Infrared

<h2 id="definition-and-relationship-to-the-electromagnetic-spectrum">Definition and relationship to the electromagnetic spectrum</h2>
There is no universally accepted definition of the range of infrared radiation. Typically, it is taken to extend from the nominal red edge of the visible spectrum at 780 nm to 1 mm. This range of wavelengths corresponds to a <a href="/facts/Frequency_spectrum/q3Rfs7b0">frequency</a> range of approximately 430 THz down to 300 GHz. Beyond infrared is the microwave portion of the <a href="/facts/Electromagnetic_spectrum/24LARvFY">electromagnetic spectrum</a>. Increasingly, terahertz radiation is counted as part of the microwave band, not infrared, moving the band edge of infrared to 0.1 mm (3 THz).

Position in the electromagnetic spectrum<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a><table><tbody><tr><th>Name</th><th><a href="/facts/Wavelength/kcJU0ymz">Wavelength</a></th><th><a href="/facts/Hertz/6Wshj5qm">Frequency (Hz)</a></th><th><a href="/facts/Electronvolt/YMT1fqX9">Photon energy (eV)</a></th></tr><tr><td><a href="/facts/Gamma_ray/5Drf913J">Gamma ray</a></td><td>less than 10 pm</td><td>more than 30 EHz</td><td>more than 124 keV</td></tr><tr><td><a href="/facts/X-ray/wseP79cN">X-ray</a></td><td>10 pm – 10 nm</td><td>30 PHz – 30 EHz</td><td>124 keV – 124 eV</td></tr><tr><td><a href="/facts/Ultraviolet/kncBUqn5">Ultraviolet</a></td><td>10 nm – 400 nm</td><td>750 THz – 30 PHz</td><td>124 eV – 3.3 eV</td></tr><tr><td><a href="/facts/Visible_light/jeofpMn4">Visible</a></td><td>400 nm – 700 nm</td><td>430 THz – 750 THz</td><td>3.3 eV – 1.7 eV</td></tr><tr><td>Infrared</td><td>700 nm – 1 mm</td><td>300 GHz – 430 THz</td><td>1.7 eV – 1.24 meV</td></tr><tr><td><a href="/facts/Microwave/HmVSN31Y">Microwave</a></td><td>1 mm – 1 meter</td><td>300 MHz – 300 GHz</td><td>1.24 meV – 1.24 μeV</td></tr><tr><td><a href="/facts/Radio_waves/XmB6WPpF">Radio</a></td><td>1 meter and more</td><td>300 MHz and below</td><td>1.24 μeV and below</td></tr></tbody></table>
<h2 id="nature">Nature</h2>
<a href="/facts/Sunlight/WPkJRC7s">Sunlight</a>, at an effective temperature of 5,780 <a href="/facts/Kelvin/E3trzC4C">K</a> (5,510 °C, 9,940 °F), is composed of near-thermal-spectrum radiation that is slightly more than half infrared. At <a href="/facts/Zenith/ISuRFp05">zenith</a>, sunlight provides an <a href="/facts/Irradiance/fgHwu7uh">irradiance</a> of just over 1 <a href="/facts/KW/VK8oqRrm">kW</a> per square meter at sea level. Of this energy, 527 W is infrared radiation, 445 W is visible light, and 32 W is <a href="/facts/Ultraviolet/kncBUqn5">ultraviolet</a> radiation.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> Nearly all the infrared radiation in sunlight is near infrared, shorter than 4 μm.
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. Black-body, or thermal, radiation is continuous: it radiates 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.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a>

<h2 id="regions">Regions</h2>
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 <a href="/facts/Wien%2527s_displacement_law/nrMVYWTF">Wien's displacement law</a>. 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.

<h3>Visible limit</h3>
Infrared radiation is generally considered to begin with wavelengths longer than visible by the human eye. 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 carry a large amount of energy. Even IR at wavelengths up to 1,050 nm from pulsed lasers can be seen by humans under certain conditions.<a class="footnote-ref" id="fnref:15" href="#fn:15">15</a><a class="footnote-ref" id="fnref:16" href="#fn:16">16</a><a class="footnote-ref" id="fnref:17" href="#fn:17">17</a>

<h3>Commonly used subdivision scheme</h3>
A commonly used subdivision scheme is:<a class="footnote-ref" id="fnref:18" href="#fn:18">18</a><a class="footnote-ref" id="fnref:19" href="#fn:19">19</a><a class="footnote-ref" id="fnref:20" href="#fn:20">20</a>

<table><tbody><tr><th>Division name</th><th>Abbreviation</th><th>Wavelength</th><th>Frequency</th><th>Photon energy</th><th>Temperature<a class="footnote-ref" id="fnref:21" href="#fn:21">21</a></th><th>Characteristics</th></tr><tr><th>Near-infrared</th><td>NIR, IR-A DIN</td><td>0.75–1.4 <a href="/facts/%25CE%259Cm/7eDFxD2L">μm</a></td><td>214–400 <a href="/facts/Terahertz_(unit)/6Wshj5qm">THz</a></td><td>886–1,653 <a href="/facts/MeV/YMT1fqX9">meV</a></td><td>3,864–2,070 <a href="/facts/Kelvin/E3trzC4C">K</a>(3,591–1,797 <a href="/facts/Celsius/okAEu1CA">°C</a>)</td><td>Goes up to the wavelength of the first <a href="/facts/Water_absorption/IbYMhjxC">water absorption</a> band, and commonly used in <a href="/facts/Fiber_optic/5ruuIFbj">fiber optic</a> telecommunication because of low attenuation losses in the SiO2 glass (<a href="/facts/Silica/A3WILp6J">silica</a>) medium. <a href="/facts/Image_intensifier/YoFhHNQb">Image intensifiers</a> are sensitive to this area of the spectrum; examples include <a href="/facts/Night_vision/tm6ToQgg">night vision</a> devices such as night vision goggles. <a href="/facts/Near-infrared_spectroscopy/gWCvHgYb">Near-infrared spectroscopy</a> is another common application.</td></tr><tr><th>Short-wavelength infrared</th><td>SWIR, IR-B DIN</td><td>1.4–3 μm</td><td>100–214 THz</td><td>413–886 meV</td><td>2,070–966 <a href="/facts/Kelvin/E3trzC4C">K</a>(1,797–693 <a href="/facts/Celsius/okAEu1CA">°C</a>)</td><td>Water absorption increases significantly at 1,450 nm. The 1,530 to 1,560 nm range is the dominant spectral region for long-distance telecommunications (see <a href="/facts/Fiber-optic_communication/dc6S0Hg5">transmission windows</a>).</td></tr><tr><th> Mid-wavelength infrared</th><td>MWIR, IR-C DIN; MidIR.<a class="footnote-ref" id="fnref:22" href="#fn:22">22</a> Also called intermediate infrared (IIR)</td><td>3–8 μm</td><td>37–100 THz</td><td>155–413 meV</td><td>966–362 <a href="/facts/Kelvin/E3trzC4C">K</a>(693–89 <a href="/facts/Celsius/okAEu1CA">°C</a>)</td><td>In guided missile technology the 3–5 μm portion of this band is the atmospheric window in which the seekers of passive IR 'heat seeking' missiles are designed to work, homing on to the <a href="/facts/Infrared_signature/od3S5Axr">infrared signature</a> of the target aircraft, typically the jet engine exhaust plume. This region is also known as thermal infrared.</td></tr><tr><th>Long-wavelength infrared</th><td>LWIR, IR-C DIN</td><td>8–15 μm</td><td>20–37 THz</td><td>83–155 meV</td><td>362–193 <a href="/facts/Kelvin/E3trzC4C">K</a>(89 – −80 <a href="/facts/Celsius/okAEu1CA">°C</a>)</td><td>The "thermal imaging" region, in which sensors can obtain a completely passive image of objects only slightly higher in temperature than room temperature – for example, the human body – based on thermal emissions only and requiring no illumination such as the sun or moon or an infrared illuminator. This region is also called the "thermal infrared".</td></tr><tr><th><a href="/facts/Far-infrared/rlup3DSX">Far-infrared</a></th><td>FIR</td><td>15–1,000 μm</td><td>0.3–20 THz</td><td>1.2–83 meV</td><td>193–3 <a href="/facts/Kelvin/E3trzC4C">K</a>(−80.15 – −270.15 <a href="/facts/Celsius/okAEu1CA">°C</a>)</td><td>(see also <a href="/facts/Far-infrared_laser/3qK53ayk">far-infrared laser</a> and <a href="/facts/Far-infrared/rlup3DSX">far-infrared</a>)</td></tr></tbody></table>

NIR and SWIR together is sometimes called "reflected infrared", whereas MWIR and LWIR is sometimes referred to as "thermal infrared".

