ...

fluorescent lamp
tube with no phosphor coating, composed of
fused quartz Fused quartz, fused silica or quartz glass is a glass Glass is a non- crystalline, often transparency and translucency, transparent amorphous solid, that has widespread practical, technological, and decorative use in, for example, window pa ...
or
vycor Vycor is the brand name of Corning's high-silica, high-temperature glass Glass is a non- crystalline, often transparency and translucency, transparent amorphous solid, that has widespread practical, technological, and decorative use in, for ex ...
, since ordinary glass absorbs UV‑C. These lamps emit ultraviolet light with two peaks in the UV‑C band at 253.7 nm and 185 nm due to the
mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

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. The fused quartz tube passes the 253.7 nm radiation but blocks the 185 nm wavelength. Such tubes have two or three times the UV‑C power of a regular fluorescent lamp tube. These low-pressure lamps have a typical efficiency of approximately 30–40%, meaning that for every 100 watts of electricity consumed by the lamp, they will produce approximately 30–40 watts of total UV output. They also emit bluish-white visible light, due to mercury's other spectral lines. These "germicidal" lamps are used extensively for disinfection of surfaces in laboratories and food-processing industries, and for disinfecting water supplies.


Incandescent lamps

'Black light'
incandescent lamp image of the tungsten filament of an incandescent light bulb An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire #Filament, filament heated until it glows. The filament is enclosed in a gla ...

incandescent lamp
s are also made from an incandescent light bulb with a filter coating which absorbs most visible light.
Halogen lamps A halogen lamp, also known as a tungsten halogen, quartz-halogen or quartz iodine lamp, is an incandescent lamp image of the tungsten filament of an incandescent light bulb An incandescent light bulb, incandescent lamp or incandescent ligh ...

Halogen lamps
with
fused quartz Fused quartz, fused silica or quartz glass is a glass Glass is a non- crystalline, often transparency and translucency, transparent amorphous solid, that has widespread practical, technological, and decorative use in, for example, window pa ...
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 lamp Gas-discharge lamps are a family of artificial light sources that generate light by sending an electric discharge An electric discharge is the release and transmission of electricity in an applied electric field through a medium such as a gas. ...
s containing different gases produce UV radiation at particular spectral lines for scientific purposes.
Argon Argon is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...

Argon
and
deuterium arc lamp A deuterium arc lamp (or simply deuterium lamp) is a low-pressure gas-discharge light source often used in spectroscopy Spectroscopy is the study of the interaction between matter In classical physics and general chemistry, matter is any s ...

deuterium arc lamp
s are often used as stable sources, either windowless or with various windows such as
magnesium fluoride Magnesium fluoride is an inorganic compound with the chemical formula, formula MgF2. The compound is a white crystalline salt (chemistry), salt and is transparent over a wide range of wavelengths, with commercial uses in optics that are also used i ...

magnesium fluoride
. These are often the emitting sources in UV spectroscopy equipment for chemical analysis. Other UV sources with more continuous emission spectra include xenon arc lamps (commonly used as sunlight simulators),
deuterium arc lamp A deuterium arc lamp (or simply deuterium lamp) is a low-pressure gas-discharge light source often used in spectroscopy Spectroscopy is the study of the interaction between matter In classical physics and general chemistry, matter is any s ...

deuterium arc lamp
s, mercury-xenon arc lamps, and s. The
excimer lampAn excimer lamp (or excilamp) is a source of ultraviolet light produced by spontaneous emission of excimer (exciplex) molecules. Introduction Excimer lamps are quasimonochromatic light sources operating over a wide range of wavelengths in the u ...
, 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

