A few years back I found a good glossary of terms used with Night Vision and posted to another site with a dedicated NV section. I think it’s appropriate for this thread to get people familiarized with terms and as a resource to reference when reading “NV” tagged threads.
Automatic Brightness Control (ABC)
An electronic feature that automatically reduces voltages to the Microchannel Plate to keep the image intensifier’s brightness within optimal limits and protects the tube. The effect of this can be seen when rapidly changing from low-light to high-light conditions; the image gets brighter and then, after a momentary delay, suddenly dims to a constant level.
Auto-Gated Power Supply
When the power supply is “Auto-Gated,” it means the system is turning itself on and off at a very rapid rate. This, combined with a thin film attached to the Microchannel plate (an ion barrier) reduces blooming. While “blooming” can be noticeably less on systems with a thin film layer, systems with thicker film layers can be perfectly acceptable depending on the end user’s application. Deciding which night vision goggle is better should not be based solely on blooming.
These are common blemishes in the image intensifier of the NVD or can be dirt or debris between the lenses of the NVG. Black spots that are in the image intensifier do not affect the performance or reliability of a night vision device and are inherent in the manufacturing processes. Every night vision image intensifier tube is different.
These can be defects in the image area produced by the NVG. A flaw in the film on the Microchannel plate causes this condition. A bright spot is a small, non-uniform, bright area that may flicker or appear constant. Bright spots usually go away when the light is blocked out and are cosmetic blemishes that are signal induced.
Viewing a single image source with both eyes (example: watching a television set).
Viewing a scene through two channels; i.e. one channel per eye.
Loss of the entire night vision image, parts of it, or small parts of it, due to intensifier tube overloading by a bright light source. Also, known as a “halo” effect, when the viewer sees a “halo” effect around visible light sources. When such a bright light source comes into the night vision device’s view, the entire night vision scene, or parts of it, becomes much brighter, “whiting out” objects within the field of view. Blooming is common in Generation 0 and 1 devices. The lights in the image to the right would be considered to be “blooming”.
Bright-Source Protection (BSP) – Highlight Cut-Off
An electronic function that reduces the voltage to the photocathode when the night vision device is exposed to bright light sources such as room lights or car lights. BSP protects the image tube from damage and enhances its life; however, it also has the effect of lowering resolution when functioning except for the Pinnacle Autogated Units which maintain the systems resolution.
A standard still and video camera lens thread size for mounting to the body of a camera. Usually 1/2″ or 3/4″ in diameter.
COMSPEC (Commercial Specification)
A term used to describe image tube quality, testing and inspection done by the original equipment manufacturer (OEM).
An irregular pattern of dark thin lines in the field of view either throughout the image area or in parts of the image area. Under the worst-case condition, these lines will form hexagonal or square wave-shape lines.
Daylight Lens Cover
Usually made of soft plastic or rubber with a pinhole that allows a small amount of light to enter the objective lens of a night vision device. This should be used for training purposes only, and is not recommended for an extended period of time. Near field focus only useable in this fashion.
Daylight Training Filter
A glass filter assembly designed to fit over the objective lens of a night vision device. The filter reduces light input to a safe (night-time) level, allowing safe extended daytime use of the night vision device.
The unit of measure used to define eye correction or the refractive power of a lens. Usually, adjustments to an optical eyepiece accommodate for differences in individual eyesight. Most ITT systems provide a +2 to -6 Diopter range.
There are two types of distortion found in night vision systems. One type is caused by the design of the optics, or image intensifier tube, and is classical optical distortion. The other type is associated with manufacturing flaws in the fiber optics used in the image intensifier tube.
Classical Optical Distortion: Classical optical distortion occurs when the design of the optics or image intensifier tube causes straight lines at the edge of the field of view to curve inward or outward. This curving of straight lines at the edge will cause a square grid pattern to start to look like a pincushion or barrel. This distortion is the same for all systems with the same model number. Good optical design normally makes this distortion so low that the typical user will not see the curving of the lines.
