Editing Night vision

{{short description|Ability to see in low light conditions}}
{{other uses|Night Vision (disambiguation)}}
[[Image:Nightvision.jpg|thumb|right|250px|Two [[United States|American]] soldiers pictured during the [[2003 invasion of Iraq]] seen through an [[image intensifier]].]]

'''Night vision''' is the ability to see in low-light conditions, either naturally with [[scotopic vision]] or through a [[night-vision device]]. Night vision requires both sufficient [[spectral range]] and sufficient [[luminous intensity|intensity range]]. Humans have poor night vision compared to many animals such as [[Cat vision|cats]], [[Dog_anatomy#Vision|dogs]], [[Fox|foxes]] and [[Rabbit|rabbits]], in part because the [[human eye]] lacks a [[tapetum lucidum]],<ref>{{cite journal |title= Histological study of choroidal melanocytes in animals with tapetum lucidum cellulosum (abstract) |doi= 10.1007/BF00935727 |volume=228 |issue= 2 |journal= Graefe's Archive for Clinical and Experimental Ophthalmology |pages= 161–168|year= 1990 |last1= Chijiiwa |first1= Taeko |last2= Ishibashi |first2= Tatsuro |last3= Inomata |first3= Hajime |pmid= 2338254 |s2cid= 11974069 }}</ref> tissue behind the retina that reflects light back through the retina thus increasing the light available to the photoreceptors.

==Types of ranges==
===Spectral range===
[[File:EM spectrum.svg|thumb|380px|The [[electromagnetic spectrum]], with the [[visible spectrum|visible portion]] highlighted]]

Night-useful spectral range techniques can sense radiation that is invisible to a human observer. Human vision is confined to a small portion of the [[electromagnetic spectrum]] called [[visible spectrum|visible light]]. Enhanced spectral range allows the viewer to take advantage of non-visible sources of electromagnetic radiation (such as near-[[infrared]] or [[ultraviolet]] radiation). Some animals such as the [[mantis shrimp]] and [[trout]] can see using much more of the infrared and/or ultraviolet spectrum than humans.<ref>{{cite journal |last=Milius |first=Susan |year=2012 |title=Mantis shrimp flub color vision test |journal=[[Science News]] |volume=182 |issue=6 |page=11 |jstor=23351000|doi=10.1002/scin.5591820609 }}</ref>

=== Intensity range ===
Sufficient intensity range is simply the ability to see with very small quantities of light.<ref>{{cite web|url=http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.html|title=The Human Eye and Single Photons}}</ref>

Many animals have better night vision than humans do, the result of one or more differences in the morphology and anatomy of their eyes. These include having a larger eyeball, a larger lens, a larger optical [[aperture]] (the pupils may expand to the physical limit of the eyelids), more rods than cones (or rods exclusively) in the [[retina]], and a [[tapetum lucidum]].

Enhanced intensity range is achieved via technological means through the use of an [[image intensifier]], gain multiplication [[Charge-coupled device|CCD]], or other very low-noise and high-sensitivity arrays of [[photodetector]]s.

==Biological night vision==
{{further|Adaptation (eye)#Accelerating dark adaptation|Scotopic vision}}

All [[photoreceptor cell]]s in the vertebrate eye contain molecules of [[Photoreceptor protein#Photoreceptors in animals|photoreceptor protein]] which is a combination of the protein [[photopsin]] in [[Cone cell|color vision cells]], [[rhodopsin]] in [[Rod cell|night vision cells]], and [[retinal]] (a small photoreceptor molecule). Retinal undergoes an irreversible change in shape when it absorbs light; this change causes an alteration in the shape of the protein which surrounds the retinal, and that alteration then induces the physiological process which results in vision.

The retinal must diffuse from the vision cell, out of the eye, and circulate via the blood to the liver where it is regenerated. In bright light conditions, most of the retinal is not in the photoreceptors, but is outside of the eye. It takes about 45 minutes of dark for ''all'' of the photoreceptor proteins to be recharged with active retinal, but most of the night vision [[Adaptation (eye)|adaptation]] occurs within the first five minutes in the dark.<ref name="Sensory">"Sensory Reception: Human Vision: Structure and function of the Human Eye" vol. 27, p. 179 Encyclopædia Britannica, 1987</ref> Adaptation results in maximum sensitivity to light. In dark conditions only the rod cells have enough sensitivity to respond and to trigger vision.
[[Image:Cone-response-en.svg|right|thumb|410px|Normalised [[absorption spectrum|absorption spectra]] of the three human photopsins and of human rhodopsin (dashed). Drawn after Bowmaker and Dartnall (1980).<ref>{{cite journal |last1=Bowmaker |first1=J K |last2=Dartnall |first2=H J |title=Visual pigments of rods and cones in a human retina. |journal=The Journal of Physiology |date=1 January 1980 |volume=298 |issue=1 |pages=501–511 |doi=10.1113/jphysiol.1980.sp013097 |pmid=7359434|pmc=1279132 }}</ref>]]

