A night-vision device (NVD), also known as a night optical/observation device (NOD) or night-vision goggle (NVG), is an optoelectronic device that allows visualization of images in low levels of light, improving the user's night vision.
The device enhances ambient visible light and converts near-infrared light into visible light which can then be seen by humans; this is known as I2 (image intensification). By comparison, viewing of infrared thermal radiation is referred to as thermal imaging and operates in a different section of the infrared spectrum.
A night vision device usually consists of an image intensifier tube, a protective housing, and an optional mounting system. Many NVDs also include a protective sacrificial lens, mounted over the front/objective lens to prevent damage by environmental hazards,[1] while some incorporate telescopic lenses. An NVD image is typically monochrome green, as green was considered to be the easiest color to see for prolonged periods in the dark.[2] Night vision devices may be passive, relying solely on ambient light, or may be active, using an IR (infrared) illuminator.
Night vision devices may be handheld or attach to helmets. When used with firearms, an IR laser sight is often mounted to the weapon. The laser sight produces an infrared beam that is visible only through an NVD and aids with aiming.[3] Some night vision devices are made to be mounted to firearms. These can be used in conjunction with weapon sights or standalone; some thermal weapon sights have been designed to provide similar capabilities.[4]
These devices were first used for night combat in World War II and came into wide use during the Vietnam War.[5] The technology has evolved since then, involving "generations"[6] of night-vision equipment with performance increases and price reductions. Consequently, though they are commonly used by military and law enforcement agencies, night vision devices are available to civilian users for applications including aviation, driving, and demining.[7]
In 1929 Hungarian physicist Kálmán Tihanyi invented an infrared-sensitive electronic television camera for anti-aircraft defense in the UK.[8] Night vision technology prior to the end of World War II was later described as Generation 0.[5]
Night-vision devices were introduced in the German Army as early as 1939[citation needed] and were used in World War II. AEG started developing its first devices in 1935. In mid-1943, the German Army began testing infrared night-vision devices and telescopic rangefinders mounted on Panther tanks. Two arrangements were constructed. The Sperber FG 1250 ("Sparrow Hawk"), with a range of up to 600 m, had a 30 cm infrared searchlight and an image converter operated by the tank commander.
From late 1944 to March 1945 the German military conducted successful tests of FG 1250 sets mounted on Panther Ausf. G tanks (and other variants). During the war, approximately 50 (or 63) Panthers were equipped with the FG 1250 and saw combat on both the Eastern and Western Fronts. The "Vampir" man-portable system for infantry was used with StG 44 assault rifles.[9]
Parallel development occurred in the US. The M1 and M3 infrared night-sighting devices, also known as the "sniperscope" or "snooperscope", saw limited service with the US Army in World War II[10] and in the Korean War, to assist snipers.[5] These were active devices, using an infrared light source to illuminate targets. Their image-intensifier tubes used an anode and an S-1 photocathode, made primarily of silver, cesium, and oxygen, and electrostatic inversion with electron acceleration produced gain.[11]
An experimental Soviet device called the PAU-2 was field-tested in 1942.
In 1938 the British Admiralty assumed responsibility for British military infra-red research. They worked first with Philips until the fall of the Netherlands, then with Philips' UK subsidiary Radio Transmission Equipment Ltd., and finally with EMI, who in early 1941 provided compact, lightweight image converter tubes. By July 1942 the British had produced a binocular apparatus called 'Design E'. This was bulky, needing an external power pack generating 7,000 volts, but saw limited use with amphibious vehicles of 79th Armoured Division in the 1945 crossing of the Rhine. Between May and June 1943, 43rd (Wessex) Infantry Division trialled man-portable night vision sets, and the British later experimented with mounting the devices to Mark III and Mark II(S) Sten submachine guns. However, by January 1945 the British had only made seven infra-red receiver sets. Although some were sent to India and Australia for trials before the end of 1945, by the Korean War and Malayan Emergency the British were using night vision equipment supplied by the United States.[12]
Early examples include:
After World War II, Vladimir K. Zworykin developed the first practical commercial night-vision device at Radio Corporation of America, intended for civilian use. Zworykin's idea came from a former radio-guided missile.[15] At that time, infrared was commonly called black light, a term later restricted to ultraviolet. Zworykin's invention was not a success due to its large size and high cost.[16]
First-generation passive devices developed by the US Army in the 1960s were introduced during the Vietnam War. They were an adaptation of earlier active technology and relied on ambient light instead of using an extra infrared light source. Using an S-20 photocathode, their image intensifiers amplified light around 1,000-fold,[17] but they were quite bulky and required moonlight to function properly.
