Editing Infrared (section)

== Applications ==

=== Night vision ===

{{Main|Night vision}}
[[File:Active-Infrared-Night-Vision.jpg|thumb|Active-infrared night vision: the camera illuminates the scene at infrared wavelengths invisible to the [[human eye]]. Despite a dark back-lit scene, active-infrared night vision delivers identifying details, as seen on the display monitor.]] Infrared is used in night vision equipment when there is insufficient visible light to see.<ref name="how night vision works">{{Cite web |title=How Night Vision Works |url=http://www.atncorp.com/HowNightVisionWorks |url-status=live |archive-url=https://web.archive.org/web/20150824223644/http://www.atncorp.com/hownightvisionworks |archive-date=2015-08-24 |access-date=2007-08-12 |publisher=American Technologies Network Corporation}}</ref> [[Night vision devices]] 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.<ref name="how night vision works" /> 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.<ref name="how night vision works" /><ref name="Vatansever-2012">{{Cite journal |last=Vatansever |first=Fatma |last2=Hamblin |first2=Michael R. |date=2012-01-01 |title=Far infrared radiation (FIR): Its biological effects and medical applications |journal=Photonics & Lasers in Medicine |volume=1 |issue=4 |pages=255–266 |doi=10.1515/plm-2012-0034 |issn=2193-0643 |pmc=3699878 |pmid=23833705}}</ref>

The use of infrared light and night vision devices should not be confused with [[thermal imaging]], which creates images based on differences in surface temperature by detecting infrared radiation ([[heat]]) that emanates from objects and their surrounding environment.<ref>{{Cite web |last=Bryant |first=Lynn |date=2007-06-11 |title=How does thermal imaging work? A closer look at what is behind this remarkable technology |url=http://www.video-surveillance-guide.com/how-does-thermal-imaging-work.htm |url-status=dead |archive-url=https://web.archive.org/web/20070728055934/http://www.video-surveillance-guide.com/how-does-thermal-imaging-work.htm |archive-date=2007-07-28 |access-date=2007-08-12}}</ref><ref name="Michael Rowan" />

=== Thermography ===

[[File:STS-3 infrared on reentry.jpg|thumb|left|upright=0.7|Thermography helped to determine the temperature profile of the [[Space Shuttle thermal protection system]] during re-entry.]]{{Main|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]]. 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 nm or 9–14&nbsp;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 ===

{{Main|Hyperspectral imaging}}

[[File:Specim aisaowl outdoor.png|thumb|left| Hyperspectral thermal infrared [[Emission spectrum|emission]] measurement, an outdoor scan in winter conditions, ambient temperature −15&nbsp;°C, image produced with a [[Specim]] LWIR hyperspectral imager. Relative radiance spectra from various targets in the image are shown with arrows. The [[infrared spectra]] of the different objects such as the watch clasp have clearly distinctive characteristics. The contrast level indicates the temperature of the object.<ref name="Holma">Holma, H., (May 2011), [http://www.photonik.de/index.php?id=11&np=5&artid=848&L=1 Thermische Hyperspektralbildgebung im langwelligen Infrarot] {{webarchive|url=https://web.archive.org/web/20110726171326/http://www.photonik.de/index.php?id=11&np=5&artid=848&L=1 |date=2011-07-26 }}, Photonik</ref>]]
[[File:Blue infrared light.jpg|thumb|Infrared light from the [[LED]] of a [[remote control]] as recorded by a digital camera]]

A hyperspectral image is a "picture" containing continuous [[Infrared spectroscopy|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]], 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]] applications.<ref name="Frost&Sullivan Specim Owl">Frost&Sullivan, Technical Insights, Aerospace&Defence (Feb 2011): [http://www.frost.com/prod/servlet/segment-toc.pag?segid=D870-00-48-00-00&ctxixpLink=FcmCtx3&ctxixpLabel=FcmCtx4 World First Thermal Hyperspectral Camera for Unmanned Aerial Vehicles] {{Webarchive|url=https://web.archive.org/web/20120310214352/http://www.frost.com/prod/servlet/segment-toc.pag?segid=D870-00-48-00-00&ctxixpLink=FcmCtx3&ctxixpLabel=FcmCtx4 |date=2012-03-10 }}.</ref>

