Ultraviolet (UV) is a form of
electromagnetic radiation
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) li ...
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 on the wave, such as two adjacent crests, t ...
from 10
nm (with a corresponding frequency around 30
PHz) to 400 nm (750
THz), shorter than that of
visible light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...
, but longer than
X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
s. UV radiation is present in
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 electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma; the plasma may produce visible light. An ...
s and specialized lights, such as
mercury-vapor lamp
A mercury-vapor lamp is a gas-discharge lamp that uses an electric arc through vaporized mercury to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger soda lime or borosilicate gl ...
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 used for indoor tanning. There are hundreds of differe ...
s, and
black lights. Although long-wavelength ultraviolet is not considered an
ionizing radiation because its
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they a ...
s lack the energy to
ionize
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule ...
atom
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons.
Every solid, liquid, gas, ...
s, it can cause
chemical reaction
A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
s and causes many substances to glow or
fluoresce
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...
. 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 and sterilizes surfaces with which it comes into contact. For humans,
suntan and
sunburn
Sunburn is a form of radiation burn that affects living tissue, such as skin, that results from an overexposure to ultraviolet (UV) radiation, usually from the Sun. Common symptoms in humans and animals include: red or reddish skin that is h ...
are familiar effects of exposure of the skin to UV light, along with an increased risk of
skin cancer
Skin cancers are cancers that arise from the skin. They are due to the development of abnormal cells that have the ability to invade or spread to other parts of the body. There are three main types of skin cancers: basal-cell skin cancer (BCC) ...
. 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 secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and many other biological effects. In humans, the most important compounds in this group are vitamin D3 (c ...
in most land
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...
s, 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 front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical ...
. Humans also lack
color receptor adaptations for ultraviolet rays. Nevertheless, the
photoreceptors of the
retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
are sensitive to near-UV, and people lacking a lens (a condition known as
aphakia
Aphakia is the absence of the lens of the eye, due to surgical removal, such as in cataract surgery, a perforating wound or ulcer, or congenital anomaly. It causes a loss of accommodation, high degree of farsightedness ( hyperopia), and a de ...
) 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 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 belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
''ultra'', "beyond"), violet being the color of the highest frequencies of
visible light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...
. Ultraviolet has a higher frequency (thus a shorter wavelength) than violet light.
UV radiation was discovered in 1801 when the German physicist
Johann Wilhelm Ritter observed that invisible rays just beyond the violet end of the visible spectrum darkened
silver chloride
Silver chloride is a chemical compound with the chemical formula Ag Cl. This white crystalline solid is well known for its low solubility in water (this behavior being reminiscent of the chlorides of Tl+ and Pb2+). Upon illumination or heating, ...
-soaked paper more quickly than violet light itself. He called them "(de-)oxidizing rays" (german: de-oxidierende Strahlen) to emphasize
chemical reactivity
In chemistry, reactivity is the impulse for which a chemical substance undergoes a chemical reaction, either by itself or with other materials, with an overall release of energy.
''Reactivity'' refers to:
* the chemical reactions of a single su ...
and to distinguish them from "
heat rays", discovered the previous year at the other end of the visible spectrum. The simpler term "chemical rays" was adopted soon afterwards, and remained popular throughout the 19th century, although some said that this radiation was entirely different from light (notably
John William Draper, who named them "tithonic rays"). 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 visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
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
Victor Schumann (21 December 1841 – 1 September 1913) was a physicist and spectroscopist who in 1893 discovered the vacuum ultraviolet.
Schumann wished to study the "Extreme Ultraviolet" region. For this, he used a prism and lenses in f ...
.
[The ozone layer also protects living beings from this.
]
Subtypes
The
electromagnetic spectrum
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging fro ...
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 development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Ar ...
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
photodiodes and
photocathode
A photocathode is a surface engineered to convert light ( photons) into electrons using the photoelectric effect. Photocathodes are important in accelerator physics where they are utilised in a photoinjector to generate high brightness electron ...
s, which can be tailored to be sensitive to different parts of the UV spectrum. Sensitive UV
photomultiplier A photomultiplier is a device that converts incident photons into an electrical signal.
Kinds of photomultiplier include:
* Photomultiplier tube, a vacuum tube converting incident photons into an electric signal. Photomultiplier tubes (PMTs for sh ...
s are available.
Spectrometer
A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...
s and
radiometers 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 with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
in the air, though the longer wavelengths around 150–200 nm can propagate through
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
. 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 equipment (for
semiconductor manufacturing
Semiconductor device fabrication is the process used to manufacture semiconductor devices, typically integrated circuit (IC) chips such as modern computer processors, microcontrollers, and memory chips such as NAND flash and DRAM that are pres ...
) and
circular dichroism spectrometers.
Technology for VUV instrumentation was largely driven by solar astronomy for many decades. While optics can be used to remove unwanted visible light that contaminates the VUV, in general; detectors can be limited by their response to non-VUV radiation, and the development of
solar-blind devices has been an important area of research. Wide-gap solid-state devices or vacuum devices with high-cutoff photocathodes can be attractive compared to silicon diodes.
Extreme UV (EUV or sometimes XUV) is characterized by a transition in the physics of interaction with matter. Wavelengths longer than about 30 nm interact mainly with the outer
valence electron
In chemistry and physics, a valence electron is an electron in the outer shell associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed. In a single covalent bond, a shared pair form ...