<h3>CIE division scheme</h3>
The <a href="/facts/International_Commission_on_Illumination/46q6W1zk">International Commission on Illumination</a> (CIE) recommended the division of infrared radiation into the following three bands:<a class="footnote-ref" id="fnref:23" href="#fn:23">23</a><a class="footnote-ref" id="fnref:24" href="#fn:24">24</a>

<table><tbody><tr><th>Abbreviation</th><th>Wavelength</th><th>Frequency</th></tr><tr><td>IR-A</td><td>780–1400 nm</td><td>215–384 THz</td></tr><tr><td>IR-B</td><td>1400–3000 nm</td><td>100–215 THz</td></tr><tr><td>IR-C</td><td>3–1000 μm</td><td>0.3–100 THz</td></tr></tbody></table>
<h3>ISO 20473 scheme</h3>
<a href="/facts/ISO/IacYR7Yg">ISO</a> 20473 specifies the following scheme:<a class="footnote-ref" id="fnref:25" href="#fn:25">25</a>

<table><tbody><tr><th>Designation</th><th>Abbreviation</th><th>Wavelength</th></tr><tr><td>Near-infrared</td><td>NIR</td><td>0.78–3 μm</td></tr><tr><td>Mid-infrared</td><td>MIR</td><td>3–50 μm</td></tr><tr><td>Far-infrared</td><td>FIR</td><td>50–1,000 μm</td></tr></tbody></table>
<h3>Astronomy division scheme</h3>
Astronomers typically divide the infrared spectrum as follows:<a class="footnote-ref" id="fnref:26" href="#fn:26">26</a>

<table><tbody><tr><th>Designation</th><th>Abbreviation</th><th>Wavelength</th></tr><tr><td>Near-infrared</td><td>NIR</td><td>0.7–2.5 μm</td></tr><tr><td>Mid-infrared</td><td>MIR</td><td>3–25 μm</td></tr><tr><td>Far-infrared</td><td>FIR</td><td>above 25 μm</td></tr></tbody></table>
These divisions are not precise and can vary depending on the publication. The three regions are used for observation of different temperature ranges,<a class="footnote-ref" id="fnref:27" href="#fn:27">27</a> and hence different environments in space.
The most common photometric system used in astronomy allocates capital <a href="/facts/Jhk/7tUmLBGR">letters to different spectral regions</a> 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 <a href="/facts/Infrared_window/xKeM4VfJ">atmospheric windows</a> and appear, for instance, in the titles of many <a href="/facts/Academic_paper/WfPqsYr1">papers</a>.

<h3>Sensor response division scheme</h3>

A third scheme divides up the band based on the response of various detectors:<a class="footnote-ref" id="fnref:28" href="#fn:28">28</a>

<ul><li>Near-infrared: from 0.7 to 1.0 μm (from the approximate end of the response of the human eye to that of silicon).</li>
<li>Short-wave infrared: 1.0 to 3 μm (from the cut-off of silicon to that of the MWIR atmospheric window). <a href="/facts/InGaAs/DAHNSFPr">InGaAs</a> covers to about 1.8 μm; the less sensitive lead salts cover this region. Cryogenically cooled <a href="/facts/Mercury_cadmium_telluride/kzgN6aJn">MCT</a> detectors can cover the region of 1.0–2.5 μm.</li>
<li>Mid-wave infrared: 3 to 5 μm (defined by the atmospheric window and covered by <a href="/facts/Indium_antimonide/76EPwVLC">indium antimonide</a>, InSb and <a href="/facts/Mercury_cadmium_telluride/kzgN6aJn">mercury cadmium telluride</a>, HgCdTe, and partially by <a href="/facts/Lead_selenide/66h19tQ2">lead selenide</a>, PbSe).</li>
<li>Long-wave infrared: 8 to 12, or 7 to 14 μm (this is the atmospheric window covered by HgCdTe and <a href="/facts/Microbolometer/390o08xp">microbolometers</a>).</li>
<li>Very-long wave infrared (VLWIR) (12 to about 30 μm, covered by doped silicon).</li></ul>
Near-infrared is the region closest in wavelength to the radiation detectable by the human eye. mid- and far-infrared are progressively further from the visible spectrum. Other definitions follow different physical mechanisms (emission peaks, vs. bands, water absorption) and the newest follow technical reasons (the common <a href="/facts/Silicon/cgWx0hdr">silicon</a> detectors are sensitive to about 1,050 nm, while <a href="/facts/InGaAs/DAHNSFPr">InGaAs</a>'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. Particularly intense near-IR light (e.g., from <a href="/facts/Laser/jk6PTvvT">lasers</a>, LEDs or bright daylight with the visible light filtered out) 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 <a href="/facts/Wood_effect/yj1Py5T8">Wood effect</a> that consists of IR-glowing foliage.<a class="footnote-ref" id="fnref:29" href="#fn:29">29</a>

<h3>Telecommunication bands</h3>
In <a href="/facts/Optical_communications/gshoNBto">optical communications</a>, 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:<a class="footnote-ref" id="fnref:30" href="#fn:30">30</a>

<table><tbody><tr><th>Band</th><th>Descriptor</th><th>Wavelength range</th></tr><tr><td>O band</td><td>Original</td><td>1,260–1,360 nm</td></tr><tr><td>E band</td><td>Extended</td><td>1,360–1,460 nm</td></tr><tr><td>S band</td><td>Short wavelength</td><td>1,460–1,530 nm</td></tr><tr><td><a href="/facts/C_band_(infrared)/6F0EEcDI">C band</a></td><td>Conventional</td><td>1,530–1,565 nm</td></tr><tr><td>L band</td><td>Long wavelength</td><td>1,565–1,625 nm</td></tr><tr><td>U band</td><td>Ultralong wavelength</td><td>1,625–1,675 nm</td></tr></tbody></table>
The C-band is the dominant band for long-distance <a href="/facts/Telecommunications_network/NFCX0STS">telecommunications networks</a>. The S and L bands are based on less well established technology, and are not as widely deployed.

<h2 id="heat">Heat</h2>
Main article: <a href="/facts/Thermal_radiation/1PD9jtCv">Thermal radiation</a>

Infrared radiation is popularly known as "heat radiation",<a class="footnote-ref" id="fnref:31" href="#fn:31">31</a> but light and electromagnetic waves of any frequency will heat surfaces that absorb them. Infrared light from the Sun accounts for 49%<a class="footnote-ref" id="fnref:32" href="#fn:32">32</a> 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-emitting lasers can char paper and incandescently hot objects emit visible radiation. Objects at room <a href="/facts/Temperature/QyGe4gmj">temperature</a> will <a href="/facts/Spontaneous_emission/kWWfqQ2V">emit</a> <a href="/facts/Thermal_radiation/1PD9jtCv">radiation</a> 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 <a href="/facts/Black_body/f0fHghDy">black body</a> and <a href="/facts/Wien%2527s_displacement_law/nrMVYWTF">Wien's displacement law</a>).<a class="footnote-ref" id="fnref:33" href="#fn:33">33</a>
<a href="/facts/Heat/FjDGssCs">Heat</a> is energy in transit that flows due to a temperature difference. Unlike heat transmitted by <a href="/facts/Thermal_conduction/5vRktgcS">thermal conduction</a> or <a href="/facts/Thermal_convection/3r5MHqdg">thermal convection</a>, thermal radiation can propagate through a <a href="/facts/Vacuum/BTk3goyV">vacuum</a>. 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 <a href="/facts/Solar_corona/W4WNqV9u">solar corona</a>). 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 <a href="/facts/Emissivity/LUxfMRRI">emissivity</a> 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 ideal of a <a href="/facts/Black_body/f0fHghDy">black body</a>. 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.