Examples:
1970s second-generation devices featured an improved image-intensifier tube using a micro-channel plate (MCP)[21] with an S-25 photocathode.[11] This produced a much brighter image, especially around the edges of the lens. This led to increased clarity in low ambient-light environments, such as moonless nights. Light amplification was around 20,000.[17] Image resolution and reliability improved.
Examples:
Later advances brought GEN II+ devices (equipped with better optics, SUPERGEN tubes, improved resolution and better signal-to-noise ratios), though the label is not formally recognized by the NVESD.[24]
Third-generation night-vision systems, developed in the late 1980s, maintained the MCP from Gen II, but used a gallium arsenide photocathode, with improved resolution. GA photocathodes are primarily manufactured by L3Harris Technologies and Elbit Systems of America and imaged light from 500-900 nm.[25] In addition, the MCP was coated with an ion barrier film to increase tube life. However, the ion barrier allowed fewer electrons to pass through. The ion barrier increased the "halo" effect around bright spots or light sources. Light amplification (and power consumption) with these devices improved to around 30,000–50,000.[17]
Examples:
Autogating (ATG) rapidly switches the power supply's voltage to the photocathode on and off. These switches are rapid enough that they are not detectable to the human eye and peak voltage supplied to the night vision device is maintained.[29] This reduces the "duty cycle" (ie. the amount of time that the tube has power running through it) which increases the device's lifespan.[30] Autogating also enhances the Bright-Source Protection (BSP), which reduces the voltage supplied to the photocathode in response to ambient light levels. Automatic Brightness Control (ABC) modulates the amount of voltage supplied to the microchannel plate (rather than the photocathode) in response to ambient light. Together, BSP and ABC (alongside autogating) serves to prevent temporary blindness for the user and prevent damage to the tube when the night vision device is exposed to sudden bright sources of light,[29] like a muzzle flash or artificial lighting.[30] These modulation systems also help maintain a steady illumination level in the user's view that improves the ability to keep "eyes on target" in spite of temporary light flashes. These functions are especially useful for pilots, soldiers in urban environments, and special operations forces who may be exposed to rapidly changing light levels.[30][31]
OMNI, or OMNIBUS, refers to a series of contracts through which the US Army purchased GEN III night vision devices. This started with OMNI I, which procured AN/PVS-7A and AN/PVS-7B devices, then continued with OMNI II (1990), OMNI III (1992), OMNI IV (1996), OMNI V (1998), OMNI VI (2002), OMNI VII (2005),[32] OMNI VIII, and OMNI IX.[33]
However, OMNI is not a specification. The performance of a particular device generally depends upon the tube which is used. For example, a GEN III OMNI III MX-10160A/AVS-6 tube performs similarly to a GEN III OMNI VII MX-10160A/AVS-6 tube, even though the former was manufactured in ~1992 and the latter ~2005.[33][34]
One particular technology, PINNACLE is a proprietary thin-film microchannel plate technology created by ITT that was included in the OMNI VII contract. The thin-film improves performance.[34]
GEN III OMNI V–IX devices developed in the 2000s and onward can differ from earlier devices in important ways:
The consumer market sometimes classifies such systems as Generation 4, the United States military describes these systems as Generation 3 autogated tubes (GEN III OMNI V-IX). Moreover, as autogating power supplies can be added to any previous generation of night-vision devices, autogating capability does not automatically put the devices in a particular OMNI classification. Any postnominals appearing after a generation type (i.e., Gen II+, Gen III+) indicate improvement(s) over the original specification's requirements.[37]
Examples:
Figure of merit (FoM) is a quantitative measure of a NVD's effectiveness and clarity. It is calculated using the number of line pairs per millimeter that a user can detect multiplied by the image intensifier's signal-to-noise (SNR) ratio.[39][40][33][41]
In the late 1990s, innovations in photocathode technology significantly increased the SNR, with new tubes surpassing Gen 3 performance.