Light-emitting diodes A light-emitting diode (LED) is a semiconductor A semiconductor material has an value falling between that of a , such as metallic copper, and an , such as glass. Its falls as its temperature rises; metals behave in the opposite ...
(LEDs) can be manufactured to emit radiation in the ultraviolet range. In 2019, following significant advances over the preceding five years, UV‑A LEDs of 365 nm and longer wavelength were available, with efficiencies of 50% at 1.0 W output. Currently, the most common types of UV LEDs that can be found / purchased are in 395 nm and 365 nm wavelengths, both of which are in the UV‑A spectrum. When referring to the wavelength of the UV LEDs, the rated wavelength is the peak wavelength that the LEDs put out, and light at both higher and lower wavelength frequencies near the peak wavelength are present, which is important to consider when looking to apply them for certain purposes. The cheaper and more common 395 nm UV LEDs are much closer to the visible spectrum, and LEDs not only operate at their peak wavelength, but they also give off a purple color, and end up not emitting pure UV light, unlike other UV LEDs that are deeper into the spectrum. Such LEDs are increasingly used for applications such as
UV curing UV curing (ultraviolet curing) is the process by which ultraviolet light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗ ...
applications, charging glow-in-the-dark objects such as paintings or toys, and they are becoming very popular in a process known as retro-brighting, which speeds up the process of refurbishing / bleaching old plastics and portable flashlights for detecting counterfeit money and bodily fluids, 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 photo-initiator and resin formulators, makes the expansion of LED cured UV materials likely. UV‑C LEDs are developing rapidly, but may require testing to verify effective disinfection. Citations for large-area disinfection are for non-LED UV sources known as
germicidal lamp A germicidal lamp is an electric light that produces ultraviolet C (UVC) light. This short-wave ultraviolet light disrupts DNA base pairing, causing formation of pyrimidine dimers, and leads to the inactivation of bacteria, viruses, and protoz ...
s. Also, they are used as line sources to replace
deuterium lamp A deuterium arc lamp (or simply deuterium lamp) is a low-pressure gas-discharge light source often used in spectroscopy Spectroscopy is the study of the interaction between matter In classical physics and general chemistry, matter is any s ...
s in
liquid chromatography In chemical analysis Analytical chemistry studies and uses instruments and methods used to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combine ...

liquid chromatography
instruments.


Ultraviolet lasers

Gas laser A gas laser is a laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term "laser" originated as an acronym for "light amplification by stim ...
s,
laser diode A packaged laser diode shown with a penny for scale The laser diode chip removed and placed on the eye of a needle for scale A laser diode (LD, also injection laser diode or ILD, or diode laser) is a semiconductor A semiconductor mater ...

laser diode
s, and
solid-state laser A solid-state laser is a laser that uses a active laser medium, gain medium that is a solid, rather than a liquid as in dye lasers or a gas as in gas lasers. Semiconductor-based lasers are also in the solid state, but are generally considered as a s ...
s can be manufactured to emit ultraviolet rays, and lasers are available that cover the entire UV range. The
nitrogen gas laser A nitrogen laser is a gas laser operating in the ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowle ...
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 nm in wavelength. Another type of high-power gas lasers are
excimer laser An excimer laser, sometimes more correctly called an exciplex laser, is a form of ultraviolet laser which is commonly used in the production of microelectronic devices, semiconductor based integrated circuits or "chips", eye surgery, and microelectr ...
s. They are widely used lasers emitting in ultraviolet and vacuum ultraviolet wavelength ranges. Presently, UV argon-fluoride excimer lasers operating at 193 nm are routinely used in
integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuit 200px, A circuit built on a printed circuit board (PCB). An electronic circuit is composed of indiv ...

integrated circuit
production by
photolithography In manufacturing, photolithography or optical lithography is a general term for techniques that use to produce minutely patterned s of suitable materials over a substrate, such as a , to protect selected areas of it during subsequent , , or op ...
. 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. UV diode-pumped solid state lasers have been demonstrated using
cerium Cerium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that ...

cerium
- doped lithium strontium aluminum fluoride crystals (Ce:LiSAF), a process developed in the 1990s at
Lawrence Livermore National Laboratory Lawrence Livermore National Laboratory (LLNL) is a federal research facility in Livermore, California Livermore (formerly Livermores, Livermore Ranch, and Nottingham) is a city in Alameda County, California, in the United States. With an es ...
. Wavelengths shorter than 325 nm are commercially generated in
diode-pumped solid-state laser A diode-pumped solid-state laser (DPSSL) is a solid-state laser made by laser pumping, pumping a solid gain medium, for example, a ruby or a Nd:YAG laser, neodymium-doped YAG crystal, with a laser diode. DPSSLs have advantages in compactness and ef ...
s. Ultraviolet lasers can also be made by applying frequency conversion to lower-frequency lasers. Ultraviolet lasers have applications in industry (
laser engraving Laser engraving is the practice of using lasers to engrave an object. Laser marking, on the other hand, is a broader category of methods to leave marks on an object, which also includes color change due to chemical/molecular alteration, charring, ...
), medicine (
dermatology Dermatology is the branch of medicine Medicine is the science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the f ...
, and keratectomy), chemistry (
MALDI In mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the of s. The results are presented as a ', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used in many different ...