Fiber Optics Manufacturing Distortions: Two types of fiber optics distortions are most significant to night vision devices: S-distortion and shear distortion:
S-Distortion: Results from the twisting operation in manufacturing fiber-optic inverters. Usually S-distortion is very small and is difficult to detect with the unaided eye.
Shear Distortion: Can occur in any image tube that uses fiber-optic bundles for the phosphor screen. It appears as a cleavage or dislocation in a straight line viewed in the image area, as though the line were “sheared”.
Equivalent Background Illumination (EBI)
This is the amount of light you see through a night vision device when an image tube is turned on but no light is on the photocathode. EBI is affected by temperature; the warmer the night vision device, the brighter the background illumination. EBI is measured in lumens per square centimeter (lm/cm2). The lower the value the better. The EBI level determines the lowest light level at which an image can be detected. Below this light level, objects will be masked by the EBI.
There is a defect in the image area of the NVG. Edge glow is a bright area (sometimes sparkling) in the outer portion of the viewing area.
A steady or fluctuating pinpoint of bright light in the image area that does not go away when all light is blocked from the objective lens. The position of an emission point within the field of view will not move. If an emission point disappears or is only faintly visible when viewing under brighter nighttime conditions, it is not indicative of a problem. If the emission point remains bright under all lighting conditions, the system needs to be repaired. Do not confuse an emission point with a point of light source in the scene being viewed.
The distance a person’s eyes must be from the last element of an eyepiece in order to achieve the optimal image area.
The diameter of the imaged area when viewed through an optic
Figure of Merit (FOM)
Image Intensification tube specification designation, calculated on line pair per mm x signal to noise.
Fixed-Pattern Noise (FPN)
A faint hexagonal (honeycomb) pattern throughout the image area that most often occurs under highlights conditions. This pattern is inherent in the structure of the Microchannel plate and can be seen in virtually all Gen 2 and Gen 3 systems if the light level is high enough.
A unit of brightness equal to one footcandle at a distance of one foot.
Also called brightness gain or luminance gain. This is the number of times a night vision device amplifies light input. It is usually measured as tube gain and system gain. Tube gain is measured as the light output (in fL) divided by the light input (in fc). This figure is usually expressed in values of tens of thousands. If tube gain is pushed too high, the tube will be “noisier” and the signal-to-noise ration many go down. U.S. military Gen 3 image tubes operate at gains of between 20,000 and 45,000. On the other hand, system gain is measured as the light output (fL) divided by the light input (also fL) and is what the user actually sees. System gain is usually seen in the thousands. U.S. military systems operate at 2,000 to 3,000. In any night vision system, the tube gain is reduced by the system’s lenses and is affected by the quality of the optics or any filters. Therefore, system gain is a more important measurement to the user.
Gallium Arsenide (GaAs)
The semiconductor material used in manufacturing the Gen 3 photocathode. GaAs photocathodes have a very high photosensitivity in the spectral region of about 450 to 950 nanometers (visible and near-infrared region).
Two technologies are referenced as night vision; image intensification and thermal imaging (see definitions). Because of cost and the fact that image intensifier scenes are easier to interpret than thermal (thermal images show targets as black or white – depending upon temperature – making it more difficult to recognize objects), the most widely used night vision aid in law enforcement is image intensification (l²) equipment. To date, there have been four generations of l² devices, identified as Gen 0, Gen 1, Gen 2, and Gen 3. Developmental laboratory work is on going, and the U.S. military may designate the resulting as Gen 4. However, no definition for Gen 4 presently exists.
Halo is the circular region around a bright light that appears “brighter” – It’s caused by elastic collisions of electrons with the MCP surface which subsequently then bounce off and down another hole. Halo’s are the same size all over the screen and the size is dictated by the distance between the photocathode and the MCP. Basically, it’s the round circle around lights when you look at them with Night Vision and it’s generally used as an indication that you’re looking at something that’s too bright.
An image intensifier protection feature incorporating a sensor, microprocessor and circuit breaker. This feature will turn the system off during periods of extreme bright light conditions.
The distance between the user’s eyes (pupils) and the adjustment of binocular optics to adjust for differences in individuals. Improperly adjusted binoculars will display a scene that appears egg-shaped or as a reclining figure-8.
