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114-660: Ultraviolet radiation , also known as simply UV , is electromagnetic radiation of wavelengths of 10–400 nanometers , shorter than that of visible light , but longer than X-rays . 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 arcs , Cherenkov radiation , and specialized lights, such as mercury-vapor lamps , tanning lamps , and black lights . The photons of ultraviolet have greater energy than those of visible light, from about 3.1 to 12  electron volts , around

228-435: A magnetic-dipole –type that dies out with distance from the current. In a similar manner, moving charges pushed apart in a conductor by a changing electrical potential (such as in an antenna) produce an electric-dipole –type electrical field, but this also declines with distance. These fields make up the near field. Neither of these behaviours is responsible for EM radiation. Instead, they only efficiently transfer energy to

342-422: A microwave oven . These interactions produce either electric currents or heat, or both. Like radio and microwave, infrared (IR) also is reflected by metals (and also most EMR, well into the ultraviolet range). However, unlike lower-frequency radio and microwave radiation, Infrared EMR commonly interacts with dipoles present in single molecules, which change as atoms vibrate at the ends of a single chemical bond. It

456-461: A transverse wave , where the electric field E and the magnetic field B are both perpendicular to the direction of wave propagation. The electric and magnetic parts of the field in an electromagnetic wave stand in a fixed ratio of strengths to satisfy the two Maxwell equations that specify how one is produced from the other. In dissipation-less (lossless) media, these E and B fields are also in phase, with both reaching maxima and minima at

570-611: A wave form of the electric and magnetic equations , thus uncovering the wave-like nature of electric and magnetic fields and their symmetry . Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light , Maxwell concluded that light itself is an EM wave. Maxwell's equations were confirmed by Heinrich Hertz through experiments with radio waves. Maxwell's equations established that some charges and currents ( sources ) produce local electromagnetic fields near them that do not radiate. Currents directly produce magnetic fields, but such fields of

684-436: A boundary of 190 nm between hard and soft UV regions. Very hot objects emit UV radiation (see black-body radiation ). The Sun emits ultraviolet radiation at all wavelengths, including the extreme ultraviolet where it crosses into X-rays at 10 nm. Extremely hot stars (such as O- and B-type) emit proportionally more UV radiation than the Sun. Sunlight in space at the top of Earth's atmosphere (see solar constant )

798-581: A bulk collection of charges which are spread out over large numbers of affected atoms. In electrical conductors , such induced bulk movement of charges ( electric currents ) results in absorption of the EMR, or else separations of charges that cause generation of new EMR (effective reflection of the EMR). An example is absorption or emission of radio waves by antennas, or absorption of microwaves by water or other molecules with an electric dipole moment, as for example inside

912-411: A certain minimum frequency, which depended on the particular metal, no current would flow regardless of the intensity. These observations appeared to contradict the wave theory, and for years physicists tried in vain to find an explanation. In 1905, Einstein explained this puzzle by resurrecting the particle theory of light to explain the observed effect. Because of the preponderance of evidence in favor of

1026-605: A component wave is said to be monochromatic . A monochromatic electromagnetic wave can be characterized by its frequency or wavelength, its peak amplitude, its phase relative to some reference phase, its direction of propagation, and its polarization. Interference is the superposition of two or more waves resulting in a new wave pattern. If the fields have components in the same direction, they constructively interfere, while opposite directions cause destructive interference. Additionally, multiple polarization signals can be combined (i.e. interfered) to form new states of polarization, which

1140-432: A deep-bluish-purple Wood's glass 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

1254-669: A filter coating which absorbs most visible light. Halogen lamps with fused quartz envelopes are used as inexpensive UV light sources in the near UV range, from 400 to 300 nm, in some scientific instruments. Due to its black-body spectrum a filament light bulb is a very inefficient ultraviolet source, emitting only a fraction of a percent of its energy as UV. Specialized UV gas-discharge lamps containing different gases produce UV radiation at particular spectral lines for scientific purposes. Argon and deuterium arc lamps are often used as stable sources, either windowless or with various windows such as magnesium fluoride . These are often

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1368-499: A fluorescence on a nearby plate of coated glass. In one month, he discovered X-rays' main properties. The last portion of the EM spectrum to be discovered was associated with radioactivity . Henri Becquerel found that uranium salts caused fogging of an unexposed photographic plate through a covering paper in a manner similar to X-rays, and Marie Curie discovered that only certain elements gave off these rays of energy, soon discovering

1482-471: A fourth color receptor for ultraviolet rays; this, coupled with eye structures that transmit more UV gives smaller birds "true" UV vision. "Ultraviolet" means "beyond violet" (from Latin ultra , "beyond"), violet being the color of the highest frequencies of visible light . Ultraviolet has a higher frequency (thus a shorter wavelength) than violet light. UV radiation was discovered in February 1801 when