MALDI
), free-air secure communications, computing (
optical storage IBM International Business Machines Corporation (IBM) is an American multinational technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in 1911, founded in Endicott, New York, as ...
), and manufacture of integrated circuits.


Tunable vacuum ultraviolet (VUV)

The vacuum ultraviolet (V‑UV) 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) or metal vapors (e.g. magnesium). By making one of the lasers tunable, the V‑UV can be tuned. If one of the lasers is resonant with a transition in the gas or vapor then the V‑UV production is intensified. However, resonances also generate wavelength dispersion, and thus the phase matching can limit the tunable range of the 4 wave mixing. Difference frequency mixing (i.e., ) as an advantage over sum frequency mixing because the phase matching can provide greater tuning. In particular, difference frequency mixing two photons of an (193 nm) excimer laser with a tunable visible or near IR laser in hydrogen or krypton provides resonantly enhanced tunable V‑UV covering from 100 nm to 200 nm. Practically, the lack of suitable gas / vapor cell window materials above the
lithium fluoride Lithium fluoride is an inorganic compound with the chemical formula LiF. It is a colorless solid, that transitions to white with decreasing crystal size. Although odorless, lithium fluoride has a bitter-saline taste. Its structure is analogous to ...
cut-off wavelength limit the tuning range to longer than about 110 nm. Tunable V‑UV wavelengths down to 75 nm was achieved using window-free configurations.


Plasma and synchrotron sources of extreme UV

Lasers have been used to indirectly generate non-coherent extreme UV (E‑UV) radiation at 13.5 nm for
extreme ultraviolet lithography Extreme may refer to: Science and mathematics Mathematics * Extreme point, a point in a convex set which does not lie in any open line segment joining two points in the set * Maxima and minima, extremes on a mathematical function Science * Extrem ...
. The E‑UV is not emitted by the laser, but rather by electron transitions in an extremely hot tin or xenon plasma, which is excited by an excimer laser. This technique does not require a synchrotron, yet can produce UV at the edge of the X‑ray spectrum.
Synchrotron light source A synchrotron light source is a source of electromagnetic radiation (EM) usually produced by a storage ring, for scientific and technical purposes. First observed in synchrotrons, synchrotron light is now produced by storage rings and other sp ...
s can also produce all wavelengths of UV, including those at the boundary of the UV and X‑ray spectra at 10 nm.


Human health-related effects

The impact of ultraviolet radiation on
human health Health, according to the World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations United Nations Specialized Agencies are autonomous organizations working with the United Nations and eac ...
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.


Beneficial effects

UV light (specifically, UV‑B) causes the body to produce
vitamin D Vitamin D is a group of fat-soluble secosteroid 250px, The parent steroid skeleton. The B-ring of the parent steroid is broken between C9 and C10 to yield D vitamins. A secosteroid () is a type of steroid , hypothetical a steroid with ...
, which is essential for life. Humans need some UV radiation to maintain adequate vitamin D levels. According to the World Health Organization
There is no doubt that a little sunlight is good for you! But 5–15 minutes of casual sun exposure of hands, face and arms two to three times a week during the summer months is sufficient to keep your vitamin D levels high.
Vitamin D can also be obtained from food and supplementation. Excess sun exposure produces harmful effects, however. Vitamin D promotes the creation of
serotonin Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter Monoamine neurotransmitters are s and s that contain one group connected to an by a two-carbon chain (such as -CH2-CH2-). Examples are , and . All monoamines are ...