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 The angle of incidence, in geometric optics, is the angle between a ray incident on a surface and the line perpendicular (at 90 degree angle) to the surface at the point of incidence, called the normal. The ray can be formed by any waves, such as o ...
is possible. This technology was pioneered by the
NIXT
The NIXT, or Normal Incidence X-ray Telescope, was a sounding rocket payload flown in the 1990s by Professor Leon Golub of the Smithsonian Astrophysical Observatory, to prototype normal-incidence (conventional) optical designs in extreme ultrav ...
and
MSSTA 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 or Explorer 67) was a NASA space telescope for ultraviolet astronomy. EUVE was a part of NASA's Explorer spacecraft series. Launched on 7 June 1992. With instruments for ultraviolet (UV) radiation between ...
satellite
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioi ...
.
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 limit The Lyman limit is the short-wavelength end of the hydrogen Lyman series, at . It corresponds to the energy required for an electron in the hydrogen ground state to escape from the electric potential barrier that originally confined it, thus creatin ...
(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, manicures/ pedicures, non-permanent hair removal such ...
,
optoelectronic
Optoelectronics (or optronics) is the study and application of electronic devices and systems that find, detect and control light, usually considered a sub-field of photonics. In this context, ''light'' often includes invisible forms of radiat ...
, 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
![Ozone altitude UV graph](https://upload.wikimedia.org/wikipedia/commons/c/cb/Ozone_altitude_UV_graph.svg)
Very hot objects emit UV radiation (see
black-body radiation). The
Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
emits ultraviolet radiation at all wavelengths, including the extreme ultraviolet where it crosses into X-rays at 10 nm. Extremely hot
stars emit proportionally more UV radiation than the Sun.
Sunlight in space at the top of Earth's atmosphere (see
solar constant) is composed of about 50% infrared light, 40% visible light, and 10% ultraviolet light, for a total intensity of about 1400 W/m
2 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 19th-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 of th ...
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 when single oxygen atoms produced by UV
photolysis of dioxygen react with more dioxygen. The ozone layer is especially important in blocking most UVB and the remaining part of UVC not already blocked by ordinary oxygen in air.
Blockers, absorbers, and windows
Ultraviolet absorbers are molecules used in organic materials (
polymers
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...
,
paints
Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture. Paint can be made in many ...
, etc.) to absorb UV radiation to reduce the
UV degradation
In polymer chemistry photo-oxidation (sometimes: oxidative photodegradation) is the degradation of a polymer surface due to the combined action of light and oxygen. It is the most significant factor in the weathering of plastics. Photo-oxidatio ...
(photo-oxidation) of a material. The absorbers can themselves degrade over time, so monitoring of absorber levels in weathered materials is necessary.
In
sunscreen, ingredients that absorb UVA/UVB rays, such as
avobenzone
Avobenzone ( trade names Parsol 1789, Milestab 1789, Eusolex 9020, Escalol 517, Neo Heliopan 357 and others, INCI Butyl Methoxydibenzoylmethane) is an oil-soluble ingredient used in sunscreen products to absorb the full spectrum of UVA rays.
Hi ...
,
oxybenzone
Oxybenzone or benzophenone-3 or BP-3 (trade names Milestab 9, Eusolex 4360, Escalol 567, KAHSCREEN BZ-3) is an organic compound. It is a pale-yellow solid that is readily soluble in most organic solvents. Oxybenzone belongs to the class of aroma ...
and
octyl methoxycinnamate
Octyl methoxycinnamate or ethylhexyl methoxycinnamate ( INCI) or octinoxate (USAN), trade names Eusolex 2292 and Uvinul MC80, is an organic compound that is an ingredient in some sunscreens and lip balms. It is an ester formed from methoxycinna ...
, 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 coal and coal tar, vegetable matter, or petroleum products, including fuel oil, fluid ...
,
titanium dioxide
Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolub ...
, and
zinc oxide
Zinc oxide is an inorganic compound with the formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cement ...
.
For clothing, the
ultraviolet protection factor (UPF) represents the ratio of
sunburn
Sunburn is a form of radiation burn that affects living tissue, such as skin, that results from an overexposure to ultraviolet (UV) radiation, usually from the Sun. Common symptoms in humans and animals include: red or reddish skin that is h ...
-causing UV without and with the protection of the fabric, similar to
sun protection factor (SPF) ratings for
sunscreen. 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
, owners =
, headquarters = Paris, Île-de-France, France
, coordinates =
, spaceport = Guiana Space Centre
, seal = File:ESA emblem seal.png
, seal_size = 130px
, image = Views in the Main Control Room (120 ...
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 (optics), the physical property of allowing the transmission of light through a material
They may also refer to:
Literal uses
* Transparency (photography), a still, ...
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:
** In lingu ...
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 consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses in which other ingredients are added which change ...
, depending on quality, can be transparent even to
vacuum UV
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
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 tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
and some crystals such as CaF
2 and MgF
2 transmit well down to 150 nm or 160 nm wavelengths.
Wood's glass
Wood's glass is an optical filter glass invented in 1903 by American physicist Robert Williams Wood (1868–1955), which allows ultraviolet and infrared light
Infrared (IR), sometimes called infrared light, is electromagnetic radiation ...
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
Nickel (III) oxide is the inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydr ...
developed during
World War I
World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
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
A mercury-vapor lamp is a gas-discharge lamp that uses an electric arc through vaporized Mercury (element), mercury to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger Soda–lime g ...
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
A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet ligh ...
, but use a
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
Wood's glass is an optical filter glass invented in 1903 by American physicist Robert Williams Wood (1868–1955), which allows ultraviolet and infrared light
Infrared (IR), sometimes called infrared light, is electromagnetic radiation ...