1596-597: A given time and location. This standard shows that most sunburn happens due to UV at wavelengths near the boundary of the UVA and UVB bands. Overexposure to UVB radiation not only can cause sunburn but also some forms of skin cancer . However, the degree of redness and eye irritation (which are largely not caused by UVA) do not predict the long-term effects of UV, although they do mirror the direct damage of DNA by ultraviolet. Electromagnetic radiation In physics , electromagnetic radiation ( EMR ) consists of waves of

1710-576: A higher energy (and hence shorter wavelength) than gamma rays and vice versa. The origin of the ray differentiates them, gamma rays tend to be natural phenomena originating from the unstable nucleus of an atom and X-rays are electrically generated (and hence man-made) unless they are as a result of bremsstrahlung X-radiation caused by the interaction of fast moving particles (such as beta particles) colliding with certain materials, usually of higher atomic numbers. EM radiation (the designation 'radiation' excludes static electric and magnetic and near fields )

1824-528: A linear medium such as a vacuum. However, in nonlinear media, such as some crystals , interactions can occur between light and static electric and magnetic fields—these interactions include the Faraday effect and the Kerr effect . In refraction , a wave crossing from one medium to another of different density alters its speed and direction upon entering the new medium. The ratio of the refractive indices of

1938-539: A lower energy level, it emits a photon of light at a frequency corresponding to the energy difference. Since the energy levels of electrons in atoms are discrete, each element and each molecule emits and absorbs its own characteristic frequencies. Immediate photon emission is called fluorescence , a type of photoluminescence . An example is visible light emitted from fluorescent paints, in response to ultraviolet ( blacklight ). Many other fluorescent emissions are known in spectral bands other than visible light. Delayed emission

2052-550: A number of ranges recommended by the ISO standard 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 photocathodes , which can be tailored to be sensitive to different parts of

2166-417: A particular star. Spectroscopy is also used in the determination of the distance of a star, using the red shift . When any wire (or other conducting object such as an antenna ) conducts alternating current , electromagnetic radiation is propagated at the same frequency as the current. As a wave, light is characterized by a velocity (the speed of light ), wavelength , and frequency . As particles, light

2280-417: A receiver very close to the source, such as inside a transformer . The near field has strong effects its source, with any energy withdrawn by a receiver causing increased load (decreased electrical reactance ) on the source. The near field does not propagate freely into space, carrying energy away without a distance limit, but rather oscillates, returning its energy to the transmitter if it is not absorbed by

2394-467: A receiver. By contrast, the far field is composed of radiation that is free of the transmitter, in the sense that the transmitter requires the same power to send changes in the field out regardless of whether anything absorbs the signal, e.g. a radio station does not need to increase its power when more receivers use the signal. This far part of the electromagnetic field is electromagnetic radiation. The far fields propagate (radiate) without allowing

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2508-445: A third type of radiation, which in 1903 Rutherford named gamma rays . In 1910 British physicist William Henry Bragg demonstrated that gamma rays are electromagnetic radiation, not particles, and in 1914 Rutherford and Edward Andrade measured their wavelengths, finding that they were similar to X-rays but with shorter wavelengths and higher frequency, although a 'cross-over' between X and gamma rays makes it possible to have X-rays with

2622-519: 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. 'Black light' incandescent lamps are also made from an incandescent light bulb with

2736-448: A variety of wavelength bands into the vacuum ultraviolet. Light-emitting diodes (LEDs) can be manufactured to emit radiation in the ultraviolet range. In 2019, following significant advances over the preceding five years, UVA 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

2850-431: A very large (ideally infinite) distance from the source. Both types of waves can have a waveform which is an arbitrary time function (so long as it is sufficiently differentiable to conform to the wave equation). As with any time function, this can be decomposed by means of Fourier analysis into its frequency spectrum , or individual sinusoidal components, each of which contains a single frequency, amplitude and phase. Such

2964-467: A wave is its rate of oscillation and is measured in hertz , the SI unit of frequency, where one hertz is equal to one oscillation per second. Light usually has multiple frequencies that sum to form the resultant wave. Different frequencies undergo different angles of refraction, a phenomenon known as dispersion . A monochromatic wave (a wave of a single frequency) consists of successive troughs and crests, and

3078-473: Is ionizing radiation . Consequently, short-wave UV damages DNA and sterilizes surfaces with which it comes into contact. For humans, suntan and sunburn are familiar effects of exposure of the skin to UV, along with an increased risk of skin cancer . The amount of UV radiation 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