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


Skin conditions

UV rays also treat certain skin conditions. Modern phototherapy has been used to successfully treat
psoriasis Psoriasis is a long-lasting, noncontagious autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. There are at least 80 types of autoimmune diseases. Nearly any body part c ...

psoriasis
,
eczema Dermatitis is of the , typically characterized by iness, and a . In cases of short duration, there may be small s, while in long-term cases the skin may become . The area of skin involved can vary from small to covering the entire body. Derma ...

eczema
,
jaundice Jaundice, also known as icterus, is a yellowish or greenish pigmentation of the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and s ...

jaundice
,
vitiligo Vitiligo is a long-term skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic org ...

vitiligo
,
atopic dermatitis Atopic dermatitis (AD), also known as atopic eczema, is a long-term type of inflammation of the skin (dermatitis). It results in puritis, itchy, red, swollen, and cracked skin. Clear fluid may come from the affected areas, which often thickens ov ...

atopic dermatitis
, and localized
scleroderma Scleroderma is a group of autoimmune diseases that may result in changes to the human skin, skin, blood vessels, muscles, and internal organs. The disease can be either localized to the skin or involve other organs, as well. Symptoms may include ...
. In addition, UV light, in particular UV‑B radiation, has been shown to induce
cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA (DNA replication In , DNA replication is the of pro ...

cell cycle
arrest in
keratinocytes Keratinocytes are the primary type of cell found in the epidermis The epidermis is the outermost of the three layers that comprise the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate Ver ...
, the most common type of skin cell. 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.


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 retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well ...

retina
. The risk is elevated at high
altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference and a point or object. The exact definition and reference datum varies according to the context (e.g. ...

altitude
s and people living in high
latitude In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. The first person to use the ...

latitude
areas where snow covers the ground right into early summer and sun positions even at
zenith The zenith is an imaginary point directly "above" a particular location, on the imaginary celestial sphere. "Above" means in the vertical direction (plumb line) opposite to the gravity direction at that location (nadir). The zenith is the "high ...

zenith
are low, are particularly at risk. Skin, the
circadian A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., endogenous Endogenous substa ...
system, and the
immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as Tumor immunology, cancer cells and objects such ...
can also be affected. The differential effects of various wavelengths of light on the human cornea and skin are sometimes called the "erythemal action spectrum". The action spectrum shows that UVA does not cause immediate reaction, but rather UV begins to cause
photokeratitis Photokeratitis or ultraviolet keratitis is a painful eye condition caused by exposure of insufficiently protected eyes to the ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength In physics Physi ...
and skin redness (with lighter skinned individuals being more sensitive) at wavelengths starting near the beginning of the UVB band at 315 nm, and rapidly increasing to 300 nm. The skin and eyes are most sensitive to damage by UV at 265–275 nm, which is in the lower UV‑C band. At still shorter wavelengths of UV, damage continues to happen, but the overt effects are not as great with so little penetrating the atmosphere. The
WHO The World Health Organization (WHO) is a specialized agency of the United Nations United Nations Specialized Agencies are autonomous organizations working with the United Nations and each other through the co-ordinating machinery of the Unite ...

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 UV‑A and UV‑B bands.


Skin damage

Overexposure to UV‑B radiation not only can cause
sunburn Sunburn is a form of radiation burn A radiation burn is a damage to the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. ...

sunburn
but also some forms of
skin cancer Skin cancers are cancer Cancer is a group of diseases A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not due to any immediate external ...

skin cancer
. However, the degree of redness and eye irritation (which are largely not caused by UV‑A) do not predict the long-term effects of UV, although they do mirror the direct damage of DNA by ultraviolet. All bands of UV radiation damage
collagen Collagen () is the main structural protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowder ...

collagen
fibers and accelerate aging of the skin. Both UV‑A and UV‑B destroy vitamin A in skin, which may cause further damage. UVB radiation can cause direct DNA damage. This cancer connection is one reason for concern about
ozone depletion Ozone depletion consists of two related events observed since the late 1970s: a steady lowering of about four percent in the total amount of ozone in Earth, Earth's atmosphere (the ozone layer), and a much larger springtime decrease in stratosphe ...

ozone depletion
and the ozone hole. The most deadly form of
skin cancer Skin cancers are cancer Cancer is a group of diseases A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not due to any immediate external ...

skin cancer
, malignant
melanoma Melanoma, also redundantly known as malignant melanoma, is a type of skin cancer that develops from the Biological pigment, pigment-producing cells known as melanocytes. Melanomas typically occur in the skin, but may rarely occur in the mouth, i ...