<h2 id="applications">Applications</h2>
<h3>Night vision</h3>
Main article: <a href="/facts/Night_vision/tm6ToQgg">Night vision</a>
 Infrared is used in night vision equipment when there is insufficient visible light to see.<a class="footnote-ref" id="fnref:34" href="#fn:34">34</a> <a href="/facts/Night_vision_devices/jJ58YGa0">Night vision devices</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.<a class="footnote-ref" id="fnref:35" href="#fn:35">35</a> 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.<a class="footnote-ref" id="fnref:36" href="#fn:36">36</a><a class="footnote-ref" id="fnref:37" href="#fn:37">37</a>
The use of infrared light and night vision devices should not be confused with <a href="/facts/Thermal_imaging/DWxF0CsD">thermal imaging</a>, which creates images based on differences in surface temperature by detecting infrared radiation (<a href="/facts/Heat/FjDGssCs">heat</a>) that emanates from objects and their surrounding environment.<a class="footnote-ref" id="fnref:38" href="#fn:38">38</a><a class="footnote-ref" id="fnref:39" href="#fn:39">39</a>

<h3>Thermography</h3>
Main article: <a href="/facts/Thermography/DWxF0CsD">Thermography</a>
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 <a href="/facts/Pyrometry/Pmwlb9b9">pyrometry</a>. 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.
<a href="/facts/Thermographic_cameras/dplJK39u">Thermographic cameras</a> detect radiation in the infrared range of the electromagnetic spectrum (roughly 9,000–14,000 nm 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).

<h3>Hyperspectral imaging</h3>
Main article: <a href="/facts/Hyperspectral_imaging/3NsxsAeL">Hyperspectral imaging</a>

A hyperspectral image is a "picture" containing continuous <a href="/facts/Infrared_spectroscopy/u1Hzx617">spectrum</a> 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 <a href="/facts/Thermographic_camera/dplJK39u">thermographic camera</a>, 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 <a href="/facts/UAV/qt87T19t">UAV</a> applications.<a class="footnote-ref" id="fnref:40" href="#fn:40">40</a>

<h3>Other imaging</h3>

In <a href="/facts/Infrared_photography/VHHECAPR">infrared photography</a>, <a href="/facts/Infrared_filter/QgfRYdBy">infrared filters</a> are used to capture the near-infrared spectrum. <a href="/facts/Digital_camera/LSGTserm">Digital cameras</a> often use infrared <a href="/facts/Filter_(optics)/WdCmGqaq">blockers</a>. Cheaper digital cameras and <a href="/facts/Camera_phones/EzCfpkdl">camera phones</a> 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 '<a href="/facts/T-ray/729QecPK">T-ray</a>' imaging, which is imaging using <a href="/facts/Far-infrared/rlup3DSX">far-infrared</a> or <a href="/facts/Terahertz_radiation/729QecPK">terahertz radiation</a>. 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 <a href="/facts/Terahertz_time-domain_spectroscopy/yLXAY1lW">terahertz time-domain spectroscopy</a>.

<h3>Tracking</h3>

Main article: <a href="/facts/Infrared_homing/shTBbEmn">Infrared homing</a>
Infrared tracking, also known as infrared homing, refers to a <a href="/facts/Passive_homing/NSna0Dtk">passive missile guidance system</a>, which uses the <a href="/facts/Light_emission/FRTheSWG">emission</a> 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.<a class="footnote-ref" id="fnref:41" href="#fn:41">41</a>

<h3>Heating</h3>
Main article: <a href="/facts/Infrared_heating/JjbAmRqT">Infrared heating</a>

Infrared radiation can be used as a deliberate heating source. For example, it is used in <a href="/facts/Infrared_sauna/DfJfumDl">infrared saunas</a> 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).<a class="footnote-ref" id="fnref:42" href="#fn:42">42</a>
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.

<h3>Cooling</h3>
Main article: <a href="/facts/Passive_daytime_radiative_cooling/ljL5fKxN">Passive daytime radiative cooling</a>
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's <a href="/facts/Infrared_window/xKeM4VfJ">infrared window</a>. This is how <a href="/facts/Passive_daytime_radiative_cooling/ljL5fKxN">passive daytime radiative cooling</a> (PDRC) surfaces are able to achieve sub-ambient cooling temperatures under direct solar intensity, enhancing terrestrial <a href="/facts/Heat_flow/1IV3WbFL">heat flow</a> to outer space with zero <a href="/facts/Efficient_energy_use/8K8vBAVk">energy consumption</a> or <a href="/facts/Pollution/JRagxumQ">pollution</a>.<a class="footnote-ref" id="fnref:43" href="#fn:43">43</a><a class="footnote-ref" id="fnref:44" href="#fn:44">44</a> PDRC surfaces maximize shortwave <a href="/facts/Solar_reflectance/TJDRdKEB">solar reflectance</a> to lessen heat gain while maintaining strong longwave infrared (LWIR) <a href="/facts/Thermal_radiation/1PD9jtCv">thermal radiation</a> <a href="/facts/Heat_transfer/1IV3WbFL">heat transfer</a>.<a class="footnote-ref" id="fnref:45" href="#fn:45">45</a><a class="footnote-ref" id="fnref:46" href="#fn:46">46</a> When imagined on a worldwide scale, this cooling method has been proposed as a way to slow and even reverse <a href="/facts/Global_warming/rEN4BDE7">global warming</a>, with some estimates proposing a global surface area coverage of 1-2% to balance global heat fluxes.<a class="footnote-ref" id="fnref:47" href="#fn:47">47</a><a class="footnote-ref" id="fnref:48" href="#fn:48">48</a>

<h3>Communications</h3>
Further information: <a href="/facts/Consumer_IR/Wv7S6qBP">Consumer IR</a>
IR data transmission is also employed in short-range communication among computer peripherals and <a href="/facts/Personal_digital_assistant/fLTT1Uqy">personal digital assistants</a>. These devices usually conform to standards published by <a href="/facts/IrDA/qf8bwPDD">IrDA</a>, the Infrared Data Association. Remote controls and IrDA devices use infrared <a href="/facts/Light-emitting_diode/gE8x4MDb">light-emitting diodes</a> (LEDs) to emit infrared radiation that may be concentrated by a <a href="/facts/Lens/ejlH6n5c">lens</a> into a beam that the user aims at the detector. The beam is <a href="/facts/On%25E2%2580%2593off_keying/8HkJV9am">modulated</a>, 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 <a href="/facts/Silicon/cgWx0hdr">silicon</a> <a href="/facts/Photodiode/152Rpk06">photodiodes</a>, which the receiver uses to convert the detected radiation to an <a href="/facts/Electric_current/Dc1xdnUX">electric current</a>. That electrical signal is passed through a <a href="/facts/High-pass_filter/W2G9Pbyw">high-pass filter</a> 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 <a href="/facts/Remote_control/A9zmkgIV">remote controls</a> to command appliances.
Infrared remote control protocols like <a href="/facts/RC-5/78o9YPNh">RC-5</a>, SIRC, are used to communicate with infrared.
<a href="/facts/Free-space_optical_communication/V3lyvTxk">Free-space optical communication</a> using infrared <a href="/facts/Laser/jk6PTvvT">lasers</a> 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."<a class="footnote-ref" id="fnref:49" href="#fn:49">49</a>
Infrared lasers are used to provide the light for <a href="/facts/Optical_fiber/5ruuIFbj">optical fiber</a> communications systems. Wavelengths around 1,330 nm (least <a href="/facts/Dispersion_(optics)/cUdHnYXz">dispersion</a>) or 1,550 nm (best transmission) are the best choices for standard <a href="/facts/Silica/A3WILp6J">silica</a> fibers.
IR data transmission of audio versions of printed signs is being researched as an aid for visually impaired people through the <a href="/facts/Remote_infrared_audible_signage/W2AdaMoY">Remote infrared audible signage</a> project.
Transmitting IR data from one device to another is sometimes referred to as <a href="/facts/Beaming/oYA5XSjj">beaming</a>.
IR is sometimes used for assistive audio as an alternative to an <a href="/facts/Audio_induction_loop/oK2smcCh">audio induction loop</a>.