3192-522: Is quantized and proportional to frequency according to Planck's equation E = hf , where E is the energy per photon, f is the frequency of the photon, and h is the Planck constant . Thus, higher frequency photons have more energy. For example, a 10  Hz gamma ray photon has 10 times the energy of a 10  Hz extremely low frequency radio wave photon. The effects of EMR upon chemical compounds and biological organisms depend both upon

3306-472: Is a more subtle affair. Some experiments display both the wave and particle natures of electromagnetic waves, such as the self-interference of a single photon . When a single photon is sent through an interferometer , it passes through both paths, interfering with itself, as waves do, yet is detected by a photomultiplier or other sensitive detector only once. A quantum theory of the interaction between electromagnetic radiation and matter such as electrons

3420-404: Is a stream of photons . Each has an energy related to the frequency of the wave given by Planck's relation E = hf , where E is the energy of the photon, h is the Planck constant , 6.626 × 10 J·s, and f is the frequency of the wave. In a medium (other than vacuum), velocity factor or refractive index are considered, depending on frequency and application. Both of these are ratios of

3534-1046: 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 - 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 lasers . Ultraviolet lasers can also be made by applying frequency conversion to lower-frequency lasers. Ultraviolet lasers have applications in industry ( laser engraving ), medicine ( dermatology , and keratectomy ), chemistry ( MALDI ), free-air secure communications , computing ( optical storage ), and manufacture of integrated circuits. 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

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3648-523: Is associated with those EM waves that are free to propagate themselves ("radiate") without the continuing influence of the moving charges that produced them, because they have achieved sufficient distance from those charges. Thus, EMR is sometimes referred to as the far field , while the near field refers to EM fields near the charges and current that directly produced them, specifically electromagnetic induction and electrostatic induction phenomena. In quantum mechanics , an alternate way of viewing EMR

3762-422: Is called phosphorescence . The modern theory that explains the nature of light includes the notion of wave–particle duality. Together, wave and particle effects fully explain the emission and absorption spectra of EM radiation. The matter-composition of the medium through which the light travels determines the nature of the absorption and emission spectrum. These bands correspond to the allowed energy levels in

3876-563: Is classified by wavelength into radio , microwave , infrared , visible , ultraviolet , X-rays and gamma rays . Arbitrary electromagnetic waves can be expressed by Fourier analysis in terms of sinusoidal waves ( monochromatic radiation ), which in turn can each be classified into these regions of the EMR spectrum. For certain classes of EM waves, the waveform is most usefully treated as random , and then spectral analysis must be done by slightly different mathematical techniques appropriate to random or stochastic processes . In such cases,

3990-408: Is composed of about 50% infrared light, 40% visible light, and 10% ultraviolet light, for a total intensity of about 1400 W/m 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

4104-647: Is consequently absorbed by a wide range of substances, causing them to increase in temperature as the vibrations dissipate as heat. The same process, run in reverse, causes bulk substances to radiate in the infrared spontaneously (see thermal radiation section below). Infrared radiation is divided into spectral subregions. While different subdivision schemes exist, the spectrum is commonly divided as near-infrared (0.75–1.4 μm), short-wavelength infrared (1.4–3 μm), mid-wavelength infrared (3–8 μm), long-wavelength infrared (8–15 μm) and far infrared (15–1000 μm). Annalen der Physik The journal

4218-470: Is conventionally taken as 400 nm, so ultraviolet rays are not visible 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. Ultraviolet rays are usually 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

4332-729: Is described by the theory of quantum electrodynamics . Electromagnetic waves can be polarized , reflected, refracted, or diffracted , and can interfere with each other. In homogeneous, isotropic media, electromagnetic radiation is a transverse wave , meaning that its oscillations are perpendicular to the direction of energy transfer and travel. It comes from the following equations : ∇ ⋅ E = 0 ∇ ⋅ B = 0 {\displaystyle {\begin{aligned}\nabla \cdot \mathbf {E} &=0\\\nabla \cdot \mathbf {B} &=0\end{aligned}}} These equations predicate that any electromagnetic wave must be

4446-447: 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

4560-493: 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. UV rays also treat certain skin conditions. Modern phototherapy has been used to successfully treat psoriasis , eczema , jaundice , vitiligo , atopic dermatitis , and localized scleroderma . In addition, UV radiation, in particular UVB radiation, has been shown to induce cell cycle arrest in keratinocytes ,

4674-453: Is known as parallel polarization state generation . The energy in electromagnetic waves is sometimes called radiant energy . An anomaly arose in the late 19th century involving a contradiction between the wave theory of light and measurements of the electromagnetic spectra that were being emitted by thermal radiators known as black bodies . Physicists struggled with this problem unsuccessfully for many years, and it later became known as