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
Wood's glass is an optical filter glass invented in 1903 by American physicist Robert Williams Wood (1868–1955), which allows ultraviolet and infrared light
Infrared (IR), sometimes called infrared light, is electromagnetic radiation ...
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 by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...
'', 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 used for indoor tanning. There are hundreds of differe ...
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 gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet ligh ...
tube with no phosphor coating, composed of
fused quartz
Fused quartz, fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses in which other ingredients are added which change ...
or
vycor, since ordinary glass absorbs UV‑C. These lamps emit ultraviolet light with two peaks in the UV‑C band at 253.7 nm and 185 nm due to the
mercury within the lamp, as well as some visible light. From 85% to 90% of the UV produced by these lamps is at 253.7 nm, whereas only 5–10% is at 185 nm. 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 lamps are also made from an incandescent light bulb with a filter coating which absorbs most visible light.
Halogen lamps
A halogen lamp (also called tungsten halogen, quartz-halogen, and quartz iodine lamp) is an incandescent lamp consisting of a tungsten filament sealed in a compact transparent envelope that is filled with a mixture of an inert gas and a smal ...
with
fused quartz
Fused quartz, fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses in which other ingredients are added which change ...
envelopes are used as inexpensive UV light sources in the near UV range, from 400 to 300 nm, in some scientific instruments. Due to its
black-body spectrum a filament light bulb is a very inefficient ultraviolet source, emitting only a fraction of a percent of its energy as UV.
Gas-discharge lamps
Specialized UV
gas-discharge lamps containing different gases produce UV radiation at particular spectral lines for scientific purposes.
Argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...
and
deuterium arc lamp
A deuterium arc lamp (or simply deuterium lamp) is a low-pressure gas-discharge light source often used in spectroscopy when a continuous spectrum in the ultraviolet region is needed.
Plasma "arc" or discharge lamps using hydrogen are notable ...
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 formula MgF2. The compound is a white crystalline salt and is transparent over a wide range of wavelengths, with commercial uses in optics that are also used in space telescopes. It occurs natur ...
. 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
A xenon arc lamp is a highly specialized type of gas discharge lamp, an electric light that produces light by passing electricity through ionized xenon gas at high pressure. It produces a bright white light to simulate sunlight, with application ...
(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 when a continuous spectrum in the ultraviolet region is needed.
Plasma "arc" or discharge lamps using hydrogen are notable ...
s,
mercury-xenon arc lamps, and
metal-halide arc lamps.
The
excimer lamp
An excimer lamp (or excilamp) is a source of ultraviolet light based on spontaneous emission of excimer (exciplex) molecules.
Introduction
Excimer lamps are quasimonochromatic light sources operating over a wide range of wavelengths in the ult ...
, 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 device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (cor ...
(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 are in 395 nm and 365 nm wavelengths, both of which are in the UV‑A spectrum. The rated wavelength is the peak wavelength that the LEDs put out, but light at both higher and lower wavelengths are present.
The cheaper and more common 395 nm UV LEDs are much closer to the visible spectrum, and give off a purple color. Other UV LEDs deeper into the spectrum do not emit as much visible light LEDs are used for applications such as
UV curing
UV curing (ultraviolet curing) is the process by which ultraviolet light is used to initiate a photochemical reaction that generates a crosslinked network of polymers. UV curing is adaptable to printing, coating, decorating, stereolithography, ...
applications, charging glow-in-the-dark objects such as paintings or toys, and lights for detecting counterfeit money and bodily fluids. UV LEDs are also used in digital print applications and inert UV curing environments. Power densities approaching 3 W/cm
2 (30 kW/m
2) 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 (also known as disinfection lamp or sterilizer 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 lead ...
s.
[
] Also, they are used as line sources to replace
deuterium lamps in
liquid chromatography
In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it through a system (a ...
instruments.
Ultraviolet lasers
Gas laser
A gas laser is a laser in which an electric current is discharged through a gas to produce coherent light. The gas laser was the first continuous-light laser and the first laser to operate on the principle of converting electrical energy to a lase ...
s,
laser diode
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 device similar to a light-emitting diode in which a diode pumped directly with e ...
s, and
solid-state laser
A solid-state laser is a laser that uses a 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 separate class ...
s can be manufactured to emit ultraviolet rays, and lasers are available that cover the entire UV range. The
nitrogen gas laser uses electronic excitation of nitrogen molecules to emit a beam that is mostly UV. The strongest ultraviolet lines are at 337.1 nm and 357.6 nm in wavelength. Another type of high-power gas lasers are
excimer lasers. 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 production by
photolithography. The current wavelength limit of production of coherent UV is about 126 nm, characteristic of the Ar
2* 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 with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 ...
-
doped lithium strontium aluminum fluoride crystals (Ce:LiSAF), a process developed in the 1990s at
Lawrence Livermore National Laboratory.
[
] Wavelengths shorter than 325 nm are commercially generated in
diode-pumped solid-state laser
A diode-pumped solid-state laser (DPSSL) is a solid-state laser made by pumping a solid gain medium, for example, a ruby or a neodymium-doped YAG crystal, with a laser diode.
DPSSLs have advantages in compactness and efficiency over other types ...
s. Ultraviolet lasers can also be made by applying
frequency conversion to lower-frequency lasers.
