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Infrared (IR), sometimes called infrared light, is
electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. ...

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

wavelength
s longer than those of
visible light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nano ...

visible light
. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around 1 
millimeter The millimetre ( international spelling; SI unit symbol mm) or millimeter ( American spelling) is a unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' ...
(300 
GHz The hertz (symbol: Hz) is the unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of action (or beat) in a theatric ...
) to the nominal
red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength Image:dominant wavelength.png, frame, Dominant/complementary wavelength example on the CIE color ...

red
edge of the
visible spectrum The visible spectrum is the portion of the that is to the . in this range of s is called ' or simply . A typical will respond to wavelengths from about 380 to about 750 . In terms of frequency, this corresponds to a band in the vicinity of ...
, around 700 
nanometer file:EM Spectrum Properties edit.svg, 330px, Different lengths as in respect to the Electromagnetic spectrum, measured by the Metre and its derived scales. The nanometre is often used to express dimensions on an atomic scale and mostly in the Mo ...
s (430  THz) (although the longer IR wavelengths are often designated rather as
terahertz radiation Terahertz radiation – also known as submillimeter radiation, terahertz waves, tremendously high frequency (THF), T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic wave Electromagnetism is a branch of physic ...
).
Black-body radiation Black-body radiation is the within or surrounding a body in with its environment, emitted by a (an idealized opaque, non-reflective body). It has a specific spectrum of wavelengths, inversely related to intensity that depend only on the bod ...
from objects near room temperature is almost all at infrared wavelengths. As a form of electromagnetic radiation, IR propagates
energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regula ...

energy
and
momentum In Newtonian mechanics, linear momentum, translational momentum, or simply momentum is the product of the mass Mass is both a property Property (''latin: Res Privata'') in the Abstract and concrete, abstract is what belongs to or w ...

momentum
, with properties corresponding to both those of a
wave In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular su ...

wave
and of a
particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object to which can be ascribed several physical property, physical or chemical property, chemical p ...
, the
photon The photon ( el, φῶς, phōs, light) is a type of elementary particle In , an elementary particle or fundamental particle is a that is not composed of other particles. Particles currently thought to be elementary include the fundamental s ...

photon
. Infrared radiation was discovered in 1800 by astronomer Sir
William Herschel Sir Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a spe ...

William Herschel
, who discovered a type of invisible radiation in the spectrum lower in energy than red light, by means of its effect on a
thermometer (mercury-in-glass thermometer) for measurement of room temperature. A thermometer is a device that temperature measurement, measures temperature or a temperature gradient A temperature gradient is a physical quantity that describes in which dir ...

thermometer
. Slightly more than half of the energy from the
Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

Sun
was eventually found, through Herschel's studies, to arrive on
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
in the form of infrared. The balance between absorbed and emitted infrared radiation has an important effect on Earth's
climate Climate is the long-term pattern of weather Weather is the state of the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a la ...

climate
. Infrared radiation is emitted or absorbed by
molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon ...

molecule
s when changing
rotational-vibrational
rotational-vibrational
movements. It excites
vibration Vibration is a mechanical phenomenon whereby oscillation Oscillation is the repetitive variation, typically in time Time is the indefinite continued sequence, progress of existence and event (philosophy), events that occur in an apparentl ...

vibration
al modes in a
molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon ...

molecule
through a change in the
dipole momentDipole moment may refer to: *Electric dipole moment, the measure of the electrical polarity of a system of charges **Transition dipole moment, the electrical dipole moment in quantum mechanics **Molecular dipole moment, the electric dipole moment o ...
, making it a useful frequency range for study of these energy states for molecules of the proper symmetry.
Infrared spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption spectroscopy, absorption, emission spectrum, emission, or reflection (physics), reflection. ...

Infrared spectroscopy
examines absorption and transmission of
photon The photon ( el, φῶς, phōs, light) is a type of elementary particle In , an elementary particle or fundamental particle is a that is not composed of other particles. Particles currently thought to be elementary include the fundamental s ...

photon
s in the infrared range. Infrared radiation is used in industrial, scientific, military, commercial, and medical applications. Night-vision devices using active near-infrared illumination allow people or animals to be observed without the observer being detected.
Infrared astronomy Infrared astronomy is a sub-discipline of astronomy which specializes in the astronomical observation, observation and analysis of astronomical objects using infrared (IR) radiation. The wavelength of infrared light ranges from 0.75 to 300 micro ...
uses sensor-equipped
telescope A telescope is an optical instrument An optical instrument (or "optic" for short) is a device that processes light waves (or photons), either to enhance an image for viewing or to analyze and determine their characteristic properties. Common ...

telescope
s to penetrate dusty regions of space such as
molecular cloud A molecular cloud, sometimes called a stellar nursery (if star formation is occurring within), is a type of interstellar cloud, the density and size of which permit absorption nebulae, the formation of molecules (most commonly molecular hydrogen, ...
s, to detect objects such as
planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and ...

planet
s, and to view highly
red-shifted
red-shifted
objects from the early days of the
universe The universe ( la, universus) is all of space and time and their contents, including planets, stars, galaxy, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development ...

universe
. Infrared thermal-imaging cameras are used to detect heat loss in insulated systems, to observe changing blood flow in the skin, and to detect the overheating of electrical components. Military and civilian applications include
target acquisition Target acquisition is the detection and identification of the location of a target in sufficient detail to permit the effective employment of lethal and non-lethal means. The term is used for a broad area of applications. A "target" here is an ent ...
,
surveillance Surveillance is the monitoring of behavior, many activities, or information for the purpose of information gathering, influencing, managing Management (or managing) is the administration of an organization An organization, or org ...

surveillance
,
night vision Night vision is the ability to see in low-light conditions, either naturally with scotopic vision Scotopic vision is the vision of the eye under low-light Light or visible light is electromagnetic radiation within the portion of the elec ...

night vision
, homing, and tracking. Humans at normal body temperature radiate chiefly at wavelengths around 10 μm (micrometers). Non-military uses include
thermal efficiency In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quan ...
analysis, environmental monitoring, industrial facility inspections, detection of
grow-ops This article presents common techniques and facts regarding the cultivation of cannabis, primarily for the production and consumption of its infructescences ("buds" or "flowers"). Cultivation techniques for other purposes (such as hemp He ...
, remote temperature sensing, short-range
wireless communication Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points that do not use an electrical conductor In physics Physics is the natural science that studies matter, its ...
,
spectroscopy Spectroscopy is the study of the interaction Interaction is a kind of action that occurs as two or more objects have an effect upon one another. The idea of a two-way effect is essential in the concept of interaction, as opposed to a one-way ...

spectroscopy
, and
weather forecasting Weather forecasting is the application of science and technology to predict the conditions of the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' o ...
.