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4788-417: 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

4902-511: 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 sources can also produce all wavelengths of UV, including those at the boundary of the UV and X‑ray spectra at 10 nm. The impact of ultraviolet radiation on human health has implications for

5016-494: Is planned to be used to calibrate the color cameras for the 2019 ESA Mars rover mission, since they will remain unfaded by the high level of UV present at the surface of Mars. Common soda–lime glass , such as window glass, is partially transparent to UVA, but is opaque 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

5130-477: Is that it consists of photons , uncharged elementary particles with zero rest mass which are the quanta of the electromagnetic field , responsible for all electromagnetic interactions. Quantum electrodynamics is the theory of how EMR interacts with matter on an atomic level. Quantum effects provide additional sources of EMR, such as the transition of electrons to lower energy levels in an atom and black-body radiation . The energy of an individual photon

5244-486: Is the emission spectrum of nebulae . Rapidly moving electrons are most sharply accelerated when they encounter a region of force, so they are responsible for producing much of the highest frequency electromagnetic radiation observed in nature. These phenomena can aid various chemical determinations for the composition of gases lit from behind (absorption spectra) and for glowing gases (emission spectra). Spectroscopy (for example) determines what chemical elements comprise

5358-426: Is the successor to Journal der Physik , published from 1790 until 1794, and Neues Journal der Physik , published from 1795 until 1797. The journal has been published under a variety of names ( Annalen der Physik , Annalen der Physik und der physikalischen Chemie , Annalen der Physik und Chemie , Wiedemann's Annalen der Physik und Chemie ) during its history. Originally, Annalen der Physik

5472-648: The Planck energy or exceeding it (far too high to have ever been observed) will require new physical theories to describe. When radio waves impinge upon a conductor , they couple to the conductor, travel along it and induce an electric current on the conductor surface by moving the electrons of the conducting material in correlated bunches of charge. Electromagnetic radiation phenomena with wavelengths ranging from as long as one meter to as short as one millimeter are called microwaves; with frequencies between 300 MHz (0.3 GHz) and 300 GHz. At radio and microwave frequencies, EMR interacts with matter largely as

5586-473: The Planck–Einstein equation . In quantum theory (see first quantization ) the energy of the photons is thus directly proportional to the frequency of the EMR wave. Likewise, the momentum p of a photon is also proportional to its frequency and inversely proportional to its wavelength: The source of Einstein's proposal that light was composed of particles (or could act as particles in some circumstances)

5700-537: The UV degradation (photo-oxidation) of a material. The absorbers can themselves degrade over time, so monitoring of absorber levels in weathered materials is necessary. In sunscreen , ingredients that absorb UVA/UVB rays, such as avobenzone , oxybenzone and octyl methoxycinnamate , are organic chemical absorbers or "blockers". They are contrasted with inorganic absorbers/"blockers" of UV radiation such as carbon black , titanium dioxide , and zinc oxide . For clothing,

5814-418: 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, UV (specifically, UVB) is also responsible for the formation of vitamin D in most land vertebrates , including humans. The UV spectrum, thus, has effects both beneficial and detrimental to life. The lower wavelength limit of the visible spectrum

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5928-462: The cornea . Humans also lack color receptor adaptations for ultraviolet rays. Nevertheless, the photoreceptors of the retina are sensitive to near-UV, and people lacking a lens (a condition known as aphakia ) perceive near-UV as whitish-blue or whitish-violet. 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

6042-523: The electromagnetic (EM) field , which propagate through space and carry momentum and electromagnetic radiant energy . Classically , electromagnetic radiation consists of electromagnetic waves , which are synchronized oscillations of electric and magnetic fields . In a vacuum , electromagnetic waves travel at the speed of light , commonly denoted c . There, depending on the frequency of oscillation, different wavelengths of electromagnetic spectrum are produced. In homogeneous, isotropic media,

6156-418: The ultraviolet catastrophe . In 1900, Max Planck developed a new theory of black-body radiation that explained the observed spectrum. Planck's theory was based on the idea that black bodies emit light (and other electromagnetic radiation) only as discrete bundles or packets of energy. These packets were called quanta . In 1905, Albert Einstein proposed that light quanta be regarded as real particles. Later

6270-459: The ultraviolet protection factor (UPF) represents the ratio of sunburn -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

6384-644: The EUV spectrum is set by a prominent He spectral line at 30.4 nm. EUV is strongly absorbed by most known materials, but synthesizing multilayer optics that reflect up to about 50% of EUV radiation at normal incidence is possible. This technology was pioneered by the NIXT and MSSTA sounding rockets in the 1990s, and it has been used to make telescopes for solar imaging. See also the Extreme Ultraviolet Explorer satellite . Some sources use