Ultraviolet lasers have applications in industry (
laser engraving), medicine (
dermatology
Dermatology is the branch of medicine dealing with the skin.''Random House Webster's Unabridged Dictionary.'' Random House, Inc. 2001. Page 537. . It is a speciality with both medical and surgical aspects. A dermatologist is a specialist medica ...
, and
keratectomy), chemistry (
MALDI
In mass spectrometry, matrix-assisted laser desorption/ionization (MALDI) is an ionization technique that uses a laser energy absorbing matrix to create ions from large molecules with minimal fragmentation. It has been applied to the analysis of b ...
),
free-air secure communications, computing (
optical storage
IBM defines optical storage as "any storage method that uses a laser to store and retrieve data from optical media." '' Britannica'' notes that it "uses low-power laser beams to record and retrieve digital (binary) data." Compact disc (CD) an ...
), 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. 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 ...
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 has implications for the risks and benefits of sun exposure and is also implicated in issues such as fluorescent lamps and health
Fluorescent lamps have been suggested to affect human health in various ways.
Flicker effects
New lighting systems have not used magnetic ballasts since the turn of the century, however some older installations still remain. Fluorescent lamps with ...
. 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 secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and many other biological effects. In humans, the most important compounds in this group are vitamin D3 (c ...
, 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. 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 characterized by raised areas of abnormal skin. These areas are red, pink, or purple, dry, itchy, and scaly. Psoriasis varies in severity from small, localized patches to complete ...
, eczema
Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can ...
, jaundice, vitiligo
Vitiligo is a disorder that causes the skin to lose its color. Specific causes are unknown but studies suggest a link to immune system changes.
Signs and symptoms
The only sign of vitiligo is the presence of pale patchy areas of depigmen ...
, atopic dermatitis, and localized scleroderma
Scleroderma is a group of autoimmune diseases that may result in changes to the 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 areas ...
. 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) and some of its organelles, and sub ...
arrest in keratinocytes
Keratinocytes are the primary type of cell found in the epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells.
Basal cells in the basal layer (''stratum basale'') of the skin are sometimes referre ...
, 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 of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
. 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 datum and a point or object. The exact definition and reference datum varies according to the context ...
s and people living in high latitude
In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...
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 celestial sphere. "Above" means in the vertical direction ( plumb line) opposite to the gravity direction at that location ( nadir). The zenith is the "high ...
are low, are particularly at risk. Skin, the circadian 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 cancer cells and objects such as wood splint ...
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 (UV) rays from either natural (e.g. intense sunlight) or artificial (e.g. the electric arc during welding) ...
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
Who or WHO may refer to:
* Who (pronoun), an interrogative or relative pronoun
* Who?, one of the Five Ws in journalism
* World Health Organization
Arts and entertainment Fictional characters
* Who, a creature in the Dr. Seuss book '' Horton He ...
-standard ultraviolet index
The ultraviolet index, or UV index, is an international standard measurement of the strength of the sunburn-producing ultraviolet (UV) radiation at a particular place and time. It is primarily used in daily and hourly forecasts aimed at the general ...
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 that affects living tissue, such as skin, that results from an overexposure to ultraviolet (UV) radiation, usually from the Sun. Common symptoms in humans and animals include: red or reddish skin that is h ...
but also some forms of skin cancer
Skin cancers are cancers that arise from the skin. They are due to the development of abnormal cells that have the ability to invade or spread to other parts of the body. There are three main types of skin cancers: basal-cell skin cancer (BCC) ...
. 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 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 and the ozone hole.
The most deadly form of skin cancer
Skin cancers are cancers that arise from the skin. They are due to the development of abnormal cells that have the ability to invade or spread to other parts of the body. There are three main types of skin cancers: basal-cell skin cancer (BCC) ...
, malignant 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
Indirect, the opposite of direct, may refer to:
* Indirect approach, a battle strategy
* Indirect DNA damage, caused by UV-photons
*Indirect agonist or indirect-acting agonist, a substance that enhances the release or action of an endogenous neurot ...
(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 dimer
Pyrimidine dimers are molecular lesions formed from thymine or cytosine bases in DNA via photochemical reactions, commonly associated with direct DNA damage. Ultraviolet light (UV; particularly UVB) induces the formation of covalent linkages bet ...
s or cytosine dimers 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 excites DNA molecules in skin cells, causing aberrant covalent bonds to form between adjacent pyrimidine bases, producing a dimer
Dimer may refer to:
* Dimer (chemistry), a chemical structure formed from two similar sub-units
** Protein dimer, a protein quaternary structure
** d-dimer
* Dimer model, an item in statistical mechanics, based on ''domino tiling''
* Julius 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
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA replication, DNA or viral repl ...
.
As a defense against UV radiation, the amount of the brown pigment melanin
Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...
in the skin increases when exposed to moderate (depending on skin type) levels of radiation; this is commonly known as a sun tan. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, protecting the skin against both direct and indirect DNA damage
Indirect, the opposite of direct, may refer to:
* Indirect approach, a battle strategy
* Indirect DNA damage, caused by UV-photons
*Indirect agonist or indirect-acting agonist, a substance that enhances the release or action of an endogenous neurot ...
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
Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...
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. Five sunscreen ingredients have been shown to protect mice against skin tumors. However, some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells. 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 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 with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolub ...
, zinc oxide
Zinc oxide is an inorganic compound with the formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cement ...
, and avobenzone
Avobenzone ( trade names Parsol 1789, Milestab 1789, Eusolex 9020, Escalol 517, Neo Heliopan 357 and others, INCI Butyl Methoxydibenzoylmethane) is an oil-soluble ingredient used in sunscreen products to absorb the full spectrum of UVA rays.