Rhodopsin in the human rods is insensitive to the longer red [[wavelengths]], so traditionally many people use red light to help preserve night vision. Red light only slowly depletes the rhodopsin stores in the rods, and instead is viewed by the red sensitive [[cone cell]]s.{{Citation needed|date=August 2019}}

Another theory posits that since stars typically emit light with shorter wavelengths, the light from stars will be in the blue-green color spectrum. Therefore, using red light to navigate would not desensitize the receptors used to detect star light.<ref>{{Cite journal |last1= Luria |first1= S.M. |last2= Kobus |first2= D.A. |publication-date= 26 April 1985 |date= April 1985 |title= Immediate Visibility after Red and White Adaptation |publisher= Naval Submarine Medical Research Laboratory |location= Submarine Base, Groton, CT |url= http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA156271&Location=U2&doc=GetTRDoc.pdf |journal=  |access-date= 25 March 2012 |archive-date= 1 December 2012 |archive-url= https://web.archive.org/web/20121201034224/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA156271&Location=U2&doc=GetTRDoc.pdf |url-status= dead }}</ref><ref>{{Cite journal| last1 = Luria| first1 = S. M.| last2 = Kobus| first2 = D. A.| publication-date = 3 July 1984| date=July 1984| title = THE RELATIVE EFFECTIVENESS OF RED AND WHITE LIGHT FOR SUBSEQUENT DARK-ADAPTATION| publisher = Naval Submarine Medical Research Laboratory| location = Submarine Base, Groton, CT |url= http://www.torpedo.nrl.navy.mil/tu/ps/pdf/pdf_loader?dsn=8969829}}{{dead link|date=April 2025|bot=medic}}{{cbignore|bot=medic}}</ref>

Many animals have a tissue layer called the ''[[tapetum lucidum]]'' in the back of the eye that reflects light back through the [[retina]], increasing the amount of light available for it to capture, but reducing the sharpness of the focus of the image. This is found in many [[nocturnal]] animals and some [[deep sea]] animals, and is the cause of eyeshine. Humans, and monkeys, lack a ''tapetum lucidum''.<ref>{{cite journal|url=https://makezine.com/projects/make-35/how-to-make-and-use-retroreflectors/ |title=How to Make and Use Retroreflectors |journal=Make |date=2013-10-03 |author=Forrest M. Mims III| access-date=2017-10-21}}</ref><ref>J. van de Kraats and D. van Norren: "Directional and nondirectional spectral reflection from the human fovea" J.Biomed. Optics, 13, 024010, 2008</ref>
[[File:Human eye in dim light.jpg|thumb|300x300px|The pupil of the eye dilates in the dark to enhance night vision. Shown here is a pupil of an adult naturally dilated to 9 mm in diameter in [[mesopic]] light levels. The average human eye is not able to dilate to this extent without the use of mydriatics.]]
Nocturnal mammals have rods with unique properties that make enhanced night vision possible. The nuclear pattern of their rods changes shortly after birth to become inverted. In contrast to conventional rods, inverted rods have [[heterochromatin]] in the center of their nuclei and [[euchromatin]] and other transcription factors along the border. In addition, the outer layer of cells in the retina (the [[outer nuclear layer]]) in nocturnal mammals is thick due to the millions of rods present to process the lower light intensities. The anatomy of this layer in nocturnal mammals is such that the rod nuclei, from individual cells, are physically stacked such that light will pass through eight to ten nuclei before reaching the photoreceptor portion of the cells. Rather than being scattered, the light is passed to each nucleus individually, by a strong lensing effect due to the nuclear inversion, passing out of the stack of nuclei, and into the stack of ten photorecepting [[rod cell|outer segments]]. The net effect of this anatomical change is to multiply the light sensitivity of the retina by a factor of eight to ten with no loss of focus.<ref>{{cite journal | author = Solovei, I. |author2=Kreysing, M. |author3=Lanctôt, C. |author4=Kösem, S. |author5=Peichl, L. |author6=Cremer, T. | date = April 16, 2009| title = Nuclear Architecture of Rod Photoreceptor Cells Adapts to Vision in Mammalian Evolution  | journal = Cell | volume = 137 | issue = 2 | pages = 945–953 | url = http://www.science-direct.com/science?_ob=ArticleURL&_udi=B6WSN-4W3325G-S&_user=10&_coverDate=04%2F17%2F2009&_rdoc=24&_fmt=high&_orig=browse&_srch=doc-info(%23toc%237051%232009%23998629997%231050051%23FLA%23display%23Volume)&_cdi=7051&_sort=d&_docanchor=&_ct=27&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=3dd47ebb589ebdd767f957eea220aa01  | doi = 10.1016/j.cell.2009.01.052 | pmid = 19379699|display-authors=etal| doi-access = free }}</ref>