Definition and relationship to the electromagnetic spectrum

Infrared radiation extends from the nominal
red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength Image:dominant wavelength.png, frame, Dominant/complementary wavelength example on the CIE color ...

red
edge of the
visible spectrum The visible spectrum is the portion of the that is to the . in this range of s is called ' or simply . A typical will respond to wavelengths from about 380 to about 750 . In terms of frequency, this corresponds to a band in the vicinity of ...
at 700
nanometers one nanometric Scanning_Tunneling_Microscope.html"_;"title="carbon_nano_tube,_photographed_with_Scanning_Tunneling_Microscope">carbon_nano_tube,_photographed_with_Scanning_Tunneling_Microscope_ file:EM_Spectrum_Properties_edit.svg.html" ;"title= ...
(nm) to 1
millimeter The millimetre ( international spelling; SI unit symbol mm) or millimeter ( American spelling) is a unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' ...
(mm). This range of wavelengths corresponds to a
frequency Frequency is the number of occurrences of a repeating event per unit of time A unit of time is any particular time Time is the indefinite continued sequence, progress of existence and event (philosophy), events that occur in an apparen ...
range of approximately 430  THz down to 300 
GHz The hertz (symbol: Hz) is the unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of action (or beat) in a theatric ...
. Beyond infrared is the microwave portion of the
electromagnetic spectrum The electromagnetic spectrum is the range of frequency, frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energy, photon energies. The electromagnetic spectrum covers electromagnetic waves with f ...

electromagnetic spectrum
.


Natural infrared

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

Sunlight
, at an effective temperature of 5,780 
kelvin The kelvin is the base unit of temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal en ...

kelvin
s (5,510 °C, 9,940 °F), is composed of near-thermal-spectrum radiation that is slightly more than half infrared. At zenith, sunlight provides an
irradiance In radiometry Radiometry is a set of techniques for measuring ' Measurement is the numerical quantification of the attributes of an object or event, which can be used to compare with other objects or events. The scope and application of measure ...

irradiance
of just over 1 
kilowatt The watt (symbol: W) is a unit of power Power typically refers to: * Power (physics) In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equa ...

kilowatt
per square meter at sea level. Of this energy, 527 watts is infrared radiation, 445 watts is
visible light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nano ...
, and 32 watts is
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, ...

ultraviolet
radiation. Nearly all the infrared radiation in sunlight is near infrared, shorter than 4 micrometers. On the surface of Earth, at far lower temperatures than the surface of the Sun, some thermal radiation consists of infrared in the mid-infrared region, much longer than in sunlight. However, black-body, or thermal, radiation is continuous: it gives off radiation at all wavelengths. Of these natural thermal radiation processes, only lightning and natural fires are hot enough to produce much visible energy, and fires produce far more infrared than visible-light energy.


Regions within the infrared

In general, objects emit infrared radiation across a spectrum of wavelengths, but sometimes only a limited region of the spectrum is of interest because sensors usually collect radiation only within a specific bandwidth. Thermal infrared radiation also has a maximum emission wavelength, which is inversely proportional to the absolute temperature of object, in accordance with
Wien's displacement law upright=1.45, Black-body radiation as a function of wavelength for various temperatures. Each temperature curve peaks at a different wavelength and Wien's law describes the shift of that peak. Wien's displacement law states that the black-body r ...
. The infrared band is often subdivided into smaller sections, although how the IR spectrum is thereby divided varies between different areas in which IR is employed.


Visible limit

Infrared radiation is generally considered to begin with wavelengths longer than visible by the human eye. However there is no ''hard'' wavelength limit to what is visible, as the eye's sensitivity decreases rapidly but smoothly, for wavelengths exceeding about 700 nm. Therefore wavelengths just longer than that can be seen if they are sufficiently bright, though they may still be classified as infrared according to usual definitions. Light from a near-IR laser may thus appear dim red and can present a hazard since it may actually be quite bright. And even IR at wavelengths up to 1,050 nm from pulsed lasers can be seen by humans under certain conditions.


Commonly used sub-division scheme

A commonly used sub-division scheme is: NIR and SWIR together is sometimes called "reflected infrared", whereas MWIR and LWIR is sometimes referred to as "thermal infrared".


CIE division scheme

The
International Commission on Illumination The International Commission on Illumination (usually abbreviated CIE for its French name, Commission internationale de l'éclairage) is the international authority on light Light or visible light is electromagnetic radiation within the port ...
(CIE) recommended the division of infrared radiation into the following three bands:


ISO 20473 scheme

ISO The International Organization for Standardization (ISO ) is an international standard An international standard is a technical standard A technical standard is an established norm (social), norm or requirement for a repeatable technical task w ...
20473 specifies the following scheme:


Astronomy division scheme

Astronomers typically divide the infrared spectrum as follows: These divisions are not precise and can vary depending on the publication. The three regions are used for observation of different temperature ranges, and hence different environments in space. The most common photometric system used in astronomy allocates capital letters to different spectral regions according to filters used; I, J, H, and K cover the near-infrared wavelengths; L, M, N, and Q refer to the mid-infrared region. These letters are commonly understood in reference to atmospheric windows and appear, for instance, in the titles of many
papers Paper is a thin, flat material produced by the compression of fibres. Paper(s) or The Paper may also refer to: Publishing and academia * Newspaper, a periodical publication * Paper (magazine), ''Paper'' (magazine), an American monthly fashion and ...
.