6498-562: The German physicist Johann Wilhelm Ritter observed that invisible rays just beyond the violet end of the visible spectrum darkened silver chloride -soaked paper more quickly than violet light itself. He announced the discovery in a very brief letter to the Annalen der Physik and later called them "(de-)oxidizing rays" ( German : de-oxidierende Strahlen ) to emphasize chemical reactivity and to distinguish them from " heat rays ", discovered

6612-485: The German physics community", alongside Physikalische Zeitschrift . Between 1944 and 1946 publication ceased due to World War II . Granted permission to restart by Soviet military authorities in August 1946, the journal subsequently maintained a policy until 1992 of co-editorship by one person from East Germany and one from West Germany. After German reunification, the journal was acquired by Wiley-VCH . A relaunch of

6726-430: 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. Ultraviolet absorbers are molecules used in organic materials ( polymers , paints , etc.) to absorb UV radiation to reduce

6840-556: The UV spectrum. Sensitive UV photomultipliers are available. Spectrometers 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 in the air, though the longer wavelengths around 150–200 nm can propagate through nitrogen . Scientific instruments can, therefore, use this spectral range by operating in an oxygen-free atmosphere (pure nitrogen, or argon for shorter wavelengths), without

6954-671: 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 , depending on quality, can be transparent even to vacuum UV wavelengths. Crystalline quartz and some crystals such as CaF 2 and MgF 2 transmit well down to 150 nm or 160 nm wavelengths. Wood's glass is a deep violet-blue barium-sodium silicate glass with about 9% nickel(II) oxide developed during World War I to block visible light for covert communications. It allows both infrared daylight and ultraviolet night-time communications by being transparent between 320 nm and 400 nm and also

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7068-827: The UVA 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 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 (30 kW/m) are now possible, and this, coupled with recent developments by photo-initiator and resin formulators, makes

7182-483: The UVC band at 253.7 nm and 185 nm due to the mercury within the lamp, as well as some visible light. From 85% to 90% of the UV produced by these lamps is at 253.7 nm, whereas only 5–10% is at 185 nm. The fused quartz tube passes the 253.7 nm radiation but blocks the 185 nm wavelength. Such tubes have two or three times the UVC power of a regular fluorescent lamp tube. These low-pressure lamps have

7296-432: The atoms in the star's atmosphere. A similar phenomenon occurs for emission , which is seen when an emitting gas glows due to excitation of the atoms from any mechanism, including heat. As electrons descend to lower energy levels, a spectrum is emitted that represents the jumps between the energy levels of the electrons, but lines are seen because again emission happens only at particular energies after excitation. An example

7410-413: The atoms. Dark bands in the absorption spectrum are due to the atoms in an intervening medium between source and observer. The atoms absorb certain frequencies of the light between emitter and detector/eye, then emit them in all directions. A dark band appears to the detector, due to the radiation scattered out of the light beam . For instance, dark bands in the light emitted by a distant star are due to

7524-403: The average number of photons in the cube of the relevant wavelength is much smaller than 1. It is not so difficult to experimentally observe non-uniform deposition of energy when light is absorbed, however this alone is not evidence of "particulate" behavior. Rather, it reflects the quantum nature of matter . Demonstrating that the light itself is quantized, not merely its interaction with matter,

7638-584: The beginning of the UVB band at 315 nm, and rapidly increasing to 300 nm. The skin and eyes are most sensitive to damage by UV at 265–275 nm, which is in the lower UVC band. At still shorter wavelengths of UV, damage continues to happen, but the overt effects are not as great with so little penetrating the atmosphere. The WHO -standard ultraviolet index is a widely publicized measurement of total strength of UV wavelengths that cause sunburn on human skin, by weighting UV exposure for action spectrum effects at

7752-402: The colored glow that many substances give off when exposed to UV light. UVA / UVB emitting bulbs are also sold for other special purposes, such as tanning lamps and reptile-husbandry. Shortwave UV lamps are made using a fluorescent lamp tube with no phosphor coating, composed of fused quartz or vycor , since ordinary glass absorbs UVC. These lamps emit ultraviolet light with two peaks in

7866-408: The combined energy transfer of many photons. In contrast, high frequency ultraviolet, X-rays and gamma rays are ionizing – individual photons of such high frequency have enough energy to ionize molecules or break chemical bonds . Ionizing radiation can cause chemical reactions and damage living cells beyond simply heating, and can be a health hazard and dangerous. James Clerk Maxwell derived