Hi ...
, which help protect against UV‑A rays.
The photochemical properties of melanin make it an excellent photoprotectant. However, sunscreen chemicals cannot dissipate the energy of the excited state as efficiently as melanin and therefore, if sunscreen ingredients penetrate into the lower layers of the skin, the amount of reactive oxygen species
In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen.
The reduction of molecular oxygen () p ...
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
In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen.
The reduction of molecular oxygen () p ...
(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
Rosacea is a long-term skin condition that typically affects the face. It results in redness, pimples, swelling, and small and superficial dilated blood vessels. Often, the nose, cheeks, forehead, and chin are most involved. A red, enlarg ...
, dermatomyositis
Dermatomyositis (DM) is a long-term inflammatory disorder which affects skin and the muscles. Its symptoms are generally a skin rash and worsening muscle weakness over time. These may occur suddenly or develop over months. Other symptoms may inc ...
, Darier's disease
Darier's disease (DAR) is an inherited skin disorder that presents with multiple greasy, crusting, thick brown bumps that merge into patches.
It is an autosomal dominant disorder discovered by French dermatologist Ferdinand-Jean Darier. Darier's ...
, 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 (UV) rays from either natural (e.g. intense sunlight) or artificial (e.g. the electric arc during welding) ...
) and can lead to cataract
A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around light, trouble ...
s, pterygium
Pterygium (plural ''pterygia'' or ''pterygiums'') refers to any wing-like triangular membrane occurring in the neck, eyes, knees, elbows, ankles or digits.
The term comes from the Greek word ''pterygion'' meaning "wing".
Types
* Popliteal pter ...
and pinguecula
A pinguecula is a common type of conjunctival stromal degeneration in the eye. It appears as an elevated yellow-white plaque in the bulbar conjunctiva near the limbus. Calcification may also seen occasionally.
Etiology
The exact etiology is unk ...
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 front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical ...
, the lens
A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...
, and the retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
can be damaged.
Protective eyewear
Eye protection is protective gear for the eyes, and sometimes face, designed to reduce the risk of injury. Examples of risks requiring eye protection can include: impact from particles or debris, light or radiation, wind blast, heat, sea s ...
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
Glasses, also known as eyeglasses or spectacles, are vision eyewear, with lenses (clear or tinted) mounted in a frame that holds them in front of a person's eyes, typically utilizing a bridge over the nose and hinged arms (known as temples or ...
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 photodegradation) is the degradation of a polymer surface due to the combined action of light and oxygen. It is the most significant factor in the weathering of plastics. Photo-oxidatio ...
is one form of polymer degradation
Polymer degradation is the reduction in the physical properties of a polymer, such as strength, caused by changes in its chemical composition. Polymers and particularly plastics are subject to degradation at all stages of their product life cycl ...
that affects plastics exposed to sunlight. The problem appears as discoloration or fading, cracking, loss of strength or disintegration. The effects of attack increase with exposure time and sunlight intensity. The addition of UV absorbers inhibits the effect.
Sensitive polymers include thermoplastic
A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
Most thermoplastics have a high molecular weight. The polymer chains associate ...
s and speciality fibers like aramid
Aramid fibers, short for aromatic polyamide, are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic-rated body armor fabric and ballistic composites, in marine cordage, ma ...
s. 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
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compoun ...
and dyes absorb UV and change colour, so paintings
Painting is the practice of applying paint, pigment, color or other medium to a solid surface (called the "matrix" or "support"). The medium is commonly applied to the base with a brush, but other implements, such as knives, sponges, and ai ...
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 painting
Watercolor (American English) or watercolour (British English; see spelling differences), also ''aquarelle'' (; from Italian diminutive of Latin ''aqua'' "water"), is a painting method”Watercolor may be as old as art itself, going back to ...
s 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 by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...
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
Photoionization is the physical process in which an ion is formed from the interaction of a photon with an atom or molecule.
Cross section
Not every interaction between a photon and an atom, or molecule, will result in photoionization. The prob ...
, ultraviolet photoelectron spectroscopy
Ultraviolet photoelectron spectroscopy (UPS) refers to the measurement of kinetic energy spectra of photoelectrons emitted by molecules which have absorbed ultraviolet photons, in order to determine molecular orbital energies in the valence regio ...
, standard integrated circuit manufacture by photolithography
* ''230–365 nm'': UV-ID, label tracking, barcode
A barcode or bar code is a method of representing data in a visual, machine-readable form. Initially, barcodes represented data by varying the widths, spacings and sizes of parallel lines. These barcodes, now commonly referred to as linear or o ...
s
* ''230–400 nm'': Optical sensors, various instrumentation
* ''240–280 nm'': Disinfection
A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than st ...
, decontamination of surfaces and water ( DNA absorption has a peak at 260 nm), germicidal lamp
A germicidal lamp (also known as disinfection lamp or sterilizer 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 lead ...
s
* ''200–400 nm'': Forensic analysis
Forensic science, also known as criminalistics, is the application of science to criminal and civil laws, mainly—on the criminal side—during criminal investigation, as governed by the legal standards of admissible evidence and criminal p ...
, drug detection
* ''270–360 nm'': Protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
analysis, DNA sequencing, drug discovery
* ''280–400 nm'': Medical imaging of cells
* ''300–320 nm'': Light therapy
Light therapy, also called phototherapy or bright light therapy is intentional daily exposure to direct sunlight or similar-intensity artificial light in order to treat medical disorders, especially seasonal affective disorder (SAD) and circad ...
in medicine
* ''300–365 nm'': Curing of polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
s and printer ink
An ink cartridge or inkjet cartridge is a component of an inkjet printer that contains the ink that is deposited onto paper during printing.
