Editing Infrared (section)

{{Short description|Form of electromagnetic radiation}}
{{Other uses}}
[[File:Ir girl.png|thumb|A [[false color|false-color]] image of two people taken in long-wavelength infrared (body-temperature thermal) radiation]]
'''Infrared''' ('''IR'''; sometimes called '''infrared light''') is [[electromagnetic radiation]] (EMR) with [[wavelength]]s longer than that of [[visible light]] but shorter than [[microwaves]]. The infrared [[spectral band]] begins with the waves that are just longer than those of [[red]] light (the longest waves in the [[visible spectrum]]), so IR is invisible to the human eye. IR is generally (according to ISO, CIE) understood to include wavelengths from around {{Convert|780|nm|THz|lk=on|abbr=on}} to {{Convert|1|mm|GHz|lk=on|abbr=on}}.<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><ref>{{Cite web |date=2024-09-18 |title=Definition of INFRARED |url=https://www.merriam-webster.com/dictionary/infrared |url-status=live |archive-url=https://web.archive.org/web/20240922080557/https://www.merriam-webster.com/dictionary/infrared |archive-date=2024-09-22 |access-date=2024-09-20 |website=www.merriam-webster.com |language=en}}</ref> IR is commonly divided between longer-wavelength thermal IR, emitted from terrestrial sources, and shorter-wavelength IR or near-IR, part of the [[solar spectrum]].<ref name="IPCC AR4-SYR">{{Cite web |title=IPCC AR4 SYR Appendix Glossary |url=https://ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_appendix.pdf |url-status=dead |archive-url=https://web.archive.org/web/20181117121314/http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_appendix.pdf |archive-date=2018-11-17 |access-date=2008-12-14}}</ref> Longer IR wavelengths (30–100&nbsp;μm) are sometimes included as part of the [[terahertz radiation]] band.<ref name="Rogalski-2019">{{Cite book |last=Rogalski |first=Antoni |title=Infrared and terahertz detectors |date=2019 |publisher=[[CRC Press]] | isbn=978-1-315-27133-0 |edition=3rd |location=Boca Raton, FL |page=929}}</ref>  Almost all [[black-body radiation]] from objects near [[room temperature]] is in the IR band. As a form of EMR, IR carries [[energy]] and [[momentum]], exerts [[radiation pressure]], and has properties corresponding to [[wave–particle duality|both]] those of a [[wave]] and of a [[subatomic particle|particle]], the [[photon]].<ref>{{Cite web |date=2024-09-18 |title=Infrared radiation {{!}} Definition, Wavelengths, & Facts {{!}} Britannica |url=https://www.britannica.com/science/infrared-radiation |access-date=2024-09-20 |website=www.britannica.com |language=en}}</ref>