By 2001, the United States federal government concluded that a tube's generation was not a determinant performance factor, obsoleting the term as a basis of export regulations.
The US government has recognized the fact that the technology itself makes little difference, as long as an operator can see clearly at night. Consequently, the United States bases export regulations directly on the figure of merit.
ITAR regulations specify that US-made tubes with a FOM greater than 1400 are not exportable; however, the Defense Technology Security Administration (DTSA) can waive that policy on a case-by-case basis.
Fusion night vision is a newer advance in night vision technology which combines I² (image intensification) with thermal imaging, which functions in the medium (MWIR 3-5 μm) and/or long (LWIR 8-14 μm) wavelength range.[42] Initial models appeared in the 2000s and progressed in the 2010s.[32] Some devices are dedicated fusion devices while others are clip-on thermal imagers which can add a thermal overlay to standard I² night vision devices.[43] Fusion technologies combines the strengths of traditional I², which is excellent for navigation and discernment of fine details, with the strengths of thermal imaging, which excels in spotting the heat signatures of targets. Fusion systems have offered a number of different imaging modes including "fused" night vision with thermal overlay, night vision only, thermal only, and various special fusion modes like outline (which outlines objects that have thermal signatures) or "decamouflage", which highlights all objects that are of near-human temperatures. Fusion devices do struggle with weight and power usage and are often heavier and have shorter run times than contemporary I²-only devices.[44]
Aside from fusion of I² and thermal imaging within a single device, some users have tried using an I² device over one eye and a thermal device over the other eye, relying on the human visual system to provide a binocular combined view of the two. Some, but not all, thermal imaging systems can also be viewed through a night vision device (ie. lining up the thermal imager in front of the I² night vision device) to produce a form of fusion vision.[43][45]
Examples:
Out of Band (OOB) refers to night vision technologies which operate outside of the 500-900 nm NIR (near infrared) range that traditional Gen III gallium arsenide tubes detect. Imaging outside the usual spectrum is possible with dedicated OOB image intensifier tubes or with clip-on devices. Two examples include Photonis' 4G HyMa (Hybrid Multi-Alkali) image intensifier tubes (bandwidth of 350-1100 nm, from near UV to IR) and Safran Optics 1's AN/PAS-34 E-COSI (Enhanced Clip-On SWIR Imager), which clips onto standard night vision devices and provides an overlay (in the 900-1700 nm range), respectively.[46]
OOB provides several advantages. First, OOB imaging makes better use of ambient light; while a standard Gen III device can only intensify light in the 500-900 nm NIR range, an OOB device also intensifies any UV light or SWIR light in the environment. As a result, an OOB device might be able to see more on a starlit night than a standard GEN III device could. Second, OOB imaging can help JTACs and other FACs when marking targets with a laser designator. Many laser designators use 1064nm light, which is barely visible to standard Gen III devices, so ground personnel may need to use a separate "see-spot" device to visually confirm that the designator's targeting laser is on target. OOB night vision devices, however, can easily image the 1064nm range.[25][47]
Third, OOB light is not visible to most commercially available night vision devices. Despite ITAR restrictions, night vision technologies have proliferated among peer and near-peer countries and have also made their way into terrorist hands. For example, there has been documented use of night vision equipment by the Taliban Red Unit.[48] As a result, if friendly forces are using night vision equipment like IR illuminators, IR strobes, IR lasers, etc. then hostile forces using night vision equipment could spot them as well. OOB strobes, illuminators, and lasers, on the other hand, are easily visible when using OOB night vision but much more difficult to spot with current Gen III night vision equipment as they appear faintly if at all (depending on wavelength and intensity).[49][50]