7980-525: The development of solar-blind devices has been an important area of research. Wide-gap solid-state devices or vacuum devices with high-cutoff photocathodes can be attractive compared to silicon diodes. Extreme UV (EUV or sometimes XUV) is characterized by a transition in the physics of interaction with matter. Wavelengths longer than about 30 nm interact mainly with the outer valence electrons of atoms, while wavelengths shorter than that interact mainly with inner-shell electrons and nuclei. The long end of

8094-400: The distance between two adjacent crests or troughs is called the wavelength . Waves of the electromagnetic spectrum vary in size, from very long radio waves longer than a continent to very short gamma rays smaller than atom nuclei. Frequency is inversely proportional to wavelength, according to the equation: where v is the speed of the wave ( c in a vacuum or less in other media), f is

8208-580: The distinction of "hard UV" and "soft UV". For instance, in the case of astrophysics , the boundary may be at the Lyman limit (wavelength 91.2 nm, the energy needed to ionise a hydrogen atom from its ground state), with "hard UV" being more energetic; the same terms may also be used in other fields, such as cosmetology , optoelectronic , 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

8322-500: The editor's name: Gilberts Annalen , Poggendorfs Annalen , Wiedemanns Annalen and so on, or for short Pogg. Ann. , Wied. Ann. After Drude, the work was divided between two editors: experimentalists Wilhelm Wien (1907–1928) and Eduard Grüneisen (1929–1949) and theoretician Max Planck (1907–1943, who had been associate editor from 1895). In these times, peer-review was not yet standard. Einstein, for example, just sent his manuscripts to Planck, who then published them. Some of

8436-524: The electromagnetic spectrum includes: radio waves , microwaves , infrared , visible light , ultraviolet , X-rays , and gamma rays . Electromagnetic waves are emitted by electrically charged particles undergoing acceleration , and these waves can subsequently interact with other charged particles, exerting force on them. EM waves carry energy, momentum , and angular momentum away from their source particle and can impart those quantities to matter with which they interact. Electromagnetic radiation

8550-447: The electromagnetic vacuum. The behavior of EM radiation and its interaction with matter depends on its frequency, and changes qualitatively as the frequency changes. Lower frequencies have longer wavelengths, and higher frequencies have shorter wavelengths, and are associated with photons of higher energy. There is no fundamental limit known to these wavelengths or energies, at either end of the spectrum, although photons with energies near

8664-461: The emitting sources in UV spectroscopy equipment for chemical analysis. Other UV sources with more continuous emission spectra include xenon arc lamps (commonly used as sunlight simulators), deuterium arc lamps , mercury-xenon arc lamps , and metal-halide arc lamps . The excimer lamp , a UV source developed in the early 2000s, is seeing increasing use in scientific fields. It has the advantages of high-intensity, high efficiency, and operation at

8778-574: 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

8892-478: The expansion of LED cured UV materials likely. UVC 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 lamps . Also, they are used as line sources to replace deuterium lamps in liquid chromatography instruments. Gas lasers , laser diodes , and solid-state lasers can be manufactured to emit ultraviolet rays, and lasers are available that cover

9006-580: 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 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 ,

9120-527: The fields present in the same space due to other causes. Further, as they are vector fields, all magnetic and electric field vectors add together according to vector addition . For example, in optics two or more coherent light waves may interact and by constructive or destructive interference yield a resultant irradiance deviating from the sum of the component irradiances of the individual light waves. The electromagnetic fields of light are not affected by traveling through static electric or magnetic fields in

9234-406: The frequency and λ is the wavelength. As waves cross boundaries between different media, their speeds change but their frequencies remain constant. Electromagnetic waves in free space must be solutions of Maxwell's electromagnetic wave equation . Two main classes of solutions are known, namely plane waves and spherical waves. The plane waves may be viewed as the limiting case of spherical waves at

9348-541: The ground right into early summer and sun positions even at zenith are low, are particularly at risk. Skin, the circadian system, and the immune system 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 and skin redness (with lighter skinned individuals being more sensitive) at wavelengths starting near

9462-477: The individual frequency components are represented in terms of their power content, and the phase information is not preserved. Such a representation is called the power spectral density of the random process. Random electromagnetic radiation requiring this kind of analysis is, for example, encountered in the interior of stars, and in certain other very wideband forms of radiation such as the Zero point wave field of

9576-544: The intense radiation of radium . The radiation from pitchblende was differentiated into alpha rays ( alpha particles ) and beta rays ( beta particles ) by Ernest Rutherford through simple experimentation in 1899, but these proved to be charged particulate types of radiation. However, in 1900 the French scientist Paul Villard discovered a third neutrally charged and especially penetrating type of radiation from radium, and after he described it, Rutherford realized it must be yet