[[Pupillary response|Pupillary dilation]] is a biological process that contributes a relatively minor amount to night vision. In humans, the irises can adjust the size of the pupil from 2 mm in bright light, to as large as 8 mm in dark conditions, but this varies by individual and age, with age causing the maximal pupil diameter to decrease. However, some humans are capable of dilating their pupils to over 9 mm in diameter in the dark, giving them better night vision capabilities.{{Citation needed|date=June 2024}}

==Night vision technologies==
[[File:Night vision.ogv|thumb|1974 [[US Army]] film about the development of military night vision technology]]

Night vision technologies can be broadly divided into three main categories: [[Image intensifier|image intensification]], active [[lighting|illumination]], and [[thermal imaging]]. Digital night vision is also emerging, which instead uses high sensitivity [[CMOS]] image sensors with a passthrough system.

===Image intensification===
{{Main|Image intensifier}}

This magnifies the amount of received photons from various natural sources such as [[starlight]] or moonlight. Examples of such technologies include night glasses and low light cameras. In the military context, Image Intensifiers are often called [[Low light level television|"Low Light TV"]] since the video signal is often transmitted to a display within a control center. These are usually integrated into a sensor containing both visible and IR detectors and the streams are used independently or in fused mode, depending on the mission at hand's requirements.<ref>{{Cite web |url=http://www.raytheon.com/media/sas/mts/ |title=Raytheon Multi-Spectral Targeting Systems (MTS) |access-date=2015-05-26 |archive-url=https://web.archive.org/web/20170903052528/http://www.raytheon.com/media/sas/mts/ |archive-date=2017-09-03 |url-status=dead }}</ref>

The image intensifier is a vacuum-tube based device (photomultiplier tube) that can generate an image from a very small number of photons (such as the light from stars in the sky) so that a dimly lit scene can be viewed in real-time by the naked eye via visual output, or stored as data for later analysis. While many believe the light is "amplified," it is not. When light strikes a charged [[photocathode]] plate, electrons are emitted through a vacuum tube and strike the microchannel plate. This causes the image screen to illuminate with a picture in the same pattern as the light that strikes the photocathode and on a wavelength the human eye can see. This is much like a [[CRT television]], but instead of color guns the photocathode does the emitting.

The image is said to become "intensified" because the output visible light is brighter than the incoming light, and this effect directly relates to the difference in passive and active [[night vision goggles]]. Currently, the most popular image intensifier is the drop-in [[ANVIS]] module, though many other models and sizes are available at the market. Recently, the US Navy announced intentions to procure a dual-color variant of the [[ANVIS]] for use in the cockpit of airborne platforms.<ref>{{Cite web |url=http://www.elbitsystems-us.com/sites/default/files/imported/airborne/hdts.pdf |title=Archived copy |access-date=2015-05-26 |archive-url=https://web.archive.org/web/20160304081443/http://www.elbitsystems-us.com/sites/default/files/imported/airborne/hdts.pdf |archive-date=2016-03-04 |url-status=dead }}</ref>

=== Digital night vision ===
Digital night vision relies on high sensitivity [[Back-illuminated sensor|back-illuminated]] [[CMOS]] image sensors, also sometimes called [[sCMOS]] (scientific CMOS). Their sensitivity can exceed the sensitivity of the human eye.<ref name="a897">{{cite web |title=Security Camera Image Sensor Technology STARVIS™/ STARVIS 2 |url=https://www.sony-semicon.com/en/technology/security/index.html |access-date=2025-02-02 |website=Sony Semiconductor Solutions Group}}</ref> These sensors can be head-mounted in night vision goggles and [[Telescopic sight|rifle scopes]], but are also used in [[security camera]] systems, [[astronomy]], and [[microscopy]].<ref name="x644">{{cite web |title=What is a Scientific CMOS Camera- Oxford Instruments |url=https://andor.oxinst.com/learning/view/article/scmos-technology-what-is-scmos |access-date=2025-02-02 |website=Oxford Instruments}}</ref> Infrared illumination can be used, but is not necessary for their functionality.