=== Other imaging ===
[[File:Infrared portrait comparison.jpg|thumb|Reflected light photograph in various infrared spectra to illustrate the appearance as the wavelength of light changes]]

In [[infrared photography]], [[infrared filter]]s are used to capture the near-infrared spectrum. [[Digital camera]]s often use infrared [[Filter (optics)|blockers]]. Cheaper digital cameras and [[camera phones]] have less effective filters and can view 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]]' imaging, which is imaging using [[far-infrared]] or [[terahertz radiation]]. 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]].


=== Tracking ===

[[File:FIM-92 seeker DSCN4271.JPG|thumb|The IR seeker head on a [[FIM-92]] [[MANPADS]]]]
{{Main|Infrared homing}}
Infrared tracking, also known as infrared homing, refers to a [[Passive homing|passive missile guidance system]], which uses the [[light emission|emission]] from a target of electromagnetic radiation in the infrared part of the 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.<ref>{{Cite journal |last=Mahulikar, S.P. |last2=Sonawane, H.R. |last3=Rao, G.A. |year=2007 |title=Infrared signature studies of aerospace vehicles |url=http://dspace.library.iitb.ac.in/xmlui/bitstream/handle/10054/613/5740.pdf |url-status=live |journal=Progress in Aerospace Sciences |volume=43 |issue=7–8 |pages=218–245 |bibcode=2007PrAeS..43..218M |citeseerx=10.1.1.456.9135 |doi=10.1016/j.paerosci.2007.06.002 |archive-url=https://web.archive.org/web/20210304165104/http://dspace.library.iitb.ac.in/xmlui/bitstream/handle/10054/613/5740.pdf |archive-date=2021-03-04 |access-date=2013-04-12}}</ref>

=== Heating ===

{{Main|Infrared heating}}
[[File:Hooded dryer for infrared hair drying at hair salon - shown from three perspectives.jpg|thumb|Infrared [[hair dryer]] for [[beauty salon|hair salons]], {{Circa|2010s}}]]
Infrared radiation can be used as a deliberate heating source. For example, it is used in [[infrared sauna]]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).<ref>White, Richard P. (2000) "Infrared deicing system for aircraft" {{US Patent|6092765}}</ref>

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.