9690-406: The journal with new editor and new contents was announced for 2012. As a result of the 2012 relaunch, Annalen der Physik changed scope and updated the membership of the editorial board . The early editors-in-chief were: With each editor, the numbering of volumes restarted from 1 (co-existent with a continuous numbering, a perpetual source of confusion). The journal was often referred to by

9804-403: The journal. The importance of Annalen der Physik unquestionably peaked in 1905 with Albert Einstein 's Annus Mirabilis papers . In the 1920s, the journal lost ground to the concurrent Zeitschrift für Physik . With the 1933 emigration wave, German-language journals lost many of their best authors. During Nazi Germany , it was considered to represent "the more conservative elements within

9918-800: The known speed of light. Maxwell therefore suggested that visible light (as well as invisible infrared and ultraviolet rays by inference) all consisted of propagating disturbances (or radiation) in the electromagnetic field. Radio waves were first produced deliberately by Heinrich Hertz in 1887, using electrical circuits calculated to produce oscillations at a much lower frequency than that of visible light, following recipes for producing oscillating charges and currents suggested by Maxwell's equations. Hertz also developed ways to detect these waves, and produced and characterized what were later termed radio waves and microwaves . Wilhelm Röntgen discovered and named X-rays . After experimenting with high voltages applied to an evacuated tube on 8 November 1895, he noticed

10032-407: The lack of suitable gas / vapor cell window materials above the lithium fluoride cut-off wavelength limit the tuning range to longer than about 110 nm. Tunable V‑UV wavelengths down to 75 nm was achieved using window-free configurations. 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

10146-418: The longer infrared and just-barely-visible red wavelengths. Its maximum UV transmission is at 365 nm, one of the wavelengths of mercury lamps . A black light lamp emits long-wave UVA radiation and little visible light. Fluorescent black light lamps work similarly to other fluorescent lamps , but use a phosphor on the inner tube surface which emits UVA radiation instead of visible light. Some lamps use

10260-447: The media determines the degree of refraction, and is summarized by Snell's law . Light of composite wavelengths (natural sunlight) disperses into a visible spectrum passing through a prism, because of the wavelength-dependent refractive index of the prism material ( dispersion ); that is, each component wave within the composite light is bent a different amount. EM radiation exhibits both wave properties and particle properties at

10374-567: The minimum energy required to ionize atoms . Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack sufficient energy, it can induce chemical reactions and cause many substances to glow or fluoresce . Many practical applications, including chemical and biological effects, are derived from the way that UV radiation can interact with organic molecules. These interactions can involve absorption or adjusting energy states in molecules, but do not necessarily involve heating. Short-wave ultraviolet light

10488-471: 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. In humans, excessive exposure to UV radiation can result in acute and chronic harmful effects on the eye's dioptric system and retina . The risk is elevated at high altitudes and people living in high latitude areas where snow covers

10602-407: The nearby violet light. Ritter's experiments were an early precursor to what would become photography. Ritter noted that the ultraviolet rays (which at first were called "chemical rays") were capable of causing chemical reactions. In 1862–64 James Clerk Maxwell developed equations for the electromagnetic field which suggested that waves in the field would travel with a speed that was very close to

10716-485: The need for costly vacuum chambers. Significant examples include 193-nm photolithography equipment (for semiconductor manufacturing ) and circular dichroism spectrometers. Technology for VUV instrumentation was largely driven by solar astronomy for many decades. While optics can be used to remove unwanted visible light that contaminates the VUV, in general, detectors can be limited by their response to non-VUV radiation, and

10830-626: The oscillations of the two fields are on average perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave . Electromagnetic radiation is commonly referred to as "light", EM, EMR, or electromagnetic waves. The position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength. Electromagnetic waves of different frequency are called by different names since they have different sources and effects on matter. In order of increasing frequency and decreasing wavelength,

10944-401: The particle of light was given the name photon , to correspond with other particles being described around this time, such as the electron and proton . A photon has an energy, E , proportional to its frequency, f , by where h is the Planck constant , λ {\displaystyle \lambda } is the wavelength and c is the speed of light . This is sometimes known as

11058-450: 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 radiation , respectively. In 1878,

11172-428: The radiation's power and its frequency. EMR of lower energy ultraviolet or lower frequencies (i.e., near ultraviolet , visible light, infrared, microwaves, and radio waves) is non-ionizing because its photons do not individually have enough energy to ionize atoms or molecules or to break chemical bonds . The effect of non-ionizing radiation on chemical systems and living tissue is primarily simply heating, through

11286-470: The red part of the spectrum, through an increase in the temperature recorded with a thermometer . These "calorific rays" were later termed infrared. In 1801, German physicist Johann Wilhelm Ritter discovered ultraviolet in an experiment similar to Herschel's, using sunlight and a glass prism. Ritter noted that invisible rays near the violet edge of a solar spectrum dispersed by a triangular prism darkened silver chloride preparations more quickly than did