melanoma
, is mostly caused by DNA damage independent from UV‑A radiation. This can be seen from the absence of a direct UV signature mutation in 92% of all melanoma. Occasional overexposure and sunburn are probably greater risk factors for melanoma than long-term moderate exposure. UV‑C is the highest-energy, most-dangerous type of ultraviolet radiation, and causes adverse effects that can variously be mutagenic or carcinogenic. In the past, UV‑A was considered not harmful or less harmful than UV‑B, but today it is known to contribute to skin cancer via
indirect DNA damage 500px, Indirect DNA damage: The chromophore absorbs UV-light (* denotes an excited state), and the energy of the excited state is creating singlet oxygen (1O2) or a hydroxyl radical (•OH), which then damages DNA through oxidation. Indirect D ...

indirect DNA damage
(free radicals such as reactive oxygen species). UV‑A 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 UV‑A consists mostly of single-strand breaks in DNA, while the damage caused by UV‑B includes direct formation of thymine dimers or
cytosine dimer Pyrimidine dimers are molecular lesion A molecular lesion, or a point lesion, is damage to the structure of a biological molecule such as DNA, RNA, or protein Proteins are large biomolecules or macromolecules that are comprised of one or more ...
s and double-strand DNA breakage. UV‑A 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. UVB photons can cause direct DNA damage. UV‑B radiation excited state, excites DNA molecules in skin cells, causing aberrant covalent bonds to form between adjacent pyrimidine bases, producing a pyrimidine dimers, dimer. Most UV-induced pyrimidine dimers in DNA are removed by the process known as nucleotide excision repair that employs about 30 different proteins. Those pyrimidine dimers that escape this repair process 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 human skin color, 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 DNA damage, direct and
indirect DNA damage 500px, Indirect DNA damage: The chromophore absorbs UV-light (* denotes an excited state), and the energy of the excited state is creating singlet oxygen (1O2) or a hydroxyl radical (•OH), which then damages DNA through oxidation. Indirect D ...

indirect DNA damage
from the UV. UV‑A gives a quick tan that lasts for days by oxidizing melanin that was already present and triggers the release of the melanin from melanocytes. UV‑B yields a tan that takes roughly 2 days to develop because it stimulates the body to produce more melanin.


Sunscreen safety debate

Medical organizations recommend that patients protect themselves from UV radiation by using
sunscreen Sunscreen, also known as sunblock or suntan lotion, is a photoprotective topical A topical medication is a medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug use ...
. Five sunscreen ingredients have been shown to protect mice against skin tumors. However, Potential health risks of sunscreen, some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells. The amount of sunscreen that penetrates into the lower layers of the skin may be large enough to cause damage. Sunscreen reduces the direct DNA damage that causes sunburn, by blocking UV‑B, and the usual Sun Protection Factor, SPF rating indicates how effectively this radiation is blocked. SPF is, therefore, also called UVB-PF, for "UV‑B protection factor". This rating, however, offers no data about important protection against UVA, 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 UV‑A filters may be the cause of the higher incidence of melanoma found in sunscreen users compared to non-users. Some sunscreen lotions contain
titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical ...
,
zinc oxide Zinc oxide is an inorganic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...

zinc oxide
, and , which help protect against UV‑A rays. The photochemical properties of melanin make it an excellent photoprotection, photoprotectant. However, sunscreen chemicals cannot dissipate the energy of the excited state as efficiently as melanin and therefore, if sunscreen ingredients penetrate into the lower layers of the skin, the amount of reactive oxygen species may be increased. The amount of sunscreen that penetrates through the stratum corneum may or may not be 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. The study indicates that sunscreen must be reapplied within 2 hours in order to prevent UV light from penetrating to sunscreen-infused live skin cells.