Additionally, depending on the wavelengths covered by an OOB imaging device, users might be able to observe the lasers used in laser rangefinders as they often operate in the 1550nm range.[51]
Examples (ground personnel, helmet-mounted imagers):
Examples (ground personnel, weapon-mounted lasers):
Night vision devices, whether monocular or binocular, typically have a limited field of view (FoV); the commonly used AN/PVS-14 has a FoV of 40°[66] which is rather less than the 95° monocular horizontal FoV and 190° binocular horizontal FoV that humans possess.[67] Due to the limited FoV, users must visually scan about to fully check their surroundings, which is a time consuming process. This limitation is particularly evident when using night vision devices for flying, driving, or CQB where split second decisions must be made. Because of these limitations, many SF/SOF operators preferred to use white light rather than night vision when conducting CQB.[68] As a result, much time and effort has gone into research to develop a wider FoV solution for night vision devices. As of 2021, there were three primary methods for increasing peripheral vision in night vision devices (each with their own advantages and disadvantages):
Panoramic night vision goggles (PNVG) increase field of view by increasing the number of sensors: if tubes are generally limited to 40°, then one can add more tubes to increase peripheral vision. This solution works well and does not compromise device performance or visual clarity but comes at the cost of size, weight, power requirements, and complexity.[69] A well-known set of peripheral NVGs is the GPNVG-18 (Ground Peripheral Night Vision Goggle), which was used in the raid in Abbottabad that killed Osama bin Laden.[70] These goggles, and the aviation AN/AVS-10 PNVG from which they were derived, offer a 97° FoV.[68]
Foveated night vision (F-NVG) uses specialized WFoV optics to increase the field of view through a night vision intensifier tube. The fovea refers to the part of the retina which is responsible for central vision. These night vision devices have users still look "straight through" the tubes so light passing through the center of the tube falls on the foveal retina, as is the case with traditional binocular NVGs. While these devices increase FoV, it comes at the price of image quality and edge distortions.[69] A US Naval contract for US$47.6 million was awarded to Kent Optronics to retrofit AN/PVS-15 units with WFoV optics that expanded them to 80° FoV with less than 4% distortion.[71][72][73]
Diverging image tube (DIT) night vision increases FoV by positioning the night vision tubes so they are no longer parallel but are angled slightly outward. This increases peripheral FoV but causes distortion and reduced image quality. Unfortunately, optical clarity is best when looking through the center of an image intensifier tube. With DIT, users are no longer looking "straight through" the center of the tubes (which provides the clearest images) and light passing through the center of the tubes no longer falls on the fovea (the area of clearest vision). The AN/PVS-25 was one such example of DIT night vision from the late 2000s.[69] The WFoV BNVD is a variant of the AN/PVS-31A which incorporates both F-NVG and DIT-NVG concepts: the foveal WFoV optics increase the FoV of each tube from 40° to 55°, while the slight angulation of the tubes positions them so there is a 40° overlap of binocular vision in the center and a total 70° bi-ocular FoV. With the performance of the modified AN/PVS-31A tubes used, the WFoV BNVD has a FoM of 2706 which is better than the FoM in both the GPNVG-18 and the standard AN/PVS-31A.[74][69]
Examples:
Some night vision devices, including several of the ENVG (AN/PSQ-20) models, are "digital". Introduced in the late 2000s, these allow electronic transmission of the device's night vision view, though this often comes at the price of size, weight, power usage.[32]