11400-512: The risks and benefits of sun exposure and is also implicated in issues such as fluorescent lamps and health . Getting too much sun exposure can be harmful, but in moderation, sun exposure is beneficial. UV (specifically, UVB) causes the body to produce vitamin D , which is essential for life. Humans need some UV radiation to maintain adequate vitamin D levels. According to the World Health Organization: There

11514-412: The same points in space (see illustrations). In the far-field EM radiation which is described by the two source-free Maxwell curl operator equations, a time-change in one type of field is proportional to the curl of the other. These derivatives require that the E and B fields in EMR are in-phase (see mathematics section below). An important aspect of light's nature is its frequency . The frequency of

11628-464: The same time (see wave-particle duality ). Both wave and particle characteristics have been confirmed in many experiments. Wave characteristics are more apparent when EM radiation is measured over relatively large timescales and over large distances while particle characteristics are more evident when measuring small timescales and distances. For example, when electromagnetic radiation is absorbed by matter, particle-like properties will be more obvious when

11742-460: 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 UVA and UVB. The shorter bands of UVC, as well as even more-energetic UV radiation produced by

11856-472: The source, the power density of EM radiation from an isotropic source decreases with the inverse square of the distance from the source; this is called the inverse-square law . This is in contrast to dipole parts of the EM field, the near field, which varies in intensity according to an inverse cube power law, and thus does not transport a conserved amount of energy over distances but instead fades with distance, with its energy (as noted) rapidly returning to

11970-549: The speed in a medium to speed in a vacuum. Electromagnetic radiation of wavelengths other than those of visible light were discovered in the early 19th century. The discovery of infrared radiation is ascribed to astronomer William Herschel , who published his results in 1800 before the Royal Society of London . Herschel used a glass prism to refract light from the Sun and detected invisible rays that caused heating beyond

12084-584: The sterilizing effect of short-wavelength light by killing bacteria was discovered. By 1903, the most effective wavelengths were known to be around 250 nm. In 1960, the effect of ultraviolet radiation on DNA was established. The discovery of the ultraviolet radiation with wavelengths below 200 nm, named "vacuum ultraviolet" because it is strongly absorbed by the oxygen in air, was made in 1893 by German physicist Victor Schumann . The electromagnetic spectrum of ultraviolet radiation (UVR), defined most broadly as 10–400 nanometers, can be subdivided into

12198-410: The term associated with the changing static electric field of the particle and the magnetic term that results from the particle's uniform velocity are both associated with the near field, and do not comprise electromagnetic radiation. Electric and magnetic fields obey the properties of superposition . Thus, a field due to any particular particle or time-varying electric or magnetic field contributes to

12312-475: The transmitter or absorbed by a nearby receiver (such as a transformer secondary coil). In the Liénard–Wiechert potential formulation of the electric and magnetic fields due to motion of a single particle (according to Maxwell's equations), the terms associated with acceleration of the particle are those that are responsible for the part of the field that is regarded as electromagnetic radiation. By contrast,

12426-427: The transmitter to affect them. This causes them to be independent in the sense that their existence and their energy, after they have left the transmitter, is completely independent of both transmitter and receiver. Due to conservation of energy , the amount of power passing through any spherical surface drawn around the source is the same. Because such a surface has an area proportional to the square of its distance from

12540-476: The tunable range of the 4 wave mixing. Difference frequency mixing (i.e., f 1 + f 2 − f 3 ) has an advantage over sum frequency mixing because the phase matching can provide greater tuning. In particular, difference frequency mixing two photons of an Ar F (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,

12654-499: 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 UVA and 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 in

12768-524: The wave theory, however, Einstein's ideas were met initially with great skepticism among established physicists. Eventually Einstein's explanation was accepted as new particle-like behavior of light was observed, such as the Compton effect . As a photon is absorbed by an atom , it excites the atom, elevating an electron to a higher energy level (one that is on average farther from the nucleus). When an electron in an excited molecule or atom descends to

12882-422: Was an experimental anomaly not explained by the wave theory: the photoelectric effect , in which light striking a metal surface ejected electrons from the surface, causing an electric current to flow across an applied voltage . Experimental measurements demonstrated that the energy of individual ejected electrons was proportional to the frequency , rather than the intensity , of the light. Furthermore, below

12996-509: Was published in German , then a leading scientific language. From the 1950s to the 1980s, the journal published in both German and English. Initially, only foreign authors contributed articles in English but from the 1970s German-speaking authors increasingly wrote in English in order to reach an international audience. After the German reunification in 1990, English became the only language of

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