Aggravation of certain skin conditions

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


Eye damage

The eye is most sensitive to damage by UV in the lower UV‑C band at 265–275 nm. Radiation of this wavelength is almost absent from sunlight but is found in welder's arc lights and other artificial sources. Exposure to these can cause "welder's flash" or "arc eye" (
photokeratitis Photokeratitis or ultraviolet keratitis is a painful eye condition caused by exposure of insufficiently protected eyes to the ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength In physics Physi ...
) and can lead to cataracts, pterygium and pinguecula formation. To a lesser extent, UV‑B in sunlight from 310 to 280 nm also causes photokeratitis ("snow blindness"), and the
cornea The cornea is the transparent Transparency, transparence or transparent most often refer to transparency and translucency, the physical property of allowing the transmission of light through a material. They may also refer to: Literal uses * ...

cornea
, the Lens (anatomy), lens, and the
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well ...

retina
can be damaged. 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. Ordinary, untreated eyeglasses give some protection. Most plastic lenses give more protection than glass lenses, because, as noted above, glass is transparent to UV‑A and the common acrylic plastic used for lenses is less so. Some plastic lens materials, such as polycarbonate, inherently block most UV.


Degradation of polymers, pigments and dyes

UV degradation In polymer chemistry photo-oxidation (sometimes: oxidative photodegradationPhotodegradation is the alteration of materials by light. Typically, the term refers to the combined action of sunlight Sunlight is a portion of the electromagnetic ...
is one form of polymer degradation that affects plastics exposed to
sunlight Sunlight is a portion of the given off by the , in particular , , and light. On , sunlight is and through , and is obvious as when the Sun is above the . When direct is not blocked by s, it is experienced as sunshine, a combination of b ...

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. 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 Fluorescence is the emission of light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as ha ...

fluorescence
in materials, ultraviolet radiation has a number of applications. The following table gives some uses of specific wavelength bands in the UV spectrum *''13.5 nm'': Extreme ultraviolet lithography *''30–200 nm'': Photoionization, ultraviolet photoelectron spectroscopy, standard
integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuit 200px, A circuit built on a printed circuit board (PCB). An electronic circuit is composed of indiv ...

integrated circuit
manufacture by
photolithography In manufacturing, photolithography or optical lithography is a general term for techniques that use to produce minutely patterned s of suitable materials over a substrate, such as a , to protect selected areas of it during subsequent , , or op ...
*''230–365 nm'': UV-ID, label tracking, barcodes *''230–400 nm'': Optical sensors, various instrumentation *''240–280 nm'': Disinfection, decontamination of surfaces and water (
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
absorption has a peak at 260 nm),
germicidal lamp A germicidal lamp is an electric light that produces ultraviolet C (UVC) light. This short-wave ultraviolet light disrupts DNA base pairing, causing formation of pyrimidine dimers, and leads to the inactivation of bacteria, viruses, and protoz ...
s *''200–400 nm'': Forensic analysis, drug detection *''270–360 nm'': Protein analysis, DNA sequencing, drug discovery *''280–400 nm'': Medical imaging of cell (biology), cells *''300–320 nm'': Light therapy in medicine *''300–365 nm'': curing (chemistry), Curing of polymers and printer inks *''350–370 nm'': Bug zappers (flies are most attracted to light at 365 nm)


Photography

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. 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. EPROMs (Erasable Programmable Read-Only Memory) are erased by exposure to UV radiation. These modules have a transparent (
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tetrahedra, ...

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. Amusement parks often use UV lighting to fluoresce ride artwork and backdrops. This often has the side effect of causing rider's white clothing to glow light-purple. 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 Phosphor banded stamp, 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 Forensic science, 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. 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, liquid penetrant inspection) or they may be bound to ferrite particles caught in magnetic leakage fields in ferrous materials (magnetic-particle inspection, 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. 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. UV/VIS spectroscopy, 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.


Sanitary compliance

Ultraviolet light helps detect organic material deposits that remain on surfaces where periodic cleaning and sanitizing may have failed. It is used in the hotel industry, manufacturing, and other industries where levels of cleanliness or contamination are Inspection, inspected. Perennial news features for many television news organizations involve an investigative reporter using a similar device to reveal unsanitary conditions in hotels, public toilets, hand rails, and such.


Chemistry

UV/Vis spectroscopy is widely 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. In environmental chemistry, UV radiation could also be used to detect Contaminants of emerging concern in water samples. 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. Ultraviolet radiation can detect thin sheens of oil spill, 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. Ultraviolet lamps are also used as part of the analysis of some minerals and gemstone, gems.