<h3>Spectroscopy</h3>
<a href="/facts/Infrared_spectroscopy/u1Hzx617">Infrared vibrational spectroscopy</a> (see also <a href="/facts/Near-infrared_spectroscopy/gWCvHgYb">near-infrared spectroscopy</a>) 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 <a href="/facts/Dipole/G1vRqruD">dipole</a> in the molecule then it will absorb a <a href="/facts/Photon/mFNhAEzA">photon</a> 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 <a href="/facts/Organic_compound/gqCNaN45">organic compounds</a> 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 <a href="/facts/Wavenumber/cLaLAeW5">wavenumber</a>. It is the frequency divided by the speed of light in vacuum.

<h3>Thin film metrology</h3>
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 <a href="/facts/Forouhi%25E2%2580%2593Bloomer_model/myoPDSmF">Forouhi–Bloomer dispersion equations</a>. 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.

<h3>Meteorology</h3>

<a href="/facts/Weather_satellite/yl7QCK8n">Weather satellites</a> 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 <a href="/facts/Cyclone/T8IEU0aP">cyclones</a> or <a href="/facts/Cumulonimbus_cloud/DPWNqTDE">cumulonimbus clouds</a>, are often displayed as red or black, lower warmer clouds such as <a href="/facts/Stratus_cloud/xGz9XQNU">stratus</a> or <a href="/facts/Stratocumulus/xMpHbmbj">stratocumulus</a> 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 <a href="/facts/Fog/mrIdyIc7">fog</a> 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 μm) and the near-infrared channel (1.58–1.64 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 <a href="/facts/El_Ni%25C3%25B1o/HsqetArr">El Niño</a> 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.

<h3>Climatology</h3>

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 <a href="/facts/Global_warming/rEN4BDE7">global warming</a>, together with <a href="/facts/Solar_radiation/SI26I7aD">solar radiation</a>.
A <a href="/facts/Pyrgeometer/XSIYIrWa">pyrgeometer</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.

<h3>Astronomy</h3>
Main articles: <a href="/facts/Infrared_astronomy/WEmAadyf">Infrared astronomy</a> and <a href="/facts/Far-infrared_astronomy/jwjIFDYB">far-infrared astronomy</a>

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 <a href="/facts/Optical_astronomy/bbfzMHAn">optical astronomy</a>. 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 <a href="/facts/Helium/yRul93TG">helium</a>.
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 <a href="/facts/Infrared_window/xKeM4VfJ">atmospheric windows</a>. 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 <a href="/facts/Molecular_cloud/5jEwCJxs">molecular clouds</a> 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 <a href="/facts/Protostar/fhQYMSBA">protostars</a> 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 <a href="/facts/Planet/rbPjE6Bx">planets</a> 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 <a href="/facts/Active_galaxies/qT1owvXz">active galaxies</a>, which are often cloaked in gas and dust. Distant galaxies with a high <a href="/facts/Redshift/Qfl4VjDF">redshift</a> will have the peak portion of their spectrum shifted toward longer wavelengths, so they are more readily observed in the infrared.<a class="footnote-ref" id="fnref:50" href="#fn:50">50</a>

<h3>Cleaning</h3>
<a href="/facts/Infrared_cleaning/XuDYD9Uy">Infrared cleaning</a> is a technique used by some <a href="/facts/Motion_picture_film_scanner/Nj8a424c">motion picture film scanners</a>, <a href="/facts/Film_scanner/nxrhEvwj">film scanners</a> and <a href="/facts/Flatbed_scanner/7DEJFTwx">flatbed scanners</a> to reduce or remove the effect of dust and scratches upon the finished <a href="/facts/Image_scanning/7DEJFTwx">scan</a>. 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 <a href="/facts/Inpainting/5fHD96N8">inpainting</a>.<a class="footnote-ref" id="fnref:51" href="#fn:51">51</a>

<h3>Art conservation and analysis</h3>

Infrared reflectography<a class="footnote-ref" id="fnref:52" href="#fn:52">52</a> can be applied to paintings to reveal underlying layers in a non-destructive manner, in particular the artist's <a href="/facts/Underdrawing/P4rAFBBW">underdrawing</a> 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 <a href="/facts/Pentimenti/9D4Waz3s">pentimenti</a> when made by the original artist). This is very useful information in deciding whether a painting is the <a href="/facts/Prime_version/M7UlhNz3">prime version</a> 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.<a class="footnote-ref" id="fnref:53" href="#fn:53">53</a> Reflectography often reveals the artist's use of <a href="/facts/Carbon_black/xmPdCHFp">carbon black</a>, 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. <a class="footnote-ref" id="fnref:54" href="#fn:54">54</a> The recent extension of reflectography into the MWIR spectral region<a class="footnote-ref" id="fnref:55" href="#fn:55">55</a><a class="footnote-ref" id="fnref:56" href="#fn:56">56</a> has proved capable of detecting subtle differences in surface materials. 
Finally, NIR reflectography can be performed with good results using smartphone cameras .<a class="footnote-ref" id="fnref:57" href="#fn:57">57</a>
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.<a class="footnote-ref" id="fnref:58" href="#fn:58">58</a> Notable examples are <a href="/facts/Picasso/qM7WAcBA">Picasso</a>'s <a href="/facts/Woman_Ironing/jJBKkeXB">Woman Ironing</a> and <a href="/facts/Blue_Room_(Picasso)/KfMH8n2e">Blue Room</a>, 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 <a href="/facts/Dead_Sea_Scrolls/vlbHRrJm">Dead Sea Scrolls</a>, the Roman works in the <a href="/facts/Villa_of_the_Papyri/hrSoH9Sk">Villa of the Papyri</a>, and the Silk Road texts found in the <a href="/facts/Dunhuang_Caves/I6LPaYxv">Dunhuang Caves</a>.<a class="footnote-ref" id="fnref:59" href="#fn:59">59</a> Carbon black used in ink can show up extremely well.

<h3>Biological systems</h3>
Further information: <a href="/facts/Infrared_sensing_in_snakes/pR5rT4RB">Infrared sensing in snakes</a>

The <a href="/facts/Pit_viper/wMmmcb4z">pit viper</a> has a pair of infrared sensory pits on its head. There is uncertainty regarding the exact thermal sensitivity of this biological infrared detection system.<a class="footnote-ref" id="fnref:60" href="#fn:60">60</a><a class="footnote-ref" id="fnref:61" href="#fn:61">61</a>
Other organisms that have thermoreceptive organs are pythons (family <a href="/facts/Pythonidae/U3T63eYB">Pythonidae</a>), some boas (family <a href="/facts/Boidae/0Y5FKhM2">Boidae</a>), the <a href="/facts/Common_Vampire_Bat/pg6a2QAv">Common Vampire Bat</a> (Desmodus rotundus), a variety of <a href="/facts/Jewel_beetle/RW7ACINx">jewel beetles</a> (<a href="/facts/Melanophila_acuminata/78b9grJt">Melanophila acuminata</a>),<a class="footnote-ref" id="fnref:62" href="#fn:62">62</a> darkly pigmented butterflies (<a href="/facts/Pachliopta_aristolochiae/CACAcBKH">Pachliopta aristolochiae</a> and Troides rhadamantus plateni), and possibly blood-sucking bugs (<a href="/facts/Triatoma_infestans/fSXHrWwL">Triatoma infestans</a>).<a class="footnote-ref" id="fnref:63" href="#fn:63">63</a> By detecting the heat that their prey emits, <a href="/facts/Crotaline/wMmmcb4z">crotaline</a> and <a href="/facts/Booidea/qUcua9dT">boid snakes</a> identify and capture their prey using their <a href="/facts/Infrared_sensing_in_snakes/pR5rT4RB">IR-sensitive pit organs</a>. Comparably, IR-sensitive pits on the <a href="/facts/Common_Vampire_Bat/pg6a2QAv">Common Vampire Bat</a> (Desmodus rotundus) aid in the identification of blood-rich regions on its warm-blooded victim. The jewel beetle, <a href="/facts/Melanophila_acuminata/78b9grJt">Melanophila acuminata</a>, locates <a href="/facts/Forest_fires/LU3797A0">forest fires</a> via infrared pit organs, where on recently burnt trees, they deposit their eggs. <a href="/facts/Thermoreceptors/sH49VAy0">Thermoreceptors</a> on the wings and antennae of butterflies with dark pigmentation, such <a href="/facts/Pachliopta_aristolochiae/CACAcBKH">Pachliopta aristolochiae</a> and Troides rhadamantus plateni, shield them from heat damage as they sunbathe in the sun. Additionally, it's hypothesised that thermoreceptors let bloodsucking bugs (<a href="/facts/Triatoma_infestans/fSXHrWwL">Triatoma infestans</a>) locate their <a href="/facts/Warm-blooded/vw2TsPIP">warm-blooded</a> victims by sensing their body heat.<a class="footnote-ref" id="fnref:64" href="#fn:64">64</a>
Some fungi like <a href="/facts/Venturia_inaequalis/dlt0FYAK">Venturia inaequalis</a> require near-infrared light for ejection.<a class="footnote-ref" id="fnref:65" href="#fn:65">65</a>
Although near-infrared vision (780–1,000 nm) has long been deemed impossible due to noise in visual pigments,<a class="footnote-ref" id="fnref:66" href="#fn:66">66</a> sensation of near-infrared light was reported in the common carp and in three cichlid species.<a class="footnote-ref" id="fnref:67" href="#fn:67">67</a><a class="footnote-ref" id="fnref:68" href="#fn:68">68</a><a class="footnote-ref" id="fnref:69" href="#fn:69">69</a><a class="footnote-ref" id="fnref:70" href="#fn:70">70</a><a class="footnote-ref" id="fnref:71" href="#fn:71">71</a> Fish use NIR to capture prey<a class="footnote-ref" id="fnref:72" href="#fn:72">72</a> and for phototactic swimming orientation.<a class="footnote-ref" id="fnref:73" href="#fn:73">73</a> NIR sensation in fish may be relevant under poor lighting conditions during twilight<a class="footnote-ref" id="fnref:74" href="#fn:74">74</a> and in turbid surface waters.<a class="footnote-ref" id="fnref:75" href="#fn:75">75</a>