It was long known that fires emit invisible [[heat]]; in 1681 the pioneering experimenter [[Edme Mariotte]] showed that glass, though transparent to sunlight, obstructed radiant heat.<ref>{{Cite web |last=Calel |first=Raphael |date=19 February 2014 |title=The Founding Fathers v. The Climate Change Skeptics |url=https://publicdomainreview.org/2014/02/19/the-founding-fathers-v-the-climate-change-skeptics/ |url-status=live |archive-url=https://web.archive.org/web/20191011112039/https://publicdomainreview.org/2014/02/19/the-founding-fathers-v-the-climate-change-skeptics/ |archive-date=11 October 2019 |access-date=16 September 2019 |website=The Public Domain Review}}</ref><ref>{{Cite web |last=Fleming |first=James R. |date=17 March 2008 |title=Climate Change and Anthropogenic Greenhouse Warming: A Selection of Key Articles, 1824–1995, with Interpretive Essays |url=http://nsdl.library.cornell.edu/websites/wiki/index.php/PALE_ClassicArticles/GlobalWarming.html |url-status=live |archive-url=https://web.archive.org/web/20190929065732/http://nsdl.library.cornell.edu/websites/wiki/index.php/PALE_ClassicArticles/GlobalWarming.html |archive-date=29 September 2019 |access-date=1 February 2022 |website=National Science Digital Library Project Archive PALE:ClassicArticles}} [http://nsdl.library.cornell.edu/websites/wiki/index.php/PALE_ClassicArticles/GlobalWarming/Article1.html Article 1: General remarks on the temperature of the earth and outer space] {{Webarchive|url=https://web.archive.org/web/20230608001830/http://nsdl.library.cornell.edu/websites/wiki/index.php/PALE_ClassicArticles/GlobalWarming/Article1.html |date=2023-06-08 }}.</ref> In 1800 the astronomer Sir [[William Herschel]] discovered that infrared radiation is a type of invisible radiation in the spectrum lower in energy than red light, by means of its effect on a [[thermometer]].<ref name="Michael Rowan">Michael Rowan-Robinson (2013). ''Night Vision: Exploring the Infrared Universe''. Cambridge University Press. p. 23. {{ISBN|1107024765}}.</ref> Slightly more than half of the energy from the [[Sun]] was eventually found, through Herschel's studies, to arrive on [[Earth]] in the form of infrared. The balance between absorbed and emitted infrared radiation has an important effect on Earth's [[climate]].

Infrared radiation is emitted or absorbed by [[molecule]]s when changing rotational-vibrational movements. It excites [[vibration]]al modes in a molecule through a change in the [[Molecular dipole moment|dipole moment]], making it a useful frequency range for study of these energy states for molecules of the proper symmetry. [[Infrared spectroscopy]] examines absorption and transmission of [[photon]]s in the infrared range.<ref>{{Cite web |last=Reusch |first=William |year=1999 |title=Infrared Spectroscopy |url=http://www.cem.msu.edu/~reusch/VirtualText/Spectrpy/InfraRed/infrared.htm |url-status=dead |archive-url=https://web.archive.org/web/20071027110406/http://www.cem.msu.edu/~reusch/VirtualText/Spectrpy/InfraRed/infrared.htm |archive-date=2007-10-27 |access-date=2006-10-27 |publisher=Michigan State University}}</ref>

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]] uses sensor-equipped [[telescope]]s to penetrate dusty regions of space such as [[molecular cloud]]s, to detect objects such as [[planet]]s, and to view highly [[red-shift]]ed objects from the early days of the [[universe]].<ref name="ir_astronomy">{{Cite web |title=IR Astronomy: Overview |url=http://www.ipac.caltech.edu/Outreach/Edu/importance.html |url-status=dead |archive-url=https://web.archive.org/web/20061208151300/http://www.ipac.caltech.edu/Outreach/Edu/importance.html |archive-date=2006-12-08 |access-date=2006-10-30 |publisher=NASA Infrared Astronomy and Processing Center}}</ref> Infrared thermal-imaging cameras are used to detect heat loss in insulated systems, to observe changing blood flow in the skin, to assist firefighting, and to detect the overheating of electrical components.<ref>{{Cite web |last=Chilton |first=Alexander |date=2013-10-07 |title=The Working Principle and Key Applications of Infrared Sensors |url=https://www.azosensors.com/article.aspx?ArticleID=339 |url-status=live |archive-url=https://web.archive.org/web/20200711215350/https://www.azosensors.com/article.aspx?ArticleID=339 |archive-date=2020-07-11 |access-date=2020-07-11 |website=AZoSensors |language=en}}</ref>  Military and civilian applications include [[target acquisition]], [[surveillance]], [[night vision]], [[homing (missile guidance)|homing]], and tracking. Humans at normal body temperature radiate chiefly at wavelengths around 10&nbsp;μm. Non-military uses include [[thermal efficiency]] analysis, environmental monitoring, industrial facility inspections, detection of [[grow-ops]], remote temperature sensing, short-range [[wireless communication]], [[spectroscopy]], and [[weather forecasting]].