The distance between the user’s pupils (eyeball centers). The 95th percentile of US military personnel falls within the 55 to 72mm range of IPD.
Many night vision devices incorporate a built-in infrared (IR) diode that emits invisible light or the illuminator can be mounted on to it as a separate component. The unaided eye cannot see IR light; therefore, a night vision device is necessary to see this light. IR Illuminators provide supplemental infrared illumination of an appropriate wavelength, typically in a range of wavelengths (e.g. 730nm, 830nm, 920nm), and eliminate the variability of available ambient light, but also allow the observer to illuminate only specific areas of interest while eliminating shadows and enhancing image contrast.
High-power devices providing long-range illumination capability. Ranges of several thousand meters are common. Most are not eye-safe and are restricted in use. Consult FDA CFR Title 21 for specific details and restrictions.
Area outside the visible spectrum that cannot be seen by the human eye (between 700 nanometers and 1 millimeter). The visible spectrum is between 400 and 700 nanometers.
ITAR (International Traffic in Arms Regulations)
ITAR represents a set of US Government regulations that control the export of defense-related materials, articles, and services on the United States Munitions List. These regulations implement the provisions of the Arms Export Control Act, and are described in Title 22 (Foreign Relations), Chapter I (Department of State), Subchapter M of the Code of Federal Regulations. The Department of State Interprets and enforces ITAR. Its goal is to safeguard US National Security and further US Foreign Policy objectives. Basically, ITAR dictates that any defense related items (including Night Vision Equipment and IR Equipment) cannot be exported from the United States in any way, without express permission from the US Department of State. Failing to follow ITAR will result in felony charges which can lead to heavy fines and/or prison sentences.
LED (Light-Emitting Diode)
LED’s are electronic light sources based on the semiconductor diode. When the diode is forward biased, electrons recombine with holes, releasing energy in the form of light. This is called Electroluminescence. The color of the light is determined by the energy gap of the semiconductor. LED’s have many advantages over traditional incandescent light sources including lower energy consumption, longer lifetime, more robustness, smaller size, and faster switching.
Lp/mm (Line Pairs per Millimeter)
Units used to measure image intensifier resolution. Usually determined from a 1951 U.S. Air Force Resolving Power Test Target. The target is a series of different-sized patterns composed of three horizontal and three vertical lines. A user must be able to distinguish all the horizontal and vertical lines and the spaces between them. Typically, the higher the line pair, the better the image resolution. Generation 3 tubes generally have a range of 64 – 72 lp/mm, although line pair measurement does not indicate the generation of the tube. Some Generation 2+ tubes measure 28-38 lp/mm, (Gen 2 SHP at 54-59 lp/mm typically), while a Generation 1+ tube may have measure at 40 lp/mm.
Denotes the photons perceptible by the human eye in one second.
A single channel optical device.
Term for the North Atlantic Treaty Organization STANdard AGreement. This can be described as an international MILSPEC
mA/W (Milliamps per Watt)
The measure of electrical current (mA) produced by a photocathode when exposed to a specified wavelength of light at a given radiant power (watt).
MCP (Microchannel Plate)
A metal-coated glass disk that multiplies the electrons produced by the photocathode. An MCP is found only in Gen 2 or Gen 3 systems. MCPs eliminate the distortion characteristic of Gen 0 and Gen 1 systems. The number of holes (channels) in an MCP is a major factor in determining resolution. ITT Industries’ MCPs have 10.6 million holes or channels compared to the previous standard of 3.14 million.
A microwatt is equal to one millionth of a watt. A watt is a derived unit of power in the International System of Units (SI) and measures the rate of energy conversion. One watt is equivalent to 1 joule of energy per second.
A unit of measurement used to determine the divergence of a laser beam. The miliradian is equal to 0.001 radians and corresponds to an error of 1 meter at 1,000 meters.
A milliwatt is equal to one thousandth of a watt. A watt is a derived unit of power in the International System of Units (SI) and measures the rate of energy conversion. One watt is equivalent to 1 joule of energy per second
A unit of length in the metric system equal to one billionth of a meter. Nanometers are the most common unit used to describe the manufacturing technology used in the semiconductor industry and the most common unit to describe the wavelength of light.