=== Cooling ===

{{Main|Passive daytime radiative cooling}}

A variety of technologies or proposed technologies take advantage of infrared emissions to cool buildings or other systems. The LWIR (8–15&nbsp;μm) region is especially useful since some radiation at these wavelengths can escape into space through the atmosphere's [[infrared window]]. This is how [[passive daytime radiative cooling]] (PDRC) surfaces are able to achieve sub-ambient cooling temperatures under direct solar intensity, enhancing terrestrial [[heat flow]] to outer space with zero [[Efficient energy use|energy consumption]] or [[pollution]].<ref>{{Cite journal |last=Chen |first=Meijie |last2=Pang |first2=Dan |last3=Chen |first3=Xingyu |last4=Yan |first4=Hongjie |last5=Yang |first5=Yuan |year=2022 |title=Passive daytime radiative cooling: Fundamentals, material designs, and applications |journal=EcoMat |volume=4 |issue=1 |doi=10.1002/eom2.12153 |s2cid=240331557 |quote=Passive daytime radiative cooling (PDRC) dissipates terrestrial heat to the extremely cold outer space without using any energy input or producing pollution. It has the potential to simultaneously alleviate the two major problems of energy crisis and global warming. |doi-access=free}}</ref><ref>{{Cite journal |last=Munday |first=Jeremy |date=2019 |title=Tackling Climate Change through Radiative Cooling |journal=Joule |volume=3 |issue=9 |pages=2057–2060 |bibcode=2019Joule...3.2057M |doi=10.1016/j.joule.2019.07.010 |s2cid=201590290 |quote=By covering the Earth with a small fraction of thermally emitting materials, the heat flow away from the Earth can be increased, and the net radiative flux can be reduced to zero (or even made negative), thus stabilizing (or cooling) the Earth. |doi-access=free}}</ref> PDRC surfaces maximize shortwave [[solar reflectance]] to lessen heat gain while maintaining strong longwave infrared (LWIR) [[thermal radiation]] [[heat transfer]].<ref>{{Cite journal |last=Wang |first=Tong |last2=Wu |first2=Yi |last3=Shi |first3=Lan |last4=Hu |first4=Xinhua |last5=Chen |first5=Min |last6=Wu |first6=Limin |date=2021 |title=A structural polymer for highly efficient all-day passive radiative cooling |journal=Nature Communications |volume=12 |issue=365 |page=365 |doi=10.1038/s41467-020-20646-7 |pmc=7809060 |pmid=33446648 |quote=Accordingly, designing and fabricating efficient PDRC with sufficiently high solar reflectance (𝜌¯solar) (λ ~ 0.3–2.5 μm) to minimize solar heat gain and simultaneously strong LWIR thermal emittance (ε¯LWIR) to maximize radiative heat loss is highly desirable. When the incoming radiative heat from the Sun is balanced by the outgoing radiative heat emission, the temperature of the Earth can reach its steady state.}}</ref><ref>{{Cite journal |last=Zevenhovena |first=Ron |last2=Fält |first2=Martin |date=June 2018 |title=Radiative cooling through the atmospheric window: A third, less intrusive geoengineering approach |url=https://research.abo.fi/files/25441677/EGY-D-17-05891R1-forArtur.pdf |journal=Energy |volume=152 |page=27 |bibcode=2018Ene...152...27Z |doi=10.1016/j.energy.2018.03.084 |access-date=2022-10-13 |via=Elsevier Science Direct}}</ref> When imagined on a worldwide scale, this cooling method has been proposed as a way to slow and even reverse [[global warming]], with some estimates proposing a global surface area coverage of 1-2% to balance global heat fluxes.<ref>{{Cite journal |last=Munday |first=Jeremy |date=2019 |title=Tackling Climate Change through Radiative Cooling |journal=Joule |volume=3 |issue=9 |pages=2057–2060 |bibcode=2019Joule...3.2057M |doi=10.1016/j.joule.2019.07.010 |s2cid=201590290 |quote=If only 1%–2% of the Earth's surface were instead made to radiate at this rate rather than its current average value, the total heat fluxes into and away from the entire Earth would be balanced and warming would cease. |doi-access=free}}</ref><ref>{{Cite journal |last=Zevenhovena |first=Ron |last2=Fält |first2=Martin |date=June 2018 |title=Radiative cooling through the atmospheric window: A third, less intrusive geoengineering approach |url=https://research.abo.fi/files/25441677/EGY-D-17-05891R1-forArtur.pdf |url-status=live |journal=Energy |volume=152 |pages=27–33 |bibcode=2018Ene...152...27Z |doi=10.1016/j.energy.2018.03.084 |archive-url=https://web.archive.org/web/20241003190747/https://research.abo.fi/files/25441677/EGY-D-17-05891R1-forArtur.pdf |archive-date=2024-10-03 |access-date=2022-10-13 |quote=With 100 W/m2 as a demonstrated passive cooling effect, a surface coverage of 0.3% would then be needed, or 1% of Earth's land mass surface. If half of it would be installed in urban, built areas which cover roughly 3% of the Earth's land mass, a 17% coverage would be needed there, with the remainder being installed in rural areas. |via=Elsevier Science Direct}}</ref>

