GLOSSARY OF NIGHT VISION TERMINOLOGY
See Also: How
Night Vision Works
See Also: Frequently Asked Night
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 protect 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. They are like diamonds. See image to the right. See also - How to Buy Night Vision Equipment
These can be defects in the image area produced by the NVG. This condition is caused by a flaw in the film on the microchannel plate. 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, become 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) - High-Light 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.
The alignment of a weapon aiming device to the bore of the weapon.
See also Zeroing.
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.
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
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 high-light 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
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 "noiser" 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
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.
The first night vision aids (also called Generation Zero or Gen
0) were sniper scopes that came into use during World War II and
the Korean conflict. These were not true image intensifiers, but
rather image converters, which required a source of invisible
infrared (IR) light mounted on or near the device to illuminate
the target area.
The "starlight scopes" developed during the early 1960's
for use in Vietnam were the first Generation (Gen 1) of image
intensifier devices. In Gen 1 night vision units, three image
intensifiers were connected in a series, making the units longer
and heavier than future night vision units would be. Gen 1 equipment
produced an image that was clear in the center of the field of
view but suffered from large optical distortion around the periphery.
Gen 1 equipment was also subject to "blooming". Most
low-cost imported night vision units use Gen 1 technology, though
often under the guise of a higher "generation".
1 Night Vision Goggle - MV-2MV
The development of the microchannel plate, or MCP, in the late
1960s brought on the second generation (Gen 2) in l² night
vision. The MCP accelerated and multiplied electrons which provided
the gain previously supplied by coupling three image intensifiers
together (Gen 1). The introduction of the MCP significantly reduced
size and weight for image intensifier tubes, enabling design of
smaller night vision goggles and hand-held devices. The MCP also
provided much more robust operation when bright lights entered
the field of view. The Gen 2 tubes used the same tri-alkali photocathode
as the Gen 1 devices. This generation was implemented to reflect
the change in how the light was amplified (MCP versus three-stage
2 Night Vision Goggles -MV/PVS-7B
Third-generation (Gen 3) image intensifiers were developed in
the mid-1970s and became available during the early 1980s. Gen
3 introduced two major technological improvements: the gallium
arsenide (GaAs) photocathode and the ion barrier coating to the
microchannel plate. The GaAs photocathode increases the tube's
sensitivity to light from the near-infrared range of the spectrum,
enables it to function at greater detection distances, and improves
system performance under low-light conditions. Application of
a metal-oxide ion barrier to the MCP increases the life of the
image tube. The operational life of Gen 3 tubes is in excess of
10,000 hours, compared to that of Gen 2 tubes which is about 2,000
to 4,000 hours. This generation was implemented to reflect the
change in the photocathode (tri-alkali replaced with GaAs).
3 Night Vision Monoculars - ITT Night Vision
Gated Filmless Technology
Gated filmless technology was created in 1998, but without the reliability required for military delivery. By removing the ion barrier film and "gating" the system power supply, the technology demonstrated substantial increases in target detection range and resolution. In the process, however, it was discovered by ITT, that the same performance results could be achieved using a Generation 3 tube, but with a thinner ion barrier film and a auto-gated power supply, without sacrificing reliability and life-span of the intensifier tube. See also: Myth vs. Fact: Generation 4 directly below.
Myth vs. Fact: Generation 4
Some say that generation (Gen) 4 is the most advanced night vision you can buy. This is not the case. To dispel this myth, let's start with the basics. There are four Generations of night vision; however, they are Gen 0-3, not Gen 1-4. Historically, the U.S. Army has defined each Generation of night vision. In the late 90's the Army did define Gen 4 as the removal of the ion barrier film creating a "filmless" tube. This new advancement was to reduce halos while increasing sensitivity, signal-to-noise ratio (SNR) and resolution, for overall improved performance. While performance was improved, the lack of an ion barrier in Gen 4 tubes led to high failure rates, ultimately leading the U.S. Army to recant the existence of Gen 4 definition. Recognizing the high failure rates of Gen 4 tubes, ITT chose to improve upon the existing Gen 3 technology and create a "thin-filmed" tube. By keeping the protective ion barrier, but greatly reducing its thickness, ITT was able to maintain the reliability of Gen 3 while—at the same time—delivering on the Army's performance requirements intended for Gen 4. This innovation resulted in the production of the Gen 3 thin-filmed tube, which is now the highest performing Gen 3 tube available.
See also: ITT Night Vision Gen 3 PINNACLE® Tube Development and Night Vision Equipment Expert Blog
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 center). 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. IR light cannot be seen by the unaided eye;
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. Each IR laser should be marked with a
warning label like the one shown here. Consult FDA CFR Title 21
for specific details and restrictions.
I2 (Image Intensification) Collects
and intensifies the available light in the visible and near-infrared
spectrum. Offers a clear, distinguishable image under low-light
IR (Infrared) 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.
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, while a Generation 1+ tube may have measure at 40 lp/mm.
Lumen: Denotes the photons
perceptible by the human eye in one second.
A single channel optical device. See Night Vision Monoculars.
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
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.
The shortest wavelengths of the infrared region, nominally 750 to
2,500 nanometers. Also see How Thermal Imaging and Infrared Technology Works.
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 photoresponse 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).
Reticle (Reticle Pattern)
An adjustable aiming point or pattern (i.e. crosshair)
located within an optical weapon sight
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-20 phosphor is used in the systems offered in this catalogue
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.
Weaver Mounting System
A US weapon mounting system used for attaching sighting
devices to weapons. A Weaver Rail is a weapon-unique notched metal
rail designed to receive a mating throw-lever or Weaver Squeezer
attached to the sighting device
A method of boresighting an aiming device to a weapon and adjusting
to compensate for projectile characteristics at known distances.
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