<h3>Photobiomodulation</h3>
Near-infrared light, or <a href="/facts/Photobiomodulation/MkPhrePV">photobiomodulation</a>, is used for treatment of chemotherapy-induced oral ulceration as well as wound healing. There is some work relating to anti-herpes virus treatment.<a class="footnote-ref" id="fnref:76" href="#fn:76">76</a> Research projects include work on central nervous system healing effects via cytochrome c oxidase upregulation and other possible mechanisms.<a class="footnote-ref" id="fnref:77" href="#fn:77">77</a>

<h3>Health hazards</h3>
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.<a class="footnote-ref" id="fnref:78" href="#fn:78">78</a>

<h2 id="scientific-history">Scientific history</h2>
The discovery of infrared radiation is ascribed to <a href="/facts/William_Herschel/SsruaBvq">William Herschel</a>, the <a href="/facts/Astronomer/ronF8j4a">astronomer</a>, in the early 19th century. Herschel published his results in 1800 before the <a href="/facts/Royal_Society_of_London/KI5yXCuV">Royal Society of London</a>. Herschel used a <a href="/facts/Triangular_prism_(optics)/87fCcXBo">prism</a> to <a href="/facts/Refract/S8kvSKzM">refract</a> light from the <a href="/facts/Sun/CadPCVHh">sun</a> and detected the infrared, beyond the <a href="/facts/Red/gLnFAVx4">red</a> part of the spectrum, through an increase in the temperature recorded on a <a href="/facts/Thermometer/almVTBxI">thermometer</a>. He was surprised at the result and called them "Calorific Rays".<a class="footnote-ref" id="fnref:79" href="#fn:79">79</a><a class="footnote-ref" id="fnref:80" href="#fn:80">80</a> The term "infrared" did not appear until late 19th century.<a class="footnote-ref" id="fnref:81" href="#fn:81">81</a> The Latin prefix infra- means below, as it is light below red on the spectrum.<a class="footnote-ref" id="fnref:82" href="#fn:82">82</a> An <a href="/facts/Pictet%2527s_experiment/c3lWbHvc">earlier experiment in 1790</a> by <a href="/facts/Marc-Auguste_Pictet/W6k34HT3">Marc-Auguste Pictet</a> demonstrated the reflection and focusing of radiant heat via mirrors in the absence of visible light.<a class="footnote-ref" id="fnref:83" href="#fn:83">83</a>
Other important dates include:<a class="footnote-ref" id="fnref:84" href="#fn:84">84</a>

<ul><li>1830: <a href="/facts/Leopoldo_Nobili/pXyYvl0b">Leopoldo Nobili</a> made the first <a href="/facts/Thermopile/cTuF62oI">thermopile</a> IR detector.<a class="footnote-ref" id="fnref:85" href="#fn:85">85</a></li>
<li>1840: <a href="/facts/John_Herschel/Hcg9pFEp">John Herschel</a> produces the first thermal image, called a <a href="/facts/Thermogram/DWxF0CsD">thermogram</a>.<a class="footnote-ref" id="fnref:86" href="#fn:86">86</a></li>
<li>1860: <a href="/facts/Gustav_Kirchhoff/Ygfzlywy">Gustav Kirchhoff</a> formulated the <a href="/facts/Kirchhoff%2527s_law_of_thermal_radiation/JCLTqWeF">blackbody theorem</a> 
 
 
 
 E
 =
 J
 (
 T
 ,
 n
 )
 