=== Communications ===

{{Further|Consumer IR}}

IR data transmission is also employed in short-range communication among computer peripherals and [[personal digital assistant]]s. These devices usually conform to standards published by [[IrDA]], the Infrared Data Association. Remote controls and IrDA devices use infrared [[light-emitting diode]]s (LEDs) to emit infrared radiation that may be concentrated by a [[lens]] into a beam that the user aims at the detector. The beam is [[On–off keying|modulated]], i.e. switched on and off, according to a code which the receiver interprets. Usually very near-IR is used (below 800&nbsp;nm) for practical reasons. This wavelength is efficiently detected by inexpensive [[silicon]] [[photodiode]]s, which the receiver uses to convert the detected radiation to an [[electric current]]. That electrical signal is passed through a [[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]]s to command appliances.
Infrared remote control protocols like [[RC-5]], [[Sony Infrared Remote Control|SIRC]], are used to communicate with infrared.

[[Free-space optical communication]] using infrared [[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."<ref>{{Cite web |title=Dangers of Overexposure to ultraviolet, infrared and high-energy visible light |url=http://www.ishn.com/articles/94815-dangers-of-overexposure-to-ultraviolet-infrared-and-high-energy-visible-light |date=2013-01-03 |archive-url=https://web.archive.org/web/20160816163547/http://www.ishn.com/articles/94815-dangers-of-overexposure-to-ultraviolet-infrared-and-high-energy-visible-light |archive-date=2016-08-16 |access-date=2017-04-26 |website=ishn.com – Industrial Safety & Health News}}</ref>

Infrared lasers are used to provide the light for [[optical fiber]] communications systems. Wavelengths around 1,330&nbsp;nm (least [[Dispersion (optics)|dispersion]]) or 1,550&nbsp;nm (best transmission) are the best choices for standard [[silica]] fibers.

IR data transmission of audio versions of printed signs is being researched as an aid for visually impaired people through the [[Remote infrared audible signage]] project.
Transmitting IR data from one device to another is sometimes referred to as [[beaming]].

IR is sometimes used for assistive audio as an alternative to an [[audio induction loop]].

=== Spectroscopy ===

[[Infrared spectroscopy|Infrared vibrational spectroscopy]] (see also [[near-infrared spectroscopy]]) 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., CH<sub>2</sub>) 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 the molecule then it will absorb a [[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]]s using light radiation from the mid-infrared, 4,000–400&nbsp;cm<sup>−1</sup>. 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&nbsp;cm<sup>−1</sup>). The unit for expressing radiation in this application, cm<sup>−1</sup>, is the spectroscopic [[wavenumber]]. 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 model|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 ===

[[File:NOAA Shares First Infrared Imagery from GOES-17 (43904870711).gif|thumb|left|IR satellite picture of cumulonimbus clouds over the [[Great Plains]] of the United States]]
[[Weather satellite]]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&nbsp;μm (IR4 and IR5 channels).

Clouds with high and cold tops, such as [[cyclone]]s or [[cumulonimbus cloud]]s, are often displayed as red or black, lower warmer clouds such as [[Stratus cloud|stratus]] or [[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 clouds such as stratus or [[fog]] can have a temperature similar to the surrounding land or sea surface and do not show up. However, using the difference in brightness of the IR4 channel (10.3–11.5&nbsp;μm) and the near-infrared channel (1.58–1.64&nbsp;μm), low clouds 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]] 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&nbsp;μm can be imaged by some weather satellites and shows the amount of moisture in the atmosphere.
{{clear}}

=== Climatology ===

[[File:Greenhouse-effect-t2.svg|thumb|right|upright=1.55|The [[greenhouse effect]] with molecules of methane, water, and carbon dioxide re-radiating solar heat]]
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]], together with [[solar radiation]].

A [[pyrgeometer]] 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&nbsp;μm and 50&nbsp;μm.