The shortest wavelengths of the infrared region, nominally 750 to 2,500 nanometers. Also see How Thermal Imaging and Infrared Technology Works.
NSN (National Stock Number)
13-digit code identifying all ‘standardized material items of supply’ as they have been recognized by the United States Department of Defense. National Stock Numbers have come to used in all NATO countries pursuant to the NATO Standardization Agreements (STANAGs).
The input surface of an image intensifier tube that absorbs light energy (photons) and in turn releases electrical energy (electrons) in the form of an image. The type of material used is a distinguishing characteristic of the different generations.
Photocathode sensitivity is a measure of how well the image intensifier tube converts light into an electronic signal so it can be amplified. The measuring units of photocathode sensitivity are micro-amps/lumen (µA/lm) or microamperes per lumen. This criterion specifies the number of electrons released by the Photocathode (PC). PC response is always measured in isolation with no amplification stage or ion barrier (film). Therefore, tube data sheets (which always carry this “raw” figure) do not reflect the fact that over 50% of those electrons are lost in the ion barrier. While for most latest 3rd generation image intensifiers the photo response is in the 1800 µA/lm (2000 µA/lm for the latest Omni VI Pinnacle tubes), the actual number is more like 900 µA/lm.
The ability of an image intensifier or night vision system to distinguish between objects close together. Image intensifier resolution is measured in line pairs per millimeter (lp/mm) while system resolution is measured in cycles per miliradian. For any particular night vision system, the image intensifier resolution will remain constant while the system resolution can be affected by altering the objective or eyepiece optics by adding magnification or relay lenses. Often the resolution in the same night vision device is very different when measured at the centre of the image and at the periphery of the image. This is especially important for devices selected for photograph or video where the entire image resolution is important. Measured in line pairs per millimeter (lp/mm).
Signal-to-Noise Ratio (SNR)
A measure of the light signal reaching the eye divided by the perceived noise as seen by the eye. A tube’s SNR determines the low light resolution of the image tube; therefore, the higher the SNR, the better the ability of the tube to resolve objects with good contrast under low-light conditions. Because SNR is directly related to the photocathode’s sensitivity and also accounts for phosphor efficiency and MCP operating voltage, it is the best single indicator of an image intensifier’s performance
Also known as electronic noise. A faint, random, sparkling effect throughout the image area. Scintillation is a normal characteristic of Microchannel plate image intensifiers and is more pronounced under low-light-level conditions
The image tube output that produces the viewable image. Phosphor (P) is used on the inside surface of the screen to produce the glow, thus producing the picture. Different phosphors are used in image intensifier tubes, depending on manufacturer and tube generation. P-43 is standard Green Phosphor and P-45 is White Phosphor. There are several different Phosphor colors in use today for various systems.
Stereoscopic Night Vision
When two views or photographs are taken through one device. One view/photograph represents the left eye, and the other the right eye. When the two photographs are viewed in a stereoscopic apparatus, they combine to create a single image with depth and relief. Sometimes this gives two perspectives. However, it is usually not an issue because the object of focus is far enough away for the perspectives to blend into one.
Equal to tube gain minus losses induced by system components such as lenses, beam splitters and filters.
Variable Gain Control
Allows the user to manually adjust the gain control ( basically like a dim control ) in varying light conditions. This feature sets the PVS-14 apart from other popular monoculars that do not offer this feature. PVS-4 25mm Photocathode tube devices (PVS-4 Starlight Scope) also have this feature.
There are several sources for night vision glossaries, but I will cite this source, although I have modified it slightly and removed references to weapons - http://nightvisionop...ision-glossary/
A couple other useful terms to understand and several can describe use of night vision for astronomy
I^2 Astronomy - Image Intensified Astronomy
IIE - Image Intensified Eyepiece, Image Intensifier Eyepiece
NVD - Night Vision Device (not to be confused with the NVD Micro device which stands for Night Vision Depot Micro Monocular, a very popular monocular with built-in c-mount)
NV Astronomy - Night Vision Astronomy