Each ink cartridge contains one or more ink reservoirs; certain producers also add electronic contact ...
s
* ''350–370 nm'': Bug zapper
A bug zapper, more formally called an electrical discharge insect control system, electric insect killer or (insect) electrocutor trap, is a device that attracts and kills flying insects that are attracted by light. A light source attracts insect ...
s (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
Ultraviolet astronomy is the observation of electromagnetic radiation at ultraviolet wavelengths between approximately 10 and 320 nanometres; shorter wavelengths—higher energy photons—are studied by X-ray astronomy and gamma-ray astr ...
, 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
A corona discharge is an electrical discharge caused by the ionization of a fluid such as air surrounding a conductor (material), conductor carrying a high voltage. It represents a local region where the air (or other fluid) has undergone e ...
on electrical apparatus can be detected by its ultraviolet emissions. Corona causes degradation of electrical insulation and emission of ozone
Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
and nitrogen oxide.
EPROM
An EPROM (rarely EROM), or erasable programmable read-only memory, is a type of programmable read-only memory (PROM) chip that retains its data when its power supply is switched off. Computer memory that can retrieve stored data after a power s ...
s (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 tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
) window on the top of the chip that allows the UV radiation in.
Fluorescent dye uses
Colorless fluorescent dyes
A fluorophore (or fluorochrome, similarly to a chromophore) is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with sev ...
that emit blue light under UV are added as optical brightener
Optical brighteners, optical brightening agents (OBAs), fluorescent brightening agents (FBAs), or fluorescent whitening agents (FWAs), are chemical compounds that absorb light in the ultraviolet and violet region (usually 340-370 nm) of the ...
s 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 paint
Black light paint or black light fluorescent paint is luminous paint that glows under a black light. It is based on pigments that respond to light in the ultraviolet segment of the electromagnetic spectrum. The paint may or may not be colorful ...
s 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
A passport is an official travel document issued by a government that contains a person's identity. A person with a passport can travel to and from foreign countries more easily and access consular assistance. A passport certifies the personal ...
, the paper may include a UV watermark
A watermark is an identifying image or pattern in paper that appears as various shades of lightness/darkness when viewed by transmitted light (or when viewed by reflected light, atop a dark background), caused by thickness or density variations ...
or fluorescent multicolor fibers that are visible under ultraviolet light. Postage stamps are tagged Tagged may refer to:
* Tagged (website), a social discovery website
* Tagged (web series), an American teen psychological thriller web series
{{disambiguation ...
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
Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...
and forensics). Some brands of pepper spray
Pepper spray, oleoresin capsicum spray, OC spray, capsaicin spray, or capsicum spray is a lachrymatory agent (a compound that irritates the eyes to cause a burning sensation, pain, and temporary blindness) used in policing, riot control, ...
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 inspection) or they may be bound to ferrite particles caught in magnetic leakage fields in ferrous materials ( magnetic particle inspection).
Analytic uses
Forensics
UV is an investigative tool at the crime scene helpful in locating and identifying bodily fluids such as semen, blood, and saliva. 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 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
Papyrus ( ) is a material similar to thick paper that was used in ancient times as a writing surface. It was made from the pith of the papyrus plant, '' Cyperus papyrus'', a wetland sedge. ''Papyrus'' (plural: ''papyri'') can also refer to a ...
, such as the burned papyri of the Villa of the Papyri
The Villa of the Papyri ( it, Villa dei Papiri, also known as ''Villa dei Pisoni'' and in early excavation records as the ''Villa Suburbana'') was an ancient Roman villa in Herculaneum, in what is now Ercolano, southern Italy. It is named afte ...
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
Ink is a gel, sol, or solution that contains at least one colorant, such as a dye or pigment, and is used to color a surface to produce an image, text, or design. Ink is used for drawing or writing with a pen, brush, reed pen, or quill. Thicker ...
on vellum
Vellum is prepared animal skin or membrane, typically used as writing material. Parchment is another term for this material, from which vellum is sometimes distinguished, when it is made from calfskin, as opposed to that made from other anima ...
.
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 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
A chemical structure determination includes a chemist's specifying the molecular geometry and, when feasible and necessary, the electronic structure of the target molecule or other solid. Molecular geometry refers to the spatial arrangement of ...
, 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 A spectrofluorometer is an instrument which takes advantage of fluorescent properties of some compounds in order to provide information regarding their concentration and chemical environment in a sample. A certain excitation wavelength is selected, ...
. In biological research, UV radiation is used for quantification of nucleic acids or protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s. In environmental chemistry, UV radiation could also be used to detect Contaminants of emerging concern
Contaminants of emerging concern (CECs) is a term used by water quality professionals to describe pollutants that have been detected in environmental monitoring samples, that may cause ecological or human health impacts, and typically are not regul ...
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 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
Raman scattering or the Raman effect () is the inelastic scattering of photons by matter, meaning that there is both an exchange of energy and a change in the light's direction. Typically this effect involves vibrational energy being gained by a ...
in water.
Ultraviolet lamps are also used as part of the analysis of some mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
s and gems
Gems, or gemstones, are polished, cut stones or minerals.
Gems or GEMS may also refer to:
Arts, entertainment and media
* ''Gems'' (Aerosmith album), 1988
* ''Gems'' (Patti LaBelle album), 1994
* ''Gems'' (Michael Bolton album), 2011
* Gems TV, ...