=== Astronomy ===

{{Main|Infrared astronomy|far-infrared astronomy}}
[[File:ESO - Beta Pictoris planet finally imaged (by).jpg|thumb|[[Beta Pictoris]] with its planet Beta Pictoris b, the light-blue dot off-center, as seen in infrared. It combines two images, the inner disc is at 3.6&nbsp;μm.]]
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]]. 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]].

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 [[Infrared window|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]]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]]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]]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]] will have the peak portion of their spectrum shifted toward longer wavelengths, so they are more readily observed in the infrared.<ref name="ir_astronomy" />

=== Cleaning ===

[[Infrared cleaning]] is a technique used by some [[motion picture film scanner]]s, [[film scanner]]s and [[flatbed scanner]]s to reduce or remove the effect of dust and scratches upon the finished [[image scanning|scan]]. 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]].<ref>[https://web.archive.org/web/20110107163528/http://motion.kodak.com/US/en/motion/Products/Lab_And_Post_Production/dice.htm Digital ICE]. kodak.com</ref>

=== Art conservation and analysis ===

[[File:Infrared reflectograms of Mona Lisa.jpg|thumb|left|upright=0.8|An infrared reflectogram of ''[[Mona Lisa]]'' by [[Leonardo da Vinci]]]]
[[File:Infrared reflectography-en.svg|frameless|right|upright=0.9]]
Infrared reflectography<ref>{{Cite web |title=IR Reflectography for Non-destructive Analysis of Underdrawings in Art Objects |url=http://www.sensorsinc.com/artanalysis.html |url-status=dead |archive-url=https://web.archive.org/web/20081208052302/http://www.sensorsinc.com/artanalysis.html |archive-date=2008-12-08 |access-date=2009-02-20 |publisher=Sensors Unlimited, Inc.}}</ref> can be applied to paintings to reveal underlying layers in a non-destructive manner, in particular the artist's [[underdrawing]] 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]] when made by the original artist). This is very useful information in deciding whether a painting is the [[prime version]] 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.<ref>{{Cite web |title=The Mass of Saint Gregory: Examining a Painting Using Infrared Reflectography |url=http://www.clevelandart.org/exhibcef/ConsExhib/html/grien.html |url-status=dead |archive-url=https://web.archive.org/web/20090113225836/http://www.clevelandart.org/exhibcef/ConsExhib/html/grien.html |archive-date=2009-01-13 |access-date=2009-02-20 |publisher=The Cleveland Museum of Art}}</ref> Reflectography often reveals the artist's use of [[carbon black]], which shows up well in reflectograms, as long as it has not also been used in the ground underlying the whole painting. Infrared reflectography can be realized by modified commercial digital cameras in the NIR spectral region or by dedicated instruments in the SWIR spectral region. <ref>{{Cite journal |last=Ambrosini |first=D. |last2=Daffara |first2=C |last3=Di Biase |first3=R. |last4=Paoletti |first4=D. |last5=Pezzati |first5=L. |last6=Bellucci |first6=R. |last7=Bettini |first7=F. |date=13 November 2009 |title=Integrated reflectography and thermography for wooden painting diagnostics |url=https://www.academia.edu/download/92580972/Integrated_reflectography_and_thermography_for_wood_2010_Journal_of_Cultural.pdf |journal=Journal of Cultural Heritage |volume=11 |pages=196-204}}</ref> The recent extension of reflectography into the MWIR spectral region<ref>{{Cite journal |last=Daffara |first=C. |last2=Ambrosini |first2=D. |last3=Pezzati |first3=L. |last4=Paoletti |first4=D. |date=18 June 2012 |title=Thermal-quasi-reflectography: a new imaging tool in art conservation |url=https://opg.optica.org/oe/fulltext.cfm?uri=oe-20-13-14746 |journal=Optics Express |volume=20 |issue=13 |pages=14746-14753}}</ref><ref>{{Cite journal |last=Daffara |first=C. |last2=Parisotto |first2=S. |last3=Mariotti |first3=P. I. |last4=Ambrosini |first4=D. |date=18 November 2021 |title=Dual mode imaging in mid infrared with thermal signal reconstruction for innovative diagnostics of the “Monocromo” by Leonardo da Vinci |url=https://www.nature.com/articles/s41598-021-01837-8 |journal=Scientific Reports |volume=11 |pages=22482}}</ref> has proved capable of detecting subtle differences in surface materials. 