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 Sunlight is a portion of the given off by the , in particular , , and light. On , sunlight is and through , and is obvious as when the Sun is above the . When direct is not blocked by s, it is experienced as sunshine, a combination of b ...

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 Infrared, 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 thermal radiation, radiation in the UVC band, whereas the
Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

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-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Moti ...

X-ray
s 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 In manufacturing, photolithography or optical lithography is a general term for techniques that use to produce minutely patterned s of suitable materials over a substrate, such as a , to protect selected areas of it during subsequent , , or op ...
, 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 An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuit 200px, A circuit built on a printed circuit board (PCB). An electronic circuit is composed of indiv ...

integrated circuit
components, 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 Extreme may refer to: Science and mathematics Mathematics * Extreme point, a point in a convex set which does not lie in any open line segment joining two points in the set * Maxima and minima, extremes on a mathematical function Science * Extrem ...
.


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. 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 Mercury (element), Hg (mercury) or Iron, 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 (surface roughness, roughness and hydrophobicity) of polymer surfaces. For example, a poly(methyl methacrylate) surface can be smoothed by vacuum ultraviolet. UV radiation is useful in preparing low-surface-energy polymers for adhesives. Polymers exposed to UV will oxidize, thus raising the surface energy of the polymer. Once the surface energy of the polymer has been raised, the bond between the adhesive and the polymer is stronger.


Biology-related uses


Air purification

Using a Photocatalysis, catalytic chemical reaction from
titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical ...
and UVC exposure, oxidation of organic matter converts pathogens, pollens, and Mold (fungus), 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 formaldehyde, 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. 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 Volatile organic compound, VOCs. 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

Ultraviolet lamps are used to sterilization (microbiology), 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/RNA 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. 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. 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 has been researched for cheaply treating contaminated water using natural
sunlight Sunlight is a portion of the given off by the , in particular , , and light. On , sunlight is and through , and is obvious as when the Sun is above the . When direct is not blocked by s, it is experienced as sunshine, a combination of b ...

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 pasteurization, pasteurize fruit juices by flowing the juice over a high-intensity ultraviolet source. The effectiveness of such a process depends on the UV absorbance of the juice. Pulsed light (PL) is a technique of killing microorganisms on surfaces using pulses of an intense broad spectrum, rich in UV-C between 200 and 280 Nanometer, nm. Pulsed light works with xenon flash lamps that can produce flashes several times per second. Disinfection robots use pulsed UV.


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 Ultraviolet communication in butterflies, 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. 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. 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. 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 fauna, faunistic survey studies.


Therapy

Ultraviolet radiation is helpful in the treatment of skin conditions such as
psoriasis Psoriasis is a long-lasting, noncontagious autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. There are at least 80 types of autoimmune diseases. Nearly any body part c ...

psoriasis
and
vitiligo Vitiligo is a long-term skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic org ...

vitiligo
. Exposure to UVA, while the skin is hyper-photosensitive, by taking psoralens is an effective treatment for
psoriasis Psoriasis is a long-lasting, noncontagious autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. There are at least 80 types of autoimmune diseases. Nearly any body part c ...

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.


Herpetology

Reptiles need UVB for biosynthesis of vitamin D, and other metabolic processes. Specifically cholecalciferol (vitamin D3), which is needed for basic cellular / neural functioning as well as the utilization of calcium for bone and egg production. The UVA wavelength is also visible to many reptiles and might play a significant role in their ability survive in the wild as well as in visual communication between individuals. Therefore, in a typical reptile enclosure, a fluorescent UV a/b source (at the proper strength / spectrum for the species), must be 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 play important functions in the animals health. Natural sunlight in the right levels is always going to be superior to artificial sources, but this might not be possible for keepers in different parts of the world. It is a known 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 where blindness is the result of an improper UVa/b source use and placement
photokeratitis Photokeratitis or ultraviolet keratitis is a painful eye condition caused by exposure of insufficiently protected eyes to the ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength In physics Physi ...
. 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.


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.


See also

* Ultraviolet astronomy * High-energy visible light * Ultraviolet catastrophe * Ultraviolet index * UV stabilizers in plastics * Weather testing of polymers * UV marker * Infrared


References


Further reading

* * * *


External links

* * {{Authority control Electromagnetic radiation Electromagnetic spectrum Ultraviolet radiation