=== Active illumination ===
[[File:M3 Sniperscope.jpg|thumb|[[USMC]] M3 Sniperscope assembled on a [[M1 Carbine|M3 Carbine]]. Introduced during the [[Korean War]], it was an early active infrared night vision equipment powered by a large 12 volt battery that was carried in a rubberized canvas backpack.]]
[[File:M60 PattonMediumTank.jpg|thumb|An [[M60 tank]] with an infrared searchlight mounted on the cannon.]]

Active illumination couples imaging intensification technology with an active source of illumination in the [[near infrared]] (NIR) or shortwave infrared (SWIR) band. Examples of such technologies include low light cameras.

Active infrared night-vision combines infrared illumination of spectral range 700–1,000&nbsp;nm (just over the [[visible spectrum]] of the human eye) with sensors or [[charge-coupled device|CCD]] cameras sensitive to this light. The resulting scene, which is apparently dark to a human observer, appears as a monochrome image on a normal display device.<ref>{{cite web |title=YouTube mp3 indir |url=https://mp3video.org/ |website=mp3video.org}}</ref> Because active infrared night-vision systems can incorporate illuminators that produce high levels of infrared light, the resulting images are typically higher resolution than other night-vision technologies.<ref>{{cite web|url=http://www.irinfo.org/articles/03_01_2007_grossman.html |title=Thermal Infrared vs. Active Infrared: A New Technology Begins to be Commercialized |url-status=dead |archive-url=https://web.archive.org/web/20100117205639/http://www.irinfo.org/articles/03_01_2007_grossman.html |archive-date=January 17, 2010 }}</ref><ref>{{Cite web |url=http://www.extremecctv.com/products_video.php?vid=19 |title=Extreme CCTV Surveillance Systems |access-date=2008-01-24 |archive-url=https://web.archive.org/web/20080405225223/http://www.extremecctv.com/products_video.php?vid=19 |archive-date=2008-04-05 |url-status=dead }}</ref>  Active infrared night vision is now commonly found in commercial, residential and government security applications, where it enables effective night time imaging under low-light conditions. However, since active infrared light can be detected by night-vision goggles, there can be a risk of giving away position in tactical military operations.

Laser range gated imaging is another form of active night vision which utilizes a high powered pulsed light source for illumination and imaging. Range gating is a technique which controls the laser pulses in conjunction with the shutter speed of the camera's detectors.<ref>{{cite journal |author1=J. Bentell |author2=P. Nies |author3=J. Cloots |author4=J. Vermeiren |author5=B. Grietens |author6=O. David |author7=A. Shurkun |author8=R. Schneider | title = FLIP CHIPPED InGAaS PHOTODIODE ARRAYS FOR GATED IMAGING WITH EYE-SAFE LASERS  | url = http://www.couriertronics.com/docs/Xenics/Gated%20Imaging.pdf }}</ref> Gated imaging technology can be divided into ''single shot'', where the detector captures the image from a single light pulse, and ''multi-shot'', where the detector integrates the light pulses from multiple shots to form an image. One of the key advantages of this technique is the ability to perform [[target recognition]] rather than mere detection, as is the case with thermal imaging.

=== Thermal vision ===
{{see also|Thermographic camera|Forward-looking infrared}}
[[Thermal imaging]] detects the temperature difference between background and foreground objects. Some organisms are able to sense a crude thermal image by means of special organs that function as [[bolometer]]s. This allows thermal [[infrared sensing in snakes]], which functions by detecting thermal radiation.

[[Thermographic camera|Thermal imaging cameras]] are excellent tools for night vision. They detect [[thermal radiation]] and do not need a source of illumination. They produce an image in the darkest of nights and can see through light fog, rain, and smoke (to a certain extent). Thermal imaging cameras make small temperature differences visible. They are widely used to complement new or existing security networks, and for night vision on aircraft, where they are commonly referred to as "FLIR" (for "forward-looking infrared"). When coupled with additional cameras (for example, a visible spectrum camera or SWIR) multispectral sensors are possible, which take advantage of the benefits of each detection band's capabilities. Contrary to misconceptions portrayed in the media, thermal imagers cannot "see" through solid objects (walls, for example), nor can they see through glass or acrylic, as both these materials have their own thermal signature and are opaque to long wave infrared radiation.