Sensor response division scheme

A third scheme divides up the band based on the response of various detectors:Miller, ''Principles of Infrared Technology'' (Van Nostrand Reinhold, 1992), and Miller and Friedman, ''Photonic Rules of Thumb'', 2004. * Near-infrared: from 0.7 to 1.0 μm (from the approximate end of the response of the human eye to that of silicon). * Short-wave infrared: 1.0 to 3 μm (from the cut-off of silicon to that of the MWIR atmospheric window).
InGaAs Indium gallium arsenide (InGaAs) (alternatively gallium indium arsenide, GaInAs) is a ternary alloy (chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and genera ...
covers to about 1.8 μm; the less sensitive lead salts cover this region. Cryogenically cooled MCT detectors can cover the region of 1.0–2.5μm. * Mid-wave infrared: 3 to 5 μm (defined by the atmospheric window and covered by
indium antimonide Indium antimonide (InSb) is a crystalline compound made from the elements indium Indium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, ...

indium antimonide
, InSb and mercury cadmium telluride, HgCdTe, and partially by
lead selenide Lead selenide (PbSe), or lead(II) selenide, a selenide of lead Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most commo ...
, PbSe). * Long-wave infrared: 8 to 12, or 7 to 14 μm (this is the atmospheric window covered by HgCdTe and
microbolometer A microbolometer is a specific type of bolometer used as a detector in a thermal camera. Infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is ...

microbolometer
s). * Very-long wave infrared (VLWIR) (12 to about 30 μm, covered by doped silicon). Near-infrared is the region closest in wavelength to the radiation detectable by the human eye. mid- and
far-infrared 300px, Diagram of part of the electromagnetic spectrum Far infrared (FIR) is a region in the infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. I ...
are progressively further from the
visible spectrum The visible spectrum is the portion of the that is to the . in this range of s is called ' or simply . A typical will respond to wavelengths from about 380 to about 750 . In terms of frequency, this corresponds to a band in the vicinity of ...
. Other definitions follow different physical mechanisms (emission peaks, vs. bands, water absorption) and the newest follow technical reasons (the common
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...

silicon
detectors are sensitive to about 1,050 nm, while
InGaAs Indium gallium arsenide (InGaAs) (alternatively gallium indium arsenide, GaInAs) is a ternary alloy (chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and genera ...
's sensitivity starts around 950 nm and ends between 1,700 and 2,600 nm, depending on the specific configuration). No international standards for these specifications are currently available. The onset of infrared is defined (according to different standards) at various values typically between 700 nm and 800 nm, but the boundary between visible and infrared light is not precisely defined. The human eye is markedly less sensitive to light above 700 nm wavelength, so longer wavelengths make insignificant contributions to scenes illuminated by common light sources. However, particularly intense near-IR light (e.g., from IR
laser A laser is a device that emits light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as h ...

laser
s, IR LED sources, or from bright daylight with the visible light removed by colored gels) can be detected up to approximately 780 nm, and will be perceived as red light. Intense light sources providing wavelengths as long as 1,050 nm can be seen as a dull red glow, causing some difficulty in near-IR illumination of scenes in the dark (usually this practical problem is solved by indirect illumination). Leaves are particularly bright in the near IR, and if all visible light leaks from around an IR-filter are blocked, and the eye is given a moment to adjust to the extremely dim image coming through a visually opaque IR-passing photographic filter, it is possible to see the Wood effect that consists of IR-glowing foliage.


Telecommunication bands in the infrared

In
optical communications Optical communication, also known as optical telecommunication, is communication Communication (from Latin ''communicare'', meaning "to share") is the act of developing Semantics, meaning among Subject (philosophy), entities or Organization, gr ...
, the part of the infrared spectrum that is used is divided into seven bands based on availability of light sources transmitting/absorbing materials (fibers) and detectors: The C-band is the dominant band for long-distance
telecommunication Telecommunication is the transmission of information by various types of technologies over wire A wire is a single usually cylindrical A cylinder (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Gr ...
networks. The S and L bands are based on less well established technology, and are not as widely deployed.


Heat

Infrared radiation is popularly known as "heat radiation", but light and electromagnetic waves of any frequency will heat surfaces that absorb them. Infrared light from the Sun accounts for 49% of the heating of Earth, with the rest being caused by visible light that is absorbed then re-radiated at longer wavelengths. Visible light or
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, ...

ultraviolet
-emitting
laser A laser is a device that emits light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as h ...

laser
s can char paper and incandescently hot objects emit visible radiation. Objects at room
temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy refers to several distinct physical concept ...

temperature
will emit
radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and f ...
concentrated mostly in the 8 to 25 μm band, but this is not distinct from the emission of visible light by incandescent objects and ultraviolet by even hotter objects (see
black body A black body or blackbody is an idealized physical object, physical body that absorption (electromagnetic radiation), absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence (optics), angle of incidence. The ...

black body
and
Wien's displacement law upright=1.45, Black-body radiation as a function of wavelength for various temperatures. Each temperature curve peaks at a different wavelength and Wien's law describes the shift of that peak. Wien's displacement law states that the black-body r ...
).
Heat In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these ...