.
Material science uses
Fire detection
In general, ultraviolet detectors use either a solid-state device, such as one based on silicon carbide
Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal s ...
or aluminium nitride, or a gas-filled tube as the sensing element. UV detectors that are sensitive to UV in any part of the spectrum respond to irradiation by sunlight and artificial light
Lighting or illumination is the deliberate use of light to achieve practical or aesthetic effects. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing daylig ...
. A burning hydrogen flame, for instance, radiates strongly in the 185- to 260-nanometer range and only very weakly in the IR region, whereas a coal fire emits very weakly in the UV band yet very strongly at IR wavelengths; thus, a fire detector that operates using both UV and IR detectors is more reliable than one with a UV detector alone. Virtually all fires emit some radiation in the UVC band, whereas the Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
's radiation at this band is absorbed by the Earth's atmosphere
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing fo ...
. 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 hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
s, metals, sulfur, hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
, hydrazine, and ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
. Arc welding
Arc welding is a welding process that is used to join metal to metal by using electricity to create enough heat to melt metal, and the melted metals, when cool, result in a binding of the metals. It is a type of welding that uses a welding powe ...
, electrical arcs, lightning
Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an avera ...
, X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
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, 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 semiconductor
A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...
s, 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.
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
In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...
occurs, and so the adhesives harden or cure, usually within a few seconds. Applications include glass and plastic bonding, optical fiber
An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass ( silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a mea ...
coatings, the coating of flooring, UV coating and paper finishes in offset printing
Printing is a process for mass reproducing text and images using a master form or template. The earliest non-paper products involving printing include cylinder seals and objects such as the Cyrus Cylinder and the Cylinders of Nabonidus. The ...
, dental fillings, and decorative fingernail "gels".
UV sources for UV curing applications include UV lamps, UV LEDs, and excimer
An excimer (originally short for excited dimer) is a short-lived dimeric or heterodimeric molecule formed from two species, at least one of which has a valence shell completely filled with electrons (for example, noble gases). In this case, form ...
flash lamps. Fast processes such as flexo or offset printing require high-intensity light focused via reflectors onto a moving substrate and medium so high-pressure Hg (mercury) or Fe (iron, doped)-based bulbs are used, energized with electric arcs or microwaves. Lower-power fluorescent lamps and LEDs can be used for static applications. Small high-pressure lamps can have light focused and transmitted to the work area via liquid-filled or fiber-optic light guides.
The impact of UV on polymers is used for modification of the ( roughness and hydrophobicity
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, t ...
) 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 polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
s 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 catalytic chemical reaction from titanium dioxide
Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolub ...
and UVC exposure, oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
of organic matter converts pathogens
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...
, pollens
Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gameto ...
, and mold
A mold () or mould () is one of the structures certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. Not ...
spores
In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...
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
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
and VOCs
Volatile organic compounds (VOCs) are organic compounds that have a high vapour pressure at room temperature. High vapor pressure correlates with a low boiling point, which relates to the number of the sample's molecules in the surrounding air, a ...
. UV lamps radiating at 184 and 254 nm can remove low concentrations of hydrocarbons
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or e ...
and carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
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 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
A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than st ...
using UV radiation is commonly used in wastewater
Wastewater is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of domestic, industrial ...
treatment applications and is finding an increased usage in municipal drinking water treatment
Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, inc ...
. Many bottlers of spring water use UV disinfection equipment to sterilize their water. Solar water disinfection
Solar water disinfection, in short SODIS, is a type of portable water purification that uses solar energy to make biologically-contaminated (e.g. bacteria, viruses, protozoa and worms) water safe to drink. Water contaminated with non-biological age ...
has been researched for cheaply treating contaminated water using natural sunlight. The UV-A irradiation and increased water temperature kill organisms in the water.
Ultraviolet radiation is used in several food processes to kill unwanted microorganisms. UV can be used to pasteurize
Pasteurization or pasteurisation is a process of food preservation in which packaged and non-packaged foods (such as milk and fruit juices) are treated with mild heat, usually to less than , to eliminate pathogens and extend shelf life. ...
fruit juices by flowing the juice over a high-intensity ultraviolet source. The effectiveness of such a process depends on the UV absorbance
Absorbance is defined as "the logarithm of the ratio of incident to transmitted radiant power through a sample (excluding the effects on cell walls)". Alternatively, for samples which scatter light, absorbance may be defined as "the negative lo ...
of the juice.
Pulsed light (PL) is a technique of killing microorganisms on surfaces using pulses of an intense broad spectrum, rich in UV-C between 200 and 280 nm. Pulsed light works with xenon flash lamp
A flashtube (flashlamp) is an electric arc lamp designed to produce extremely intense, incoherent, full-spectrum white light for a very short time. A flashtube is a glass tube with an electrode at each end and is filled with a gas that, when tr ...
s 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 communication system
A communications system or communication system is a collection of individual telecommunications networks, transmission systems, relay stations, tributary stations, and terminal equipment usually capable of interconnection and interoperat ...
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
The green-veined white (''Pieris napi'') is a butterfly of the family Pieridae.
Appearance and distribution
A circumboreal species widespread across Europe and Asia, including the Indian subcontinent, Japan, the Maghreb and North America. It is ...
'' 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
Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar wor ...