 
 {\displaystyle E=J(T,n)}
 
.<a class="footnote-ref" id="fnref:87" href="#fn:87">87</a></li>
<li>1873: <a href="/facts/Willoughby_Smith/Iah1seIX">Willoughby Smith</a> discovered the photoconductivity of <a href="/facts/Selenium/k975NApC">selenium</a>.<a class="footnote-ref" id="fnref:88" href="#fn:88">88</a></li>
<li>1878: <a href="/facts/Samuel_Pierpont_Langley/jHj588ru">Samuel Pierpont Langley</a> invents the first <a href="/facts/Bolometer/5YlzCoe8">bolometer</a>, a device which is able to measure small temperature fluctuations, and thus the power of far infrared sources.<a class="footnote-ref" id="fnref:89" href="#fn:89">89</a></li>
<li>1879: <a href="/facts/Stefan%25E2%2580%2593Boltzmann_law/vA4tbwKC">Stefan–Boltzmann law</a> formulated empirically that the power radiated by a blackbody is proportional to T4.<a class="footnote-ref" id="fnref:90" href="#fn:90">90</a></li>
<li>1880s and 1890s: <a href="/facts/Lord_Rayleigh/HcJyYdk5">Lord Rayleigh</a> and <a href="/facts/Wilhelm_Wien/Fm4W3S11">Wilhelm Wien</a> solved part of the blackbody equation, but both solutions diverged in parts of the electromagnetic spectrum. This problem was called the "<a href="/facts/Ultraviolet_catastrophe/rRM4PTQU">ultraviolet catastrophe</a> and infrared catastrophe".<a class="footnote-ref" id="fnref:91" href="#fn:91">91</a></li>
<li>1892: Willem Henri Julius published infrared spectra of 20 organic compounds measured with a bolometer in units of angular displacement.<a class="footnote-ref" id="fnref:92" href="#fn:92">92</a></li>
<li>1901: <a href="/facts/Max_Planck/KKk0698y">Max Planck</a> published the <a href="/facts/Planck%2527s_law/7Umkdb9m">blackbody equation</a> and theorem. He solved the problem by quantizing the allowable energy transitions.<a class="footnote-ref" id="fnref:93" href="#fn:93">93</a></li>
<li>1905: <a href="/facts/Albert_Einstein/CNTet8qu">Albert Einstein</a> developed the theory of the <a href="/facts/Photoelectric_effect/gIDcdm5U">photoelectric effect</a>.<a class="footnote-ref" id="fnref:94" href="#fn:94">94</a></li>
<li>1905–1908: <a href="/facts/William_Coblentz/fAEmd8Ls">William Coblentz</a> published infrared spectra in units of wavelength (micrometers) for several chemical compounds in Investigations of Infra-Red Spectra.<a class="footnote-ref" id="fnref:95" href="#fn:95">95</a><a class="footnote-ref" id="fnref:96" href="#fn:96">96</a><a class="footnote-ref" id="fnref:97" href="#fn:97">97</a></li>
<li>1917: <a href="/facts/Theodore_Case/kS2QRsjF">Theodore Case</a> developed the <a href="/facts/Thallous_sulfide/HLlyzQX3">thallous sulfide</a> detector, which helped produce the first <a href="/facts/Infrared_search_and_track/YLjLE9hf">infrared search and track</a> device able to detect aircraft at a range of one mile (1.6 km).</li>
<li>1935: Lead salts – early missile guidance in <a href="/facts/World_War_II/2efV5L1U">World War II</a>.</li>
<li>1938: Yeou Ta predicted that the pyroelectric effect could be used to detect infrared radiation.<a class="footnote-ref" id="fnref:98" href="#fn:98">98</a></li>
<li>1945: The <a href="/facts/Zielger%25C3%25A4t_1229/gKh0ICGb">Zielgerät 1229</a> "Vampir" infrared weapon system was introduced as the first portable infrared device for military applications.</li>
<li>1952: <a href="/facts/Heinrich_Welker/XYxWKpwv">Heinrich Welker</a> grew synthetic <a href="/facts/InSb/76EPwVLC">InSb</a> crystals.</li>
<li>1950s and 1960s: Nomenclature and radiometric units defined by Fred Nicodemenus, G. J. Zissis and R. Clark; <a href="/facts/Robert_Clark_Jones/1oBkor2E">Robert Clark Jones</a> defined D*.</li>
<li>1958: W. D. Lawson (<a href="/facts/Royal_Radar_Establishment/jsUq834G">Royal Radar Establishment</a> in Malvern) discovered IR detection properties of <a href="/facts/Mercury_cadmium_telluride/kzgN6aJn">Mercury cadmium telluride</a> (HgCdTe).<a class="footnote-ref" id="fnref:99" href="#fn:99">99</a></li>
<li>1958: <a href="/facts/AIM-4_Falcon/cKcljVcd">Falcon</a> and <a href="/facts/AIM-9_Sidewinder/LPm7nQTT">Sidewinder</a> missiles were developed using infrared technology.</li>
<li>1960s: Paul Kruse and his colleagues at <a href="/facts/Honeywell/qjkujlwJ">Honeywell</a> Research Center demonstrate the use of HgCdTe as an effective <a href="/facts/Chemical_compound/37FXqqtv">compound</a> for infrared detection.<a class="footnote-ref" id="fnref:100" href="#fn:100">100</a></li>
<li>1962: J. Cooper demonstrated pyroelectric detection.<a class="footnote-ref" id="fnref:101" href="#fn:101">101</a></li>
<li>1964: W. G. Evans discovered infrared thermoreceptors in a pyrophile beetle.<a class="footnote-ref" id="fnref:102" href="#fn:102">102</a></li>
<li>1965: First IR handbook; first commercial imagers (Barnes, Agema (now part of <a href="/facts/FLIR_Systems/lv3rEzMS">FLIR Systems</a> Inc.)); Richard Hudson's landmark text; F4 TRAM FLIR by <a href="/facts/Hughes_Aircraft_Company/NURPFI17">Hughes</a>; phenomenology pioneered by Fred Simmons and A. T. Stair; U.S. Army's night vision lab formed (now <a href="/facts/Night_Vision_and_Electronic_Sensors_Directorate/GKTITvMw">Night Vision and Electronic Sensors Directorate</a> (NVESD)), and Rachets develops detection, recognition and identification modeling there.</li>
<li>1970: <a href="/facts/Willard_Boyle/Dryt56Lb">Willard Boyle</a> and <a href="/facts/George_E._Smith/754bKDcs">George E. Smith</a> proposed CCD at <a href="/facts/Bell_Labs/fKP5Gk0H">Bell Labs</a> for <a href="/facts/Picture_phone/Ya9TMFQD">picture phone</a>.</li>
<li>1973: Common module program started by NVESD.<a class="footnote-ref" id="fnref:103" href="#fn:103">103</a></li>
<li>1978: Infrared imaging astronomy came of age, observatories planned, <a href="/facts/NASA_Infrared_Telescope_Facility/J6moYhjV">IRTF</a> on Mauna Kea opened; 32 × 32 and 64 × 64 arrays produced using InSb, HgCdTe and other materials.</li>
<li>2013: On 14 February, researchers developed a <a href="/facts/Neural_implant/eaHAKydz">neural implant</a> that gives <a href="/facts/Rat/5rn6uEKM">rats</a> the ability to sense infrared light, which for the first time provides <a href="/facts/Living_creatures/j8JkL09u">living creatures</a> with new abilities, instead of simply replacing or augmenting existing abilities.<a class="footnote-ref" id="fnref:104" href="#fn:104">104</a></li></ul>
<h2 id="see-also">See also</h2>

<ul><li><a href="/facts/Black-body_radiation/K4YKPKXL">Black-body radiation</a></li>
<li><a href="/facts/Infrared_non-destructive_testing_of_materials/lMU7XkmK">Infrared non-destructive testing of materials</a></li>
<li><a href="/facts/Solar_cell/3L814UCC">Infrared solar cells</a></li>
<li><a href="/facts/Infrared_thermometer/X2UDBl6Q">Infrared thermometer</a></li>
<li><a href="/facts/People_counter/r93Gs4a5">People counter</a></li>
<li><a href="/facts/Index_of_infrared_articles/qjLDDLxm">Index of infrared articles</a></li></ul>
<h2 id="notes">Notes</h2>

<h2 id="external-links">External links</h2>

<ul><li><a href="http://www.omega.com/literature/transactions/volume1/historical1.html">Infrared: A Historical Perspective</a> <a href="https://web.archive.org/web/20070807034953/http://www.omega.com/literature/transactions/volume1/historical1.html">Archived</a> 2007-08-07 at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a> (Omega Engineering)</li>
<li><a href="http://www.irda.org/">Infrared Data Association</a> <a href="https://web.archive.org/web/20080522132313/http://www.irda.org/">Archived</a> 2008-05-22 at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a>, a standards organization for infrared data interconnection</li>
<li><a href="http://yengal-marumugam.blogspot.com/2011/06/sirc-part-i-basics.html">SIRC Protocol</a> <a href="https://web.archive.org/web/20111013110621/http://yengal-marumugam.blogspot.com/2011/06/sirc-part-i-basics.html">Archived</a> 2011-10-13 at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a></li>
<li><a href="http://www.ocinside.de/html/modding/usb_ir_receiver/usb_ir_receiver.html">How to build a USB infrared receiver to control PC's remotely</a> <a href="https://web.archive.org/web/20110719165527/http://www.ocinside.de/html/modding/usb_ir_receiver/usb_ir_receiver.html">Archived</a> 2011-07-19 at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a></li>
<li><a href="https://web.archive.org/web/20060114051647/http://imagers.gsfc.nasa.gov/ems/infrared.html">Infrared Waves</a>: detailed explanation of infrared light. (NASA)</li>
<li><a href="https://archive.org/details/philtrans08733349">Herschel's original paper from 1800 announcing the discovery of infrared light</a></li>
<li><a href="http://www.thethermograpiclibrary.org/index.php/Cat%C3%A9gorie:Library">The thermographic's library</a> <a href="https://web.archive.org/web/20130611022731/http://www.thethermograpiclibrary.org/index.php/Cat%C3%A9gorie:Library">Archived</a> 2013-06-11 at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a>, collection of thermogram</li>
<li><a href="http://colourlex.com/project/ir-reflectography/">Infrared reflectography in analysis of paintings</a> <a href="https://web.archive.org/web/20151222133807/http://colourlex.com/project/ir-reflectography/">Archived</a> 2015-12-22 at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a> at ColourLex</li>
<li>Molly Faries, <a href="http://www.nap.edu/read/11413/chapter/8">Techniques and Applications – Analytical Capabilities of Infrared Reflectography: An Art Historian s Perspective</a> <a href="https://web.archive.org/web/20151222152730/http://www.nap.edu/read/11413/chapter/8">Archived</a> 2015-12-22 at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a>, in Scientific Examination of Art: Modern Techniques in Conservation and Analysis, Sackler NAS Colloquium, 2005</li></ul>