Heat
is energy in transit that flows due to a temperature difference. Unlike heat transmitted by
thermal conduction Thermal conduction is the transfer of by microscopic collisions of particles and movement of electrons within a body. The colliding particles, which include molecules, atoms and electrons, transfer disorganized microscopic kinetic and potential en ...

thermal conduction
or
thermal convection Convection (or convective heat transfer) is the transfer of heat from one place to another due to the movement of fluid. Although often discussed as a distinct method of heat transfer, convective heat transfer involves the combined processes of ...
, thermal radiation can propagate through a
vacuum A vacuum is a space Space is the boundless three-dimensional Three-dimensional space (also: 3-space or, rarely, tri-dimensional space) is a geometric setting in which three values (called parameter A parameter (from the Ancient Gr ...

vacuum
. Thermal radiation is characterized by a particular spectrum of many wavelengths that are associated with emission from an object, due to the vibration of its molecules at a given temperature. Thermal radiation can be emitted from objects at any wavelength, and at very high temperatures such radiation is associated with spectra far above the infrared, extending into visible, ultraviolet, and even X-ray regions (e.g. the
solar corona A corona (, in turn derived from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the f ...
). Thus, the popular association of infrared radiation with thermal radiation is only a coincidence based on typical (comparatively low) temperatures often found near the surface of planet Earth. The concept of
emissivity The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation Thermal radiation is electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementar ...
is important in understanding the infrared emissions of objects. This is a property of a surface that describes how its thermal emissions deviate from the idea of a
black body A black body or blackbody is an idealized physical object, physical body that absorption (electromagnetic radiation), absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence (optics), angle of incidence. The ...

black body
. To further explain, two objects at the same physical temperature may not show the same infrared image if they have differing emissivity. For example, for any pre-set emissivity value, objects with higher emissivity will appear hotter, and those with a lower emissivity will appear cooler (assuming, as is often the case, that the surrounding environment is cooler than the objects being viewed). When an object has less than perfect emissivity, it obtains properties of reflectivity and/or transparency, and so the temperature of the surrounding environment is partially reflected by and/or transmitted through the object. If the object were in a hotter environment, then a lower emissivity object at the same temperature would likely appear to be hotter than a more emissive one. For that reason, incorrect selection of emissivity and not accounting for environmental temperatures will give inaccurate results when using infrared cameras and pyrometers.


Applications


Night vision

Infrared is used in night vision equipment when there is insufficient
visible light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nano ...
to see.
Night vision devices A standard M110. Note that in addition to the image intensifier, the NVD gathers much more light by its much larger aperture A night-vision device (NVD), also known as night optical/observation device (NOD) and night-vision goggles (NVG), is a ...
operate through a process involving the conversion of ambient light photons into electrons that are then amplified by a chemical and electrical process and then converted back into visible light. Infrared light sources can be used to augment the available ambient light for conversion by night vision devices, increasing in-the-dark visibility without actually using a visible light source. The use of infrared light and night vision devices should not be confused with
thermal imaging Infrared thermography (IRT), thermal video and/or thermal imaging, is a process where a thermal camera A thermographic camera (also called an infrared camera or thermal imaging camera or thermal imager) is a device that creates an image using ...
, which creates images based on differences in surface temperature by detecting infrared radiation (
heat In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these ...

heat
) that emanates from objects and their surrounding environment.


Thermography

Infrared radiation can be used to remotely determine the temperature of objects (if the emissivity is known). This is termed thermography, or in the case of very hot objects in the NIR or visible it is termed
pyrometry A pyrometer is a type of remote-sensing thermometer used to measure the temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be ...
. Thermography (thermal imaging) is mainly used in military and industrial applications but the technology is reaching the public market in the form of infrared cameras on cars due to greatly reduced production costs. Thermographic cameras detect radiation in the infrared range of the electromagnetic spectrum (roughly 9,000–14,000 nanometers or 9–14 μm) and produce images of that radiation. Since infrared radiation is emitted by all objects based on their temperatures, according to the black-body radiation law, thermography makes it possible to "see" one's environment with or without visible illumination. The amount of radiation emitted by an object increases with temperature, therefore thermography allows one to see variations in temperature (hence the name).


Hyperspectral imaging

A hyperspectral image is a "picture" containing continuous
spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum Continuum may refer to: * Continuum (measurement) Continuum theories or models expla ...

spectrum
through a wide spectral range at each pixel. Hyperspectral imaging is gaining importance in the field of applied spectroscopy particularly with NIR, SWIR, MWIR, and LWIR spectral regions. Typical applications include biological, mineralogical, defence, and industrial measurements. Thermal infrared hyperspectral imaging can be similarly performed using a
thermographic camera A thermographic camera (also called an infrared camera or thermal imaging camera, thermal camera or thermal imager) is a device that creates an image using infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation ...

thermographic camera
, with the fundamental difference that each pixel contains a full LWIR spectrum. Consequently, chemical identification of the object can be performed without a need for an external light source such as the Sun or the Moon. Such cameras are typically applied for geological measurements, outdoor surveillance and
UAV , a hunter-killer surveillance UAV , rotorcraft A rotorcraft or rotary-wing aircraft is a heavier-than-air aircraft An aircraft is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters th ...
applications.Frost&Sullivan, Technical Insights, Aerospace&Defence (Feb 2011)
World First Thermal Hyperspectral Camera for Unmanned Aerial Vehicles


Other imaging

In
infrared photography ''Top:'' tree photographed in the near infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR ...
,
infrared filter Infrared cut-off filters, sometimes called IR filters or heat-absorbing filters, are designed to reflect or block near-infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than th ...
s are used to capture the near-infrared spectrum.
Digital camera A digital camera is a camera A camera is an optical Optics is the branch of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behav ...

Digital camera
s often use infrared blockers. Cheaper digital cameras and
camera phones A camera phone is a mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, or hand phone, sometimes shortened to simply mobile, cell or just phone, is a portable telephone A telephone is a telecommunicatio ...
have less effective filters and can "see" intense near-infrared, appearing as a bright purple-white color. This is especially pronounced when taking pictures of subjects near IR-bright areas (such as near a lamp), where the resulting infrared interference can wash out the image. There is also a technique called '
T-ray Terahertz radiation – also known as submillimeter radiation, terahertz waves, tremendously high frequency (THF), T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic wave Electromagnetism is a branch of physic ...
' imaging, which is imaging using
far-infrared 300px, Diagram of part of the electromagnetic spectrum Far infrared (FIR) is a region in the infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. I ...
or
terahertz radiation Terahertz radiation – also known as submillimeter radiation, terahertz waves, tremendously high frequency (THF), T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic wave Electromagnetism is a branch of physic ...
. Lack of bright sources can make terahertz photography more challenging than most other infrared imaging techniques. Recently T-ray imaging has been of considerable interest due to a number of new developments such as
terahertz time-domain spectroscopy In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), motion and behavior through Sp ...
.