Finally, NIR reflectography can be performed with good results using smartphone cameras .<ref>{{Cite journal |last=Daffara |first=C. |last2=Ambrosini |first2=D. |date=14 August 2024 |title=Smartphone-based diagnostics with coherent and infrared imaging for cultural heritage |url=https://iopscience.iop.org/article/10.1088/2515-7647/ad6abc |journal=Journal of Physics: Photonics |volume=6 |pages=045006}}</ref>
<!--this is somewhat pointless without an accompanying I.R.:  Among many other changes in the [[Arnolfini Portrait]] of 1434 (left), the man's face was originally higher by about the height of his eye; the woman's was higher, and her eyes looked more to the front. Each of his feet was underdrawn in one position, painted in another, and then overpainted in a third. These alterations are seen in infrared reflectograms.<ref>National Gallery Catalogues: The Fifteenth Century Netherlandish Paintings by Lorne Campbell, 1998, {{ISBN|1-85709-171-X}}, {{OL|392219M}}, {{OCLC|40732051}}, {{LCCN|98066510}}, (also titled ''The Fifteenth Century Netherlandish Schools''){{Page needed|date=September 2010}}.</ref>-->

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.<ref>[http://colourlex.com/project/ir-reflectography/ Infrared reflectography in analysis of paintings] {{Webarchive|url=https://web.archive.org/web/20151222133807/http://colourlex.com/project/ir-reflectography/ |date=2015-12-22 }} at ColourLex.</ref> Notable examples are [[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 [[Dunhuang Caves]].<ref>{{Cite web |title=International Dunhuang Project An Introduction to digital infrared photography and its application within IDP |url=http://idp.bl.uk/pages/technical_resources.a4d |url-status=dead |archive-url=https://web.archive.org/web/20081202000830/http://idp.bl.uk/pages/technical_resources.a4d |archive-date=2008-12-02 |access-date=2011-11-08 |publisher=Idp.bl.uk}}</ref> Carbon black used in ink can show up extremely well.

=== Biological systems ===

{{further|Infrared sensing in snakes}}
[[File:wiki snake eats mouse.jpg|thumb|Thermographic image of a snake eating a mouse]]
<!-- [[File:wiki bat.jpg|thumb|Thermographic image of a [[fruit bat]].]] -->
The [[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.<ref>{{Cite journal |last=Jones |first=B.S. |last2=Lynn |first2=W.F. |last3=Stone |first3=M.O. |year=2001 |title=Thermal Modeling of Snake Infrared Reception: Evidence for Limited Detection Range |url=https://zenodo.org/record/1229918 |url-status=live |journal=Journal of Theoretical Biology |volume=209 |issue=2 |pages=201–211 |bibcode=2001JThBi.209..201J |doi=10.1006/jtbi.2000.2256 |pmid=11401462 |archive-url=https://web.archive.org/web/20200317210006/https://zenodo.org/record/1229918 |archive-date=2020-03-17 |access-date=2019-09-06}}</ref><ref>{{Cite journal |last=Gorbunov |first=V. |last2=Fuchigami |first2=N. |last3=Stone |first3=M. |last4=Grace |first4=M. |last5=Tsukruk |first5=V. V. |year=2002 |title=Biological Thermal Detection: Micromechanical and Microthermal Properties of Biological Infrared Receptors |journal=Biomacromolecules |volume=3 |issue=1 |pages=106–115 |doi=10.1021/bm015591f |pmid=11866562 |s2cid=21737304}}</ref>