<h2 id="references">References</h2>

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<li id="fn:81">In 1867, French physicist Edmond Becquerel coined the term infra-rouge (infra-red):
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The word infra-rouge was translated into English as "infrared" in 1874, in a translation of an article by Vignaud Dupuy de Saint-Florent (1830–1907), an engineer in the French army, who attained the rank of lieutenant colonel and who pursued photography as a pastime.
de Saint-Florent (10 April 1874). "Photography in natural colours". The Photographic News. 18: 175–176. Archived from the original on 5 February 2021. Retrieved 15 April 2018. From p. 176: "As to the infra-red rays, they may be absorbed by means of a weak solution of sulphate of copper, ..."
See also:
Rosenberg, Gary (2012). "Letter to the Editors: Infrared dating". American Scientist. 100 (5): 355. Archived from the original on 2018-04-15. Retrieved 2018-04-15.
 <a href="/wiki/Edmond_Becquerel" target="_blank">/wiki/Edmond_Becquerel</a> <a href="#fnref:81" class="footnote-back-ref">↩</a></li>
<li id="fn:82">Harper, Douglas. "infrared". Online Etymology Dictionary. Retrieved 2025-04-07. <a href="https://www.etymonline.com/?term=infrared" target="_blank">https://www.etymonline.com/?term=infrared</a> <a href="#fnref:82" class="footnote-back-ref">↩</a></li>
<li id="fn:83">Chang, Hasok (2007). Inventing temperature: measurement and scientific progress. Oxford studies in philosophy of science (1. issued as paperback ed.). Oxford: Oxford University Press. pp. 166–167. ISBN 978-0-19-533738-9. <a href="978-0-19-533738-9" target="_blank">978-0-19-533738-9</a> <a href="#fnref:83" class="footnote-back-ref">↩</a></li>
<li id="fn:84">Miller, Principles of Infrared Technology (Van Nostrand Reinhold, 1992), and Miller and Friedman, Photonic Rules of Thumb, 2004. ISBN 978-0-442-01210-6[page needed] <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:84" class="footnote-back-ref">↩</a></li>
<li id="fn:85">See:
Nobili, Leopoldo (1830). "Description d'un thermo-multiplicateur ou thermoscope électrique" [Description of a thermo-multiplier or electric thermoscope]. Bibliothèque Universelle (in French). 44: 225–234. Archived from the original on 2021-02-24. Retrieved 2018-04-12.
Nobili; Melloni (1831). "Recherches sur plusieurs phénomènes calorifiques entreprises au moyen du thermo-multiplicateur" [Investigations of several heat phenomena undertaken via a thermo-multiplier]. Annales de Chimie et de Physique. 2nd series (in French). 48: 198–218. Archived from the original on 2021-02-05. Retrieved 2018-04-12.
Vollmer, Michael; Möllmann, Klaus-Peter (2010). Infrared Thermal Imaging: Fundamentals, Research and Applications (2nd ed.). Berlin, Germany: Wiley-VCH. pp. 1–67. ISBN 978-3-527-69329-0. Archived from the original on 2024-09-22. Retrieved 2018-04-12.
 <a href="978-3-527-69329-0" target="_blank">978-3-527-69329-0</a> <a href="#fnref:85" class="footnote-back-ref">↩</a></li>
<li id="fn:86">Herschel, John F. W. (1840). "On chemical action of rays of solar spectrum on preparation of silver and other substances both metallic and nonmetallic and on some photographic processes". Philosophical Transactions of the Royal Society of London. 130: 1–59. Bibcode:1840RSPT..130....1H. doi:10.1098/rstl.1840.0002. S2CID 98119765. Archived from the original on 2021-02-05. Retrieved 2018-04-09. The term "thermograph" is coined on p. 51: " ... I have discovered a process by which the calorific rays in the solar spectrum are made to leave their impress on a surface properly prepared for the purpose, so as to form what may be called a thermograph of the spectrum, ... ". <a href="https://babel.hathitrust.org/cgi/pt?id=pst.000054592933;view=1up;seq=47" target="_blank">https://babel.hathitrust.org/cgi/pt?id=pst.000054592933;view=1up;seq=47</a> <a href="#fnref:86" class="footnote-back-ref">↩</a></li>
<li id="fn:87">See:
Kirchhoff (1859). "Ueber den Zusammenhang von Emission und Absorption von Licht und Warme" [On the relation between emission and absorption of light and heat]. Monatsberichte der Königlich-Preussischen Akademie der Wissenschaften zu Berlin (Monthly Reports of the Royal Prussian Academy of Philosophy in Berlin) (in German): 783–787. Archived from the original on 2020-09-25. Retrieved 2018-04-10.
Kirchhoff, G. (1860). "Ueber das Verhältnis zwischen dem Emissionsvermögen und dem Absorptionsvermögen der Körper für Wärme und Licht" [On the relation between bodies' emission capacity and absorption capacity for heat and light]. Annalen der Physik und Chemie (in German). 109 (2): 275–301. Bibcode:1860AnP...185..275K. doi:10.1002/andp.18601850205. Retrieved 2018-04-10.
English translation: Kirchhoff, G. (1860). "On the relation between the radiating and absorbing powers of different bodies for light and heat". Philosophical Magazine. 4th series. 20: 1–21. Archived from the original on 2021-02-05. Retrieved 2018-04-11.
 <a href="https://babel.hathitrust.org/cgi/pt?id=mdp.39015049219333;view=1up;seq=811" target="_blank">https://babel.hathitrust.org/cgi/pt?id=mdp.39015049219333;view=1up;seq=811</a> <a href="#fnref:87" class="footnote-back-ref">↩</a></li>
<li id="fn:88">See:
Smith, Willoughby (1873). "The action of light on selenium". Journal of the Society of Telegraph Engineers. 2 (4): 31–33. doi:10.1049/jste-1.1873.0023. Archived from the original on 2024-10-03. Retrieved 2018-04-09.
Smith, Willoughby (20 February 1873). "Effect of light on selenium during the passage of an electric current". Nature. 7 (173): 303. Bibcode:1873Natur...7R.303.. doi:10.1038/007303e0. Archived from the original on 3 January 2021. Retrieved 9 April 2018.
 <a href="https://zenodo.org/record/1429782" target="_blank">https://zenodo.org/record/1429782</a> <a href="#fnref:88" class="footnote-back-ref">↩</a></li>
<li id="fn:89">See:
Langley, S. P. (1880). "The bolometer". Proceedings of the American Metrological Society. 2: 184–190. Archived from the original on 2021-02-05. Retrieved 2018-04-09.
Langley, S. P. (1881). "The bolometer and radiant energy". Proceedings of the American Academy of Arts and Sciences. 16: 342–358. doi:10.2307/25138616. JSTOR 25138616. Archived from the original on 2021-02-05. Retrieved 2018-04-09.
 <a href="https://babel.hathitrust.org/cgi/pt?id=nyp.33433090766035;view=1up;seq=282" target="_blank">https://babel.hathitrust.org/cgi/pt?id=nyp.33433090766035;view=1up;seq=282</a> <a href="#fnref:89" class="footnote-back-ref">↩</a></li>
<li id="fn:90">Stefan, J. (1879). "Über die Beziehung zwischen der Wärmestrahlung und der Temperatur" [On the relation between heat radiation and temperature]. Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften [Wien]: Mathematisch-naturwissenschaftlichen Classe (Proceedings of the Imperial Academy of Philosophy [in Vienna]: Mathematical-scientific Class) (in German). 79: 391–428. Archived from the original on 2019-04-02. Retrieved 2018-04-11. <a href="https://babel.hathitrust.org/cgi/pt?id=hvd.32044093294874;view=1up;seq=419" target="_blank">https://babel.hathitrust.org/cgi/pt?id=hvd.32044093294874;view=1up;seq=419</a> <a href="#fnref:90" class="footnote-back-ref">↩</a></li>
<li id="fn:91">See:
Wien, Willy (1896). "Ueber die Energieverteilung im Emissionsspektrum eines schwarzen Körpers" [On the energy distribution in the emission spectrum of a black body]. Annalen der Physik und Chemie. 3rd series (in German). 58: 662–669. Archived from the original on 2021-02-24. Retrieved 2018-04-10.
English translation: Wien, Willy (1897). "On the division of energy in the emission-spectrum of a black body". Philosophical Magazine. 5th series. 43 (262): 214–220. doi:10.1080/14786449708620983. Archived from the original on 2021-02-05. Retrieved 2018-04-10.
 <a href="https://babel.hathitrust.org/cgi/pt?id=wu.89048352850;view=1up;seq=676" target="_blank">https://babel.hathitrust.org/cgi/pt?id=wu.89048352850;view=1up;seq=676</a> <a href="#fnref:91" class="footnote-back-ref">↩</a></li>
<li id="fn:92">Julius, Willem Henri (1892). Bolometrisch onderzoek van absorptiespectra (in Dutch). J. Müller. Archived from the original on 2024-09-22. Retrieved 2020-10-18. <a href="https://books.google.com/books?id=K1AVAAAAIAAJ&q=Bolometrisch+Ondersoek+van+Absorptiespectra&pg=PA44" target="_blank">https://books.google.com/books?id=K1AVAAAAIAAJ&q=Bolometrisch+Ondersoek+van+Absorptiespectra&pg=PA44</a> <a href="#fnref:92" class="footnote-back-ref">↩</a></li>
<li id="fn:93">See:
Planck, M. (1900). "Ueber eine Verbesserung der Wien'schen Spectralgleichung" [On an improvement of Wien's spectral equation]. Verhandlungen der Deutschen Physikalischen Gesellschaft (in German). 2: 202–204. Archived from the original on 2024-09-22. Retrieved 2018-04-10.
Planck, M. (1900). "Zur Theorie des Gesetzes der Energieverteilung im Normalspectrum" [On the theory of the law of energy distribution in the normal spectrum]. Verhandlungen der Deutschen Physikalischen Gesellschaft (in German). 2: 237–245. Archived from the original on 2021-02-25. Retrieved 2018-04-10.
Planck, Max (1901). "Ueber das Gesetz der Energieverteilung im Normalspectrum" [On the law of energy distribution in the normal spectrum]. Annalen der Physik. 4th series (in German). 4 (3): 553–563. Bibcode:1901AnP...309..553P. doi:10.1002/andp.19013090310. Archived from the original on 2021-02-06. Retrieved 2018-04-10.
 <a href="https://babel.hathitrust.org/cgi/pt?id=coo.31924056107224;view=1up;seq=516" target="_blank">https://babel.hathitrust.org/cgi/pt?id=coo.31924056107224;view=1up;seq=516</a> <a href="#fnref:93" class="footnote-back-ref">↩</a></li>
<li id="fn:94">See:
Einstein, A. (1905). "Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt" [On heuristic viewpoint concerning the production and transformation of light]. Annalen der Physik. 4th series (in German). 17 (6): 132–148. Bibcode:1905AnP...322..132E. doi:10.1002/andp.19053220607.
English translation: Arons, A. B.; Peppard, M. B. (1965). "Einstein's proposal of the photon concept—a translation of the Annalen der Physik paper of 1905". American Journal of Physics. 33 (5): 367–374. Bibcode:1965AmJPh..33..367A. doi:10.1119/1.1971542. S2CID 27091754. Available at Wayback Machine.
 <a href="https://archive.org/stream/annalenderphysi108unkngoog#page/n150/mode/2up" target="_blank">https://archive.org/stream/annalenderphysi108unkngoog#page/n150/mode/2up</a> <a href="#fnref:94" class="footnote-back-ref">↩</a></li>
<li id="fn:95">Coblentz, William Weber (1905). Investigations of Infra-red Spectra: Part I, II. Carnegie institution of Washington. Archived from the original on 2024-09-22. Retrieved 2020-10-18. <a href="https://books.google.com/books?id=qVUoHbyKbDsC&q=coblentz,+william+weber&pg=PP7" target="_blank">https://books.google.com/books?id=qVUoHbyKbDsC&q=coblentz,+william+weber&pg=PP7</a> <a href="#fnref:95" class="footnote-back-ref">↩</a></li>
<li id="fn:96">Coblentz, William Weber (1905). Investigations of Infra-red Spectra: Part III, IV. University of Michigan. Washington, D.C., Carnegie institution of Washington. <a href="https://archive.org/details/investigationsi01coblgoog" target="_blank">https://archive.org/details/investigationsi01coblgoog</a> <a href="#fnref:96" class="footnote-back-ref">↩</a></li>
<li id="fn:97">Coblentz, William Weber (August 1905). Investigations of Infra-red Spectra: Part V, VI, VII. University of California Libraries. Washington, D.C. : Carnegie Institution of Washington. <a href="https://archive.org/details/investigationsof03coblrich" target="_blank">https://archive.org/details/investigationsof03coblrich</a> <a href="#fnref:97" class="footnote-back-ref">↩</a></li>
<li id="fn:98">Waste Energy Harvesting: Mechanical and Thermal Energies. Springer Science & Business Media. 2014. p. 406. ISBN 978-3-642-54634-1. Archived from the original on 2024-09-22. Retrieved 2020-01-07. <a href="978-3-642-54634-1" target="_blank">978-3-642-54634-1</a> <a href="#fnref:98" class="footnote-back-ref">↩</a></li>
<li id="fn:99">Marion B. Reine (2015). "Interview with Paul W. Kruse on the Early History of HgCdTe (1980)" (PDF). Journal of Electronic Materials. 44 (9). doi:10.1007/s11664-015-3737-1. S2CID 95341284. Archived (PDF) from the original on 2020-07-30. Retrieved 2020-01-07. <a href="https://link.springer.com/content/pdf/10.1007/s11664-015-3737-1.pdf" target="_blank">https://link.springer.com/content/pdf/10.1007/s11664-015-3737-1.pdf</a> <a href="#fnref:99" class="footnote-back-ref">↩</a></li>
<li id="fn:100">Marion B. Reine (2015). "Interview with Paul W. Kruse on the Early History of HgCdTe (1980)" (PDF). Journal of Electronic Materials. 44 (9). doi:10.1007/s11664-015-3737-1. S2CID 95341284. Archived (PDF) from the original on 2020-07-30. Retrieved 2020-01-07. <a href="https://link.springer.com/content/pdf/10.1007/s11664-015-3737-1.pdf" target="_blank">https://link.springer.com/content/pdf/10.1007/s11664-015-3737-1.pdf</a> <a href="#fnref:100" class="footnote-back-ref">↩</a></li>
<li id="fn:101">J Cooper (1962). "A fast-response pyroelectric thermal detector". Journal of Scientific Instruments. 39 (9): 467–472. Bibcode:1962JScI...39..467C. doi:10.1088/0950-7671/39/9/308. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:101" class="footnote-back-ref">↩</a></li>
<li id="fn:102">Evans, W.G. (1966). "Infrared receptors in Melanophila acuminata De Geer". Nature. 202 (4928): 211. Bibcode:1964Natur.202..211E. doi:10.1038/202211a0. PMID 14156319. S2CID 2553265. <a href="https://doi.org/10.1038%2F202211a0" target="_blank">https://doi.org/10.1038%2F202211a0</a> <a href="#fnref:102" class="footnote-back-ref">↩</a></li>
<li id="fn:103">"History of Army Night Vision". C5ISR Center. Archived from the original on March 16, 2020. Retrieved 2020-01-07. <a href="https://web.archive.org/web/20200316225350/https://c5isr.ccdc.army.mil/inside_c5isr_center/nvesd/history/" target="_blank">https://web.archive.org/web/20200316225350/https://c5isr.ccdc.army.mil/inside_c5isr_center/nvesd/history/</a> <a href="#fnref:103" class="footnote-back-ref">↩</a></li>
<li id="fn:104">"Implant gives rats sixth sense for infrared light". Wired UK. 14 February 2013. Archived from the original on 17 February 2013. Retrieved 14 February 2013. <a href="https://www.wired.co.uk/news/archive/2013-02/14/implant-gives-rats-sixth-sense-for-infrared-light" target="_blank">https://www.wired.co.uk/news/archive/2013-02/14/implant-gives-rats-sixth-sense-for-infrared-light</a> <a href="#fnref:104" class="footnote-back-ref">↩</a></li>
</ol>

Infrared open-in-new

Infrared