Tracking

Infrared tracking, also known as infrared homing, refers to a passive missile guidance system, which uses the emission from a target of
electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. ...

electromagnetic radiation
in the infrared part of the
spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum Continuum may refer to: * Continuum (measurement) Continuum theories or models expla ...

spectrum
to track it. Missiles that use infrared seeking are often referred to as "heat-seekers" since infrared (IR) is just below the visible spectrum of light in frequency and is radiated strongly by hot bodies. Many objects such as people, vehicle engines, and aircraft generate and retain heat, and as such, are especially visible in the infrared wavelengths of light compared to objects in the background.


Heating

Infrared radiation can be used as a deliberate heating source. For example, it is used in
infrared sauna An Infrared Sauna is a type of sauna that uses infrared heaters to emit infrared light experienced as thermal radiation, radiant heat which is absorbed by the surface of the skin. Infrared saunas are popular in Alternative medicine, alternative ...
s to heat the occupants. It may also be used in other heating applications, such as to remove ice from the wings of aircraft (de-icing). Infrared radiation is used in cooking, known as broiling or
grilling Grilling is a form of cooking Cooking, cookery, or culinary arts is the art, science, and craft of using heat In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynam ...

grilling
. One energy advantage is that the IR energy heats only opaque objects, such as food, rather than the air around them. Infrared heating is also becoming more popular in industrial manufacturing processes, e.g. curing of coatings, forming of plastics, annealing, plastic welding, and print drying. In these applications, infrared heaters replace convection ovens and contact heating. Efficiency is achieved by matching the wavelength of the infrared heater to the absorption characteristics of the material.


Cooling

A variety of technologies or proposed technologies take advantage of infrared emissions to cool buildings or other systems. The LWIR (8–15 μm) region is especially useful since some radiation at these wavelengths can escape into space through the atmosphere.


Communications

IR data transmission is also employed in short-range communication among computer peripherals and
personal digital assistant#REDIRECT Personal digital assistant The Palm TX A personal digital assistant (PDA), also known as a handheld PC, is a variety mobile device which functions as a personal information manager. PDAs have been mostly displaced by the widesprea ...
s. These devices usually conform to standards published by
IrDA The Infrared Data Association (IrDA) is an industry-driven interest group that was founded in 1994 by around 50 companies. IrDA provides specifications for a complete set of protocols for wireless infrared communications, and the name "IrDA" also ...
, the Infrared Data Association. Remote controls and IrDA devices use infrared
light-emitting diode A light-emitting diode (LED) is a semiconductor A semiconductor material has an value falling between that of a , such as metallic copper, and an , such as glass. Its falls as its temperature rises; metals behave in the opposite ...
s (LEDs) to emit infrared radiation that may be concentrated by a
lens A lens is a transmissive optical Optics is the branch of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, s ...

lens
into a beam that the user aims at the detector. The beam is
modulated In electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. It uses active devices to control electron flow by amplifier, amplifi ...
, i.e. switched on and off, according to a code which the receiver interprets. Usually very near-IR is used (below 800 nm) for practical reasons. This wavelength is efficiently detected by inexpensive
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...

silicon
photodiode A photodiode is a semiconductor p–n junction device that converts light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the human eye. Visib ...

photodiode
s, which the receiver uses to convert the detected radiation to an
electric current An electric current is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, ...
. That electrical signal is passed through a
high-pass filter A high-pass filter (HPF) is an electronic filter that passes signals with a frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also referred to as temporal frequency, which emphasizes the contrast ...

high-pass filter
which retains the rapid pulsations due to the IR transmitter but filters out slowly changing infrared radiation from ambient light. Infrared communications are useful for indoor use in areas of high population density. IR does not penetrate walls and so does not interfere with other devices in adjoining rooms. Infrared is the most common way for
remote control In electronics, a remote control (also known as a remote or clicker) is an electronic device used to operate another device from a distance, usually wirelessly. In consumer electronics, a remote control can be used to operate devices such as ...

remote control
s to command appliances. Infrared remote control protocols like
RC-5 The RC-5 protocol was developed by Philips Koninklijke Philips N.V. (in Dutch Dutch commonly refers to: * Something of, from, or related to the Netherlands * Dutch people () * Dutch language () *Dutch language , spoken in Belgium (also re ...
, SIRC, are used to communicate with infrared. Free space optical communication using infrared
laser A laser is a device that emits light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as h ...

laser
s can be a relatively inexpensive way to install a communications link in an urban area operating at up to 4 gigabit/s, compared to the cost of burying fiber optic cable, except for the radiation damage. "Since the eye cannot detect IR, blinking or closing the eyes to help prevent or reduce damage may not happen." Infrared lasers are used to provide the light for
optical fiber An optical fiber (or fibre in British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codificati ...

optical fiber
communications systems. Infrared light with a wavelength around 1,330 nm (least
dispersion Dispersion may refer to: Economics and finance *Dispersion (finance), a measure for the statistical distribution of portfolio returns *Price dispersion, a variation in prices across sellers of the same item *Wage dispersion, the amount of variation ...
) or 1,550 nm (best transmission) are the best choices for standard
silica Silicon dioxide, also known as silica, is an oxide An oxide () is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any su ...

silica
fibers. IR data transmission of encoded audio versions of printed signs is being researched as an aid for visually impaired people through the RIAS (Remote Infrared Audible Signage) project. Transmitting IR data from one device to another is sometimes referred to as beaming.