Advancements in high-sensitivity digital camera technology has made it possible to produce NVGs that use a camera-display pair instead of an image intensifier. At the low end of the market, these devices can offer Gen-1-equivalent quality at a lower cost.[76] At the higher end, SiOnyx has produced digital color NVGs. The "Opsin" of 2022 has a form factor and helmet weight similar to that of an AN/PVS-14, but requires a separate battery pack with a shorter battery life and remains inferior in sensitivity.[77][78] Being a camera-based design, it can however tolerate bright light and process a wider range of wavelengths.[79]
Ceramic Optical Ruggedized Engine (CORE) is a technology which was first shown at the 2012 SHOT Show in Las Vegas, NV by Armasight.[80] CORE produces a higher-performance Gen 1 tubes. The main difference between CORE tubes and standard Gen 1 tubes is introduction of a ceramic plate instead of a glass one. This plate is produced from specially formulated ceramic and metal alloys. Edge distortion is improved, photo sensitivity is increased, and the resolution can be as high as 60 lp/mm. CORE is still considered[by whom?] Gen 1, as it does not utilize a microchannel plate.
Scientists at the University of Michigan have developed a contact lens that can act as a night-vision device. The lens has a thin strip of graphene between layers of glass that reacts to photons to make dark images look brighter. Current prototypes only absorb 2.3% of light, so the percentage of light pickup has to rise before the lens can be viable. The graphene technology can be expanded into other uses, like car windshields, to improve night-driving. The US. Army is interested in the technology to potentially replace night-vision goggles.[81]
The Sensor and Electron Devices Directorate (SEDD) of the US Army Research Laboratory developed quantum-well infrared detector (QWID) technology. This technology's epitaxial layers, which result in diode formation, compose a gallium arsenide or aluminum gallium arsenide system (GaAs or AlGaAs). It is particularly sensitive to infrared waves that are mid-long lengths. The Corrugated QWIP (CQWIP) broadens detection capacity by using a resonance superstructure to orient more of the electric field parallel, so that it can be absorbed. Although cryogenic cooling between 77 K and 85 K is required, QWID technology is considered[by whom?] for constant surveillance viewing due to its claimed low cost and uniformity in materials.[82]
Materials from the II–VI compounds, such as HgCdTe, are used for high-performing infrared light-sensing cameras. In 2017 the US Army Research Labs in collaboration with Stony Brook University developed an alternative within the III–V family of compounds. InAsSb, a III–V compound, is commonly used commercially for opto-electronics in items such as DVDs and cell phones. Low cost and larger semiconductors frequently cause atomic spacing to decrease leading to size mismatch defects.[clarify] To counteract this possibility in implementing InAsSb, scientists added a graded layer with increased atomic spacing and an intermediate layer of the substrate GaAs to trap any potential defects. This technology was designed with night-time military operations in mind.[83]
The Soviet Union, and after 1991 the Russian Federation, have developed a range of night-vision devices. Models used after 1960 by the Russian/Soviet Army are designated 1PNxx (Russian: 1ПНxx), where 1PN is the GRAU index of night-vision devices. The PN stands for pritsel nochnoy (Russian: прицел ночной), meaning "night sight", and the xx is the model number. Different models introduced around the same time use the same type of batteries and mechanism for mounting on the weapon. The multi-weapon models have replaceable elevation scales, with one scale for the ballistic arc of each supported weapon. The weapons supported include the AK family, sniper rifles, light machine guns and hand-held grenade launchers.
The Russian army has also contracted the development of and fielded a series of so-called counter-sniper night sightsRussian: Антиснайпер, romanized: Antisnayper). The counter-sniper night sight is an active system that uses laser pulses from a laser diode to detect reflections from the focal elements of enemy optical systems and estimate their range. The vendor claims that this system is unparalleled:[89]
(