Other organisms that have thermoreceptive organs are pythons (family [[Pythonidae]]), some boas (family [[Boidae]]), the [[Common Vampire Bat]] (''Desmodus rotundus''), a variety of [[jewel beetle]]s (''[[Melanophila acuminata]]''),<ref name="Evans">{{Cite journal |last=Evans |first=W.G. |year=1966 |title=Infrared receptors in ''Melanophila acuminata'' De Geer |journal=Nature |volume=202 |issue=4928 |page=211 |bibcode=1964Natur.202..211E |doi=10.1038/202211a0 |pmid=14156319 |s2cid=2553265 |doi-access=free}}</ref> darkly pigmented butterflies (''[[Pachliopta aristolochiae]]'' and ''[[Troides rhadamantus plateni]]''), and possibly blood-sucking bugs (''[[Triatoma infestans]]'').<ref name="Campbell-2002">{{Cite journal |last=Campbell |first=Angela L. |last2=Naik |first2=Rajesh R. |last3=Sowards |first3=Laura |last4=Stone |first4=Morley O. |year=2002 |title=Biological infrared imaging and sensing |url=https://zenodo.org/record/1260182 |url-status=live |journal=Micrometre |volume=33 |issue=2 |pages=211–225 |doi=10.1016/S0968-4328(01)00010-5 |pmid=11567889 |archive-url=https://web.archive.org/web/20200317150323/https://zenodo.org/record/1260182 |archive-date=2020-03-17 |access-date=2019-06-13}}</ref> By detecting the heat that their prey emits, [[crotaline]] and [[Booidea|boid snakes]] identify and capture their prey using their [[Infrared sensing in snakes|IR-sensitive pit organs]]. Comparably, IR-sensitive pits on the [[Common Vampire Bat]] (''Desmodus rotundus'') aid in the identification of blood-rich regions on its warm-blooded victim. The jewel beetle, ''[[Melanophila acuminata]]'', locates [[forest fires]] via infrared pit organs, where on recently burnt trees, they deposit their eggs. [[Thermoreceptors]] on the wings and antennae of butterflies with dark pigmentation, such ''[[Pachliopta aristolochiae]]'' and ''[[Troides rhadamantus plateni]]'', shield them from heat damage as they sunbathe in the sun. Additionally, it's hypothesised that thermoreceptors let bloodsucking bugs (''[[Triatoma infestans]]'') locate their [[warm-blooded]] victims by sensing their body heat.<ref name="Campbell-2002" />

Some fungi like ''[[Venturia inaequalis]]'' require near-infrared light for ejection.<ref>{{Cite journal |last=Brook |first=P. J. |date=26 April 1969 |title=Stimulation of Ascospore Release in Venturia inaequalis by Far Red Light |journal=Nature |language=En |volume=222 |issue=5191 |pages=390–392 |bibcode=1969Natur.222..390B |doi=10.1038/222390a0 |issn=0028-0836 |s2cid=4293713}}</ref>