Spectroscopy

(see also
near-infrared spectroscopy showing complicated overlapping overtones of mid IR absorption features. Near-infrared spectroscopy (NIRS) is a spectroscopic Spectroscopy is the study of the interaction between matter In classical physics and general chemistry, matter is ...
) is a technique that can be used to identify molecules by analysis of their constituent bonds. Each chemical bond in a molecule vibrates at a frequency characteristic of that bond. A group of atoms in a molecule (e.g., CH2) may have multiple modes of oscillation caused by the stretching and bending motions of the group as a whole. If an oscillation leads to a change in
dipole In electromagnetism Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electric charge, electrically charged particles. The electromagnetic force is c ...

dipole
in the molecule then it will absorb a
photon The photon ( el, φῶς, phōs, light) is a type of elementary particle In , an elementary particle or fundamental particle is a that is not composed of other particles. Particles currently thought to be elementary include the fundamental s ...

photon
that has the same frequency. The vibrational frequencies of most molecules correspond to the frequencies of infrared light. Typically, the technique is used to study
organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s using light radiation from the mid-infrared, 4,000–400 cm−1. A spectrum of all the frequencies of absorption in a sample is recorded. This can be used to gain information about the sample composition in terms of chemical groups present and also its purity (for example, a wet sample will show a broad O-H absorption around 3200 cm−1). The unit for expressing radiation in this application, cm−1, is the spectroscopic
wavenumber In the physical science Physical science is a branch of natural science that studies non-living systems, in contrast to life science. It in turn has many branches, each referred to as a "physical science", together called the "physical scienc ...
. It is the frequency divided by the speed of light in vacuum.


Thin film metrology

In the semiconductor industry, infrared light can be used to characterize materials such as thin films and periodic trench structures. By measuring the reflectance of light from the surface of a semiconductor wafer, the index of refraction (n) and the extinction Coefficient (k) can be determined via the Forouhi-Bloomer dispersion equations. The reflectance from the infrared light can also be used to determine the critical dimension, depth, and sidewall angle of high aspect ratio trench structures.


Meteorology

Weather satellite A weather satellite alt=, A full-size model of the Earth observation satellite ERS 2 ">ERS_2.html" ;"title="Earth observation satellite ERS 2">Earth observation satellite ERS 2 In the context of spaceflight, a satellite is an object that ...
s equipped with scanning radiometers produce thermal or infrared images, which can then enable a trained analyst to determine cloud heights and types, to calculate land and surface water temperatures, and to locate ocean surface features. The scanning is typically in the range 10.3–12.5 μm (IR4 and IR5 channels). Clouds with high and cold tops, such as
cyclone In meteorology Meteorology is a branch of the (which include and ), with a major focus on . The study of meteorology dates back , though significant progress in meteorology did not begin until the 18th century. The 19th century saw mo ...

cyclone
s or
cumulonimbus cloud Cumulonimbus (from Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republ ...

cumulonimbus cloud
s, are often displayed as red or black, lower warmer clouds such as or
stratocumulus A stratocumulus cloud, occasionally called a cumulostratus, belongs to a genus-type of clouds characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in Altocumulus cloud, alt ...

stratocumulus
are displayed as blue or grey, with intermediate clouds shaded accordingly. Hot land surfaces are shown as dark-grey or black. One disadvantage of infrared imagery is that low cloud such as stratus or
fog Fog is a visible aerosol consisting of tiny water drop (liquid), droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus cloud, s ...

fog
can have a temperature similar to the surrounding land or sea surface and does not show up. However, using the difference in brightness of the IR4 channel (10.3–11.5 μm) and the near-infrared channel (1.58–1.64 μm), low cloud can be distinguished, producing a ''fog'' satellite picture. The main advantage of infrared is that images can be produced at night, allowing a continuous sequence of weather to be studied. These infrared pictures can depict ocean eddies or vortices and map currents such as the Gulf Stream, which are valuable to the shipping industry. Fishermen and farmers are interested in knowing land and water temperatures to protect their crops against frost or increase their catch from the sea. Even
El Niño es, El Niño, translation=The Boy (; ) is the warm phase of the El Niño–Southern Oscillation El Niño–Southern Oscillation (ENSO) is an irregular periodic variation in winds and sea surface temperatures over the Tropics, tropical easte ...
phenomena can be spotted. Using color-digitized techniques, the gray-shaded thermal images can be converted to color for easier identification of desired information. The main water vapour channel at 6.40 to 7.08 μm can be imaged by some weather satellites and shows the amount of moisture in the atmosphere.


Climatology

In the field of climatology, atmospheric infrared radiation is monitored to detect trends in the energy exchange between the earth and the atmosphere. These trends provide information on long-term changes in Earth's climate. It is one of the primary parameters studied in research into
global warming Contemporary climate change includes both the global warming caused by humans, and its impacts on Earth's weather patterns. There have been previous periods of climate change, but the current changes are more rapid than any known even ...

global warming
, together with
solar radiation Solar irradiance is the power Power typically refers to: * Power (physics) In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equal to one j ...
. A is utilized in this field of research to perform continuous outdoor measurements. This is a broadband infrared radiometer with sensitivity for infrared radiation between approximately 4.5 μm and 50 μm.


Astronomy

Astronomers observe objects in the infrared portion of the electromagnetic spectrum using optical components, including mirrors, lenses and solid state digital detectors. For this reason it is classified as part of
optical astronomy Visible-light astronomy encompasses a wide variety of observation Observation is the active acquisition of information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus ...
. To form an image, the components of an infrared telescope need to be carefully shielded from heat sources, and the detectors are chilled using liquid
helium Helium (from el, ἥλιος, helios Helios; Homeric Greek: ), Latinized as Helius; Hyperion and Phaethon are also the names of his father and son respectively. often given the epithets Hyperion ("the one above") and Phaethon ("the shining" ...