== Night vision devices ==
{{Hatnote|See articles: [[Night-vision device]] and [[Thermal imaging camera]]}}

===History===
Before the introduction of image intensifiers, night glasses were the only method of night vision, and thus were widely utilized, especially at sea.<!---apparently used these in the late 19th century or even earlier---> Second World War era night glasses usually had a lens diameter of 56&nbsp;mm or more with magnification of seven or eight.  Major drawbacks of night glasses are their large size and weight.

===Current technology===
[[Image:Nachtsichtgeraet.jpg|thumb|right|Binocular night vision goggles on a flight helmet. The green color of the objective lenses is the reflection of the light interference filters, not a glow.]]
{{uncited section|date=December 2017}}<!--seems to have been uncited since 2012-->

A night vision device (NVD) is a device comprising an image intensifier tube in a rigid casing, commonly used by [[military forces]]. Lately, night vision technology has become more widely available for civilian use.  For example, [[enhanced vision system]]s (EVS) have become available for aircraft, to augment the situational awareness of pilots to prevent accidents.  These systems are included in the latest avionics packages from manufacturers such as [[Cirrus Aircraft|Cirrus]] and [[Cessna]]. The US Navy has begun procurement of a variant integrated into a helmet-mounted display, produced by Elbit Systems.

A specific type of NVD, the night vision goggle (NVG) is a night vision device with dual eyepieces.  The device can utilize either one intensifier tube with the same image sent to both eyes, or a separate image intensifier tube for each eye. Night vision goggles combined with magnification lenses constitutes night vision binoculars. Other types include monocular night vision devices with only one eyepiece which may be mounted to firearms as night sights. NVG and EVS technologies are becoming more popular with helicopter operations, to improve safety. The [[National Transportation Safety Board|NTSB]] is considering EVS as recommended equipment for safety features.

Night glasses are single or [[binocular vision|binocular]] with a large diameter objective. Large lenses can gather and concentrate light, thus intensifying light with purely optical means and enabling the user to see better in the dark than with the naked eye alone. Often night glasses also have a fairly large [[exit pupil]] of 7&nbsp;mm or more to let all gathered light into the user's eye. However, many people cannot take advantage of this because of the limited dilation of the human [[pupil]]. To overcome this, soldiers were sometimes issued [[atropine]] eye drops to dilate pupils.{{when|date=May 2012}}

Currently, the PVS-14 monocular is the most widely used and preferred night vision device across NATO forces. It is used by the United States army, and is known for its low cost and wide range of uses and modification ability. Some higher end devices including the PVS-31 binocular and GPNVG-18 quad-tube night vision are used by special forces groups, but are costly. Monoculars are generally preferred by developed forces.

Night vision systems can also be installed in vehicles. An [[automotive night vision]] system is used to improve a vehicle driver's perception and seeing distance in darkness or poor weather.  Such systems typically use infrared cameras, sometimes combined with active illumination techniques, to collect information that is then displayed to the driver. Such systems are currently offered as optional equipment on certain premium vehicles.

== See also ==
* [[Johnson's criteria]]
* [[Low light level television]]
* [[Night vision device]]
* [[Thermal imaging device]]
* [[Thermographic camera]]
* [[Averted vision]]

== References ==
{{Reflist|2}}

== External links ==
{{Commons category|Night vision}}
<!-- Please do not add links here that do not conform to the guidance at [[WP:EL]] else they will be removed without discussion.-->
* [https://web.archive.org/web/20110517135236/http://www.nvl.army.mil/ Night Vision & Electronic Sensors Directorate] - Fort Belvoir, [[Virginia]]
* [https://web.archive.org/web/20171126172906/http://www.cvel.clemson.edu/auto/systems/night-vision.html Automotive Night Vision Demonstration]

=== Patents ===
* {{US patent|D248860|US D248860 - Night vision Pocketscope}}
* {{US patent|4707595|US 4707595 - Invisible light beam projector and night vision system}}
* {{US patent|4991183|US 4991183 - Target illuminators and systems employing same}}
* {{US patent|6075644|US 6075644 - Panoramic night vision goggles}}
* {{US patent|7173237|US 7173237 - http://xenonics.sc48.biz/press/articles/article.php?article_id=67}}
* {{US patent|6158879|US 6158879 - Infra-red reflector and illumination system}}

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