Although near-infrared vision (780–1,000&nbsp;nm) has long been deemed impossible due to noise in visual pigments,<ref name="Meuthen et al.">{{Cite journal |last=Meuthen |first=Denis |last2=Rick |first2=Ingolf P. |last3=Thünken |first3=Timo |last4=Baldauf |first4=Sebastian A. |year=2012 |title=Visual prey detection by near-infrared cues in a fish |journal=Naturwissenschaften |volume=99 |issue=12 |pages=1063–6 |bibcode=2012NW.....99.1063M |doi=10.1007/s00114-012-0980-7 |pmid=23086394 |s2cid=4512517}}</ref> sensation of near-infrared light was reported in the common carp and in three cichlid species.<ref name="Meuthen et al." /><ref>{{Cite journal |last=Endo, M. |last2=Kobayashi R. |last3=Ariga, K. |last4=Yoshizaki, G. |last5=Takeuchi, T. |year=2002 |title=Postural control in tilapia under microgravity and the near infrared irradiated conditions |journal=Nippon Suisan Gakkaishi |volume=68 |issue=6 |pages=887–892 |doi=10.2331/suisan.68.887 |doi-access=free}}</ref><ref>{{Cite journal |last=Kobayashi R. |last2=Endo, M. |last3=Yoshizaki, G. |last4=Takeuchi, T. |year=2002 |title=Sensitivity of tilapia to infrared light measured using a rotating striped drum differs between two strains |journal=Nippon Suisan Gakkaishi |volume=68 |issue=5 |pages=646–651 |doi=10.2331/suisan.68.646 |doi-access=free}}</ref><ref>{{Cite journal |last=Matsumoto |first=Taro |last2=Kawamura |first2=Gunzo |year=2005 |title=The eyes of the common carp and Nile tilapia are sensitive to near-infrared |journal=Fisheries Science |volume=71 |issue=2 |pages=350–355 |bibcode=2005FisSc..71..350M |doi=10.1111/j.1444-2906.2005.00971.x |s2cid=24556470}}</ref><ref name="Shcherbakov et al.">{{Cite journal |last=Shcherbakov |first=Denis |last2=Knörzer |first2=Alexandra |last3=Hilbig |first3=Reinhard |last4=Haas |first4=Ulrich |last5=Blum |first5=Martin |year=2012 |title=Near-infrared orientation of Mozambique tilapia ''Oreochromis mossambicus'' |journal=Zoology |volume=115 |issue=4 |pages=233–238 |bibcode=2012Zool..115..233S |doi=10.1016/j.zool.2012.01.005 |pmid=22770589}}</ref> Fish use NIR to capture prey<ref name="Meuthen et al." /> and for phototactic swimming orientation.<ref name="Shcherbakov et al." /> NIR sensation in fish may be relevant under poor lighting conditions during twilight<ref name="Meuthen et al." /> and in turbid surface waters.<ref name="Shcherbakov et al." />

=== 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.<ref>{{Cite journal |last=Hargate |first=G |year=2006 |title=A randomised double-blind study comparing the effect of 1072-nm light against placebo for the treatment of herpes labialis |journal=Clinical and Experimental Dermatology |volume=31 |issue=5 |pages=638–41 |doi=10.1111/j.1365-2230.2006.02191.x |pmid=16780494 |s2cid=26977101}}</ref> Research projects include work on central nervous system healing effects via cytochrome c oxidase upregulation and other possible mechanisms.<ref>{{Cite journal |vauthors=Desmet KD, Paz DA, Corry JJ, Eells JT, Wong-Riley MT, Henry MM, Buchmann EV, Connelly MP, Dovi JV, Liang HL, Henshel DS, Yeager RL, Millsap DS, Lim J, Gould LJ, Das R, Jett M, Hodgson BD, Margolis D, Whelan HT |date=May 2006 |title=Clinical and experimental applications of NIR-LED photobiomodulation |url=https://epublications.marquette.edu/dentistry_fac/3 |url-status=live |journal=Photomedicine and Laser Surgery |volume=24 |issue=2 |pages=121–8 |doi=10.1089/pho.2006.24.121 |pmid=16706690 |s2cid=22442409 |archive-url=https://web.archive.org/web/20200316014302/https://epublications.marquette.edu/dentistry_fac/3/ |archive-date=2020-03-16 |access-date=2019-06-13}}</ref>

=== 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.<ref>{{Cite book |last=Rosso, Monona l |url=https://books.google.com/books?id=E7-9unTgJrwC&pg=PA33 |title=The Artist's Complete Health and Safety Guide |publisher=Allworth Press |year=2001 |isbn=978-1-58115-204-3 |pages=33–}}</ref>