helium
. The sensitivity of Earth-based infrared telescopes is significantly limited by water vapor in the atmosphere, which absorbs a portion of the infrared radiation arriving from space outside of selected atmospheric windows. This limitation can be partially alleviated by placing the telescope observatory at a high altitude, or by carrying the telescope aloft with a balloon or an aircraft. Space telescopes do not suffer from this handicap, and so outer space is considered the ideal location for infrared astronomy. The infrared portion of the spectrum has several useful benefits for astronomers. Cold, dark
molecular cloud A molecular cloud, sometimes called a stellar nursery (if star formation is occurring within), is a type of interstellar cloud, the density and size of which permit absorption nebulae, the formation of molecules (most commonly molecular hydrogen, ...
s of gas and dust in our galaxy will glow with radiated heat as they are irradiated by imbedded stars. Infrared can also be used to detect
protostar A protostar is a very young star that is still gathering mass from its parent molecular cloud. The protostellar phase is the earliest one in the process of stellar evolution. For a low mass star (i.e. that of the Sun or lower), it lasts about 5 ...
s before they begin to emit visible light. Stars emit a smaller portion of their energy in the infrared spectrum, so nearby cool objects such as
planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and ...

planet
s can be more readily detected. (In the visible light spectrum, the glare from the star will drown out the reflected light from a planet.) Infrared light is also useful for observing the cores of active galaxies, which are often cloaked in gas and dust. Distant galaxies with a high
redshift In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular ...

redshift
will have the peak portion of their spectrum shifted toward longer wavelengths, so they are more readily observed in the infrared.


Infrared cleaning

Infrared cleaning Infrared cleaning is a technique used by some film scanners and flatbed scanners to reduce or remove the effect of dust and scratches upon the finished scan. It works by collecting an additional infrared Infrared (IR), sometimes called infra ...
is a technique used by some
motion picture film scanner A motion picture film scanner is a device used in Digital data, digital filmmaking to scan original Photographic film, film for storage as high-resolution digital intermediate files. A film scanner scans original film stock: negative or positive p ...
s,
film scanner CanoScan9950F, a flatbed scanner that can also scan film A film scanner is a device made for Image scanning, scanning photographic film directly into a computer without the use of any intermediate printmaking. It provides several benefits over u ...
s and
flatbed scanner An image scanner—often abbreviated to just scanner, is a device that optically scans images, printed text, handwriting or an object and converts it to a digital image. Commonly used in offices are variations of the desktop ''flatbed scanner'' w ...
s to reduce or remove the effect of dust and scratches upon the finished
scan Scan may refer to: Acronyms *Schedules for Clinical Assessment in Neuropsychiatry (SCAN), a psychiatric diagnostic tool developed by WHO *Shared Check Authorization Network (SCAN), a database of bad check writers and collection agency for bad chec ...
. It works by collecting an additional infrared channel from the scan at the same position and resolution as the three visible color channels (red, green, and blue). The infrared channel, in combination with the other channels, is used to detect the location of scratches and dust. Once located, those defects can be corrected by scaling or replaced by
inpainting Image:Restoration.jpg, 350px, Original and restored image Inpainting is a Art conservation, conservation process where damaged, deteriorating, or missing parts of an artwork are filled in to present a complete image. This process can be applied to ...
.


Art conservation and analysis

Infrared reflectography can be applied to paintings to reveal underlying layers in a non-destructive manner, in particular the artist's
underdrawing Underdrawing is a preparatory drawing Drawing is a form of visual art The visual arts are art forms such as painting Painting is the practice of applying paint, pigment, color or other medium to a solid surface (called the "matrix" ...
or outline drawn as a guide. Art conservators use the technique to examine how the visible layers of paint differ from the underdrawing or layers in between (such alterations are called
pentimenti A pentimento (plural pentimenti), in painting 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 o ...

pentimenti
when made by the original artist). This is very useful information in deciding whether a painting is the
prime version In the art world, if an artwork exists in several versions, the one known or believed to be the earliest is called the prime version. Many artworks produced in media such as painting Painting is the practice of applying paint, pigment, co ...
by the original artist or a copy, and whether it has been altered by over-enthusiastic restoration work. In general, the more pentimenti, the more likely a painting is to be the prime version. It also gives useful insights into working practices. Reflectography often reveals the artist's use of
carbon black Carbon black (subtypes are acetylene black, channel black, furnace black, lamp black and thermal black) is a material produced by the incomplete combustion of heavy petroleum Petroleum, also known as crude oil and oil, is a naturally occ ...

carbon black
, which shows up well in reflectograms, as long as it has not also been used in the ground underlying the whole painting. Recent progress in the design of infrared-sensitive cameras makes it possible to discover and depict not only underpaintings and pentimenti, but entire paintings that were later overpainted by the artist. Notable examples are
Picasso Pablo Ruiz Picasso (25 October 1881 – 8 April 1973) was a Spanish painter, sculptor, printmaker, ceramicist and Scenic design, theatre designer who spent most of his adult life in France. Regarded as one of the most influential artists of ...

Picasso
's '' Woman Ironing'' and ''Blue Room (Picasso), Blue Room'', where in both cases a portrait of a man has been made visible under the painting as it is known today. Similar uses of infrared are made by conservators and scientists on various types of objects, especially very old written documents such as the Dead Sea Scrolls, the Roman works in the Villa of the Papyri, and the Silk Road texts found in the Mogao Caves, Dunhuang Caves. Carbon black used in ink can show up extremely well.


Biological systems

The Crotalinae, pit viper has a pair of infrared sensory pits on its head. There is uncertainty regarding the exact thermal sensitivity of this biological infrared detection system. Other organisms that have thermoreceptive organs are pythons (family Pythonidae), some boas (family Boidae), the Common Vampire Bat (''Desmodus rotundus''), a variety of jewel beetles (''Melanophila acuminata''), darkly pigmented butterflies (''Pachliopta aristolochiae'' and ''Troides rhadamantus plateni''), and possibly blood-sucking bugs (''Triatoma infestans''). Some fungi like ''Venturia inaequalis'' require near-infrared light for ejection Although near-infrared vision (780–1,000 nm) has long been deemed impossible due to noise in visual pigments, sensation of near-infrared light was reported in the common carp and in three cichlid species. Fish use NIR to capture prey and for phototactic swimming orientation. NIR sensation in fish may be relevant under poor lighting conditions during twilight and in turbid surface waters.