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 zapper
A bug zapper, more formally called an electrical discharge insect control system, electric insect killer or (insect) electrocutor trap, is a device that attracts and kills flying insects that are attracted by light. A light source attracts insect ...
s 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
Entomology () is the scientific study of insects, a branch of zoology. In the past the term "insect" was less specific, and historically the definition of entomology would also include the study of animals in other arthropod groups, such as arach ...
for collecting
The hobby of collecting includes seeking, locating, acquiring, organizing, cataloging, displaying, storing, and maintaining items that are of interest to an individual ''collector''. Collections differ in a wide variety of respects, most obvi ...
nocturnal insects during 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 characterized by raised areas of abnormal skin. These areas are red, pink, or purple, dry, itchy, and scaly. Psoriasis varies in severity from small, localized patches to complete ...
and vitiligo
Vitiligo is a disorder that causes the skin to lose its color. Specific causes are unknown but studies suggest a link to immune system changes.
Signs and symptoms
The only sign of vitiligo is the presence of pale patchy areas of depigmen ...
. Exposure to UVA, while the skin is hyper-photosensitive, by taking psoralen
Psoralen (also called psoralene) is the parent compound in a family of naturally occurring organic compounds known as the linear furanocoumarins. It is structurally related to coumarin by the addition of a fused furan ring, and may be considered ...
s is an effective treatment for psoriasis
Psoriasis is a long-lasting, noncontagious autoimmune disease characterized by raised areas of abnormal skin. These areas are red, pink, or purple, dry, itchy, and scaly. Psoriasis varies in severity from small, localized patches to complete ...
. Due to the potential of psoralens to cause damage to the liver
The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...
, PUVA therapy
PUVA (psoralen and UVA) is an ultraviolet light therapy treatment for skin diseases: eczema, psoriasis, graft-versus-host disease, vitiligo, mycosis fungoides, large plaque parapsoriasis, and cutaneous T-cell lymphoma, using the sensitizing ef ...
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
Vitamin A is a fat-soluble vitamin and an essential nutrient for humans. It is a group of organic compounds that includes retinol, retinal (also known as retinaldehyde), retinoic acid, and several provitamin A carotenoids (most notably ...
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
Cholecalciferol, also known as vitamin D3 and colecalciferol, is a type of vitamin D that is made by the skin when exposed to sunlight; it is found in some foods and can be taken as a dietary supplement.
Cholecalciferol is made in the skin fo ...
(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
Cholecalciferol, also known as vitamin D3 and colecalciferol, is a type of vitamin D that is made by the skin when exposed to sunlight; it is found in some foods and can be taken as a dietary supplement.
Cholecalciferol is made in the skin fo ...
(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 (UV) rays from either natural (e.g. intense sunlight) or artificial (e.g. the electric arc during welding) ...
. 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
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
to ultraviolet radiation. UVB causes thymine
Thymine () ( symbol T or Thy) is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidi ...
base pairs next to each other in genetic sequences to bond together into thymine dimers
Pyrimidine dimers are molecular lesions formed from thymine or cytosine bases in DNA via photochemical reactions, commonly associated with direct DNA damage. Ultraviolet light (UV; particularly UVB) induces the formation of covalent linkages bet ...
, 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 prokaryote
A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Conne ...
s 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 dimer
Pyrimidine dimers are molecular lesions formed from thymine or cytosine bases in DNA via photochemical reactions, commonly associated with direct DNA damage. Ultraviolet light (UV; particularly UVB) induces the formation of covalent linkages bet ...
s by nucleotide excision repair enzymes. Many enzymes and proteins involved in modern mitosis and meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately r ...
are similar to repair enzymes, and are believed to be evolved modifications of the enzymes originally used to overcome DNA damages caused by UV.
Photobiology
Photobiology is the scientific study of the beneficial and harmful interactions of non-ionizing radiation in living organisms, conventionally demarcated around 10 eV, the first ionization energy of oxygen. UV ranges roughly from 3 to 30 eV in energy. Hence photobiology entertains some, but not all, of the UV spectrum.
See also
* High-energy visible light
High-energy visible light (HEV light) is high-frequency, high-energy light in the violet/blue band from 400 to 450 nm in the visible spectrum,
which has a number of biological effects, including those on the eye.
HEV light may be a cause ...
* Infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
* Ultraviolet astronomy
Ultraviolet astronomy is the observation of electromagnetic radiation at ultraviolet wavelengths between approximately 10 and 320 nanometres; shorter wavelengths—higher energy photons—are studied by X-ray astronomy and gamma-ray astr ...
* Ultraviolet catastrophe
The ultraviolet catastrophe, also called the Rayleigh–Jeans catastrophe, was the prediction of late 19th century/early 20th century classical physics that an ideal black body at thermal equilibrium would emit an unbounded quantity of energy ...
* Ultraviolet index
The ultraviolet index, or UV index, is an international standard measurement of the strength of the sunburn-producing ultraviolet (UV) radiation at a particular place and time. It is primarily used in daily and hourly forecasts aimed at the general ...
* UV marker
An ultraviolet (UV) marker is a pen whose marks are fluorescent but transparent: the marks can be seen only under an ultraviolet light. They are commonly used in security situations to identify belongings or to prevent the reproduction of unautho ...
* UV stabilizers in plastics
* Weather testing of polymers
Accelerated photo-ageing of polymers in SEPAP units is the controlled polymer degradation and polymer coating degradation under lab or natural conditions.
The prediction of the ageing of plastic materials is an important subject that concerns ...
References
Further reading
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External links
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{{Authority control
Electromagnetic radiation
Electromagnetic spectrum
Ultraviolet radiation