Photobiomodulation

Near-infrared light, or photobiomodulation, is used for treatment of chemotherapy-induced oral ulceration as well as wound healing. There is some work relating to anti-herpes virus treatment. Research projects include work on central nervous system healing effects via cytochrome c oxidase upregulation and other possible mechanisms.


Health hazards

Strong infrared radiation in certain industry high-heat settings may be hazardous to the eyes, resulting in damage or blindness to the user. Since the radiation is invisible, special IR-proof goggles must be worn in such places.


History of infrared science

The discovery of infrared radiation is ascribed to
William Herschel Sir Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a spe ...

William Herschel
, the astronomer, in the early 19th century. Herschel published his results in 1800 before the Royal Society of London. Herschel used a Triangular prism (optics), prism to refract light from the sun and detected the infrared, beyond the
red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength Image:dominant wavelength.png, frame, Dominant/complementary wavelength example on the CIE color ...

red
part of the spectrum, through an increase in the temperature recorded on a
thermometer (mercury-in-glass thermometer) for measurement of room temperature. A thermometer is a device that temperature measurement, measures temperature or a temperature gradient A temperature gradient is a physical quantity that describes in which dir ...

thermometer
. He was surprised at the result and called them "Calorific Rays". The term "infrared" did not appear until late 19th century. Other important dates include: * 1830: Leopoldo Nobili made the first thermopile IR detector. * 1840: John Herschel produces the first thermal image, called a thermogram. * 1860: Gustav Kirchhoff formulated the Kirchhoff's law of thermal radiation, blackbody theorem E = J(T, n). * 1873: Willoughby Smith discovered the photoconductivity of selenium. * 1878: Samuel Pierpont Langley invents the first bolometer, a device which is able to measure small temperature fluctuations, and thus the power of far infrared sources. * 1879: Stefan–Boltzmann law formulated empirically that the power radiated by a blackbody is proportional to ''T''4. * 1880s and 1890s: John Strutt, 3rd Baron Rayleigh, Lord Rayleigh and Wilhelm Wien solved part of the blackbody equation, but both solutions diverged in parts of the electromagnetic spectrum. This problem was called the "ultraviolet catastrophe and infrared catastrophe". * 1892: Willem Henri Julius published infrared spectra of 20 organic compounds measured with a bolometer in units of angular displacement. * 1901: Max Planck published the Planck's law, blackbody equation and theorem. He solved the problem by quantizing the allowable energy transitions. * 1905: Albert Einstein developed the theory of the photoelectric effect. * 1905–1908: William Coblentz published infrared spectra in units of wavelength (micrometers) for several chemical compounds in ''Investigations of Infra-Red Spectra''. * 1917: Theodore Case developed the thallous sulfide detector; British scientist built the first infra-red search and track (IRST) device able to detect aircraft at a range of one mile (1.6 km). * 1935: Lead salts – early missile guidance in World War II. * 1938: Yeou Ta predicted that the pyroelectric effect could be used to detect infrared radiation. * 1945: The Zielgerät 1229 "Vampir" infrared weapon system was introduced as the first portable infrared device for military applications. * 1952: Heinrich Welker grew synthetic Indium antimonide, InSb crystals. * 1950s and 1960s: Nomenclature and radiometric units defined by Fred Nicodemenus, G. J. Zissis and R. Clark; Robert Clark Jones defined ''D''*. * 1958: W. D. Lawson (Royal Radar Establishment in Malvern) discovered IR detection properties of Mercury cadmium telluride (HgCdTe). * 1958: AIM-4 Falcon, Falcon and AIM-9 Sidewinder, Sidewinder missiles were developed using infrared technology. * 1960s: Paul Kruse (engineer), Paul Kruse and his colleagues at Honeywell, Honeywell Research Center demonstrate the use of HgCdTe as an effective chemical compound, compound for infrared detection. * 1962: J. Cooper demonstrated pyroelectric detection. * 1964: W. G. Evans discovered infrared thermoreceptors in a pyrophile beetle. * 1965: First IR handbook; first commercial imagers (Barnes, Agema (now part of FLIR Systems Inc.)); Richard Hudson (physicist), Richard Hudson's landmark text; F4 TRAM FLIR by Hughes Aircraft Company, Hughes; phenomenology pioneered by Fred Simmons (scientist), Fred Simmons and A. T. Stair; U.S. Army's night vision lab formed (now Night Vision and Electronic Sensors Directorate (NVESD)), and Rachets develops detection, recognition and identification modeling there. * 1970: Willard Boyle and George E. Smith proposed CCD at Bell Labs for picture phone. * 1973: Common module program started by NVESD. * 1978: Infrared imaging astronomy came of age, observatories planned, NASA Infrared Telescope Facility, IRTF on Mauna Kea opened; 32 × 32 and 64 × 64 arrays produced using InSb, HgCdTe and other materials. * 2013: On 14 February, researchers developed a neural implant that gives rats the ability to sense infrared light, which for the first time provides living creatures with new abilities, instead of simply replacing or augmenting existing abilities.


See also


Notes


References


External links


Infrared: A Historical Perspective
(Omega Engineering)
Infrared Data Association
a standards organization for infrared data interconnection



* [https://web.archive.org/web/20060114051647/http://imagers.gsfc.nasa.gov/ems/infrared.html Infrared Waves]: detailed explanation of infrared light. (NASA)
Herschel's original paper from 1800 announcing the discovery of infrared light

The thermographic's library
collection of thermogram
Infrared reflectography in analysis of paintings
at ColourLex * Molly Faries
Techniques and Applications – Analytical Capabilities of Infrared Reflectography: An Art Historian s Perspective
in Scientific Examination of Art: Modern Techniques in Conservation and Analysis, Sackler NAS Colloquium, 2005 {{DEFAULTSORT:Infrared Infrared, Electromagnetic spectrum