Night Vision Glossary
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QDEF TECHNICAL // NIGHT VISION 101
Night Vision Glossary
Night vision comes with its own language. FOM, SNR, EBI, gain, autogating, blems, halo—the terminology can get confusing fast.
This glossary breaks down the most common night vision terms in plain English. If you're new to night vision, start here. You don't need an engineering background to understand what makes a night vision system perform.
NEW TO NIGHT VISION? // START WITH THESE
Automatic Brightness Control (ABC)
An electronic feature that automatically limits image brightness when the device encounters more light. It helps keep the image comfortable to view and protects the intensifier tube.
Plain English // The tube automatically turns itself down when things get bright.Autogating
Technology that rapidly switches voltage to the photocathode on and off. This allows an intensifier tube to respond better to changing or mixed lighting conditions.
Plain English // Helps night vision deal with headlights, streetlights, muzzle flashes, and other changing light sources.Binocular / Bino
A night vision system with two optical channels—one for each eye. Modern dual-tube systems such as the LLI MH-1 are binocular systems.
Plain English // Two tubes. One image presented to each eye.Biocular
A system where both eyes view the output from a single image source. The AN/PVS-7 is a well-known example.
Don't confuse it with // A binocular system, which uses separate channels for each eye.Black Spots / Blems
Dark cosmetic imperfections visible within the image. Some are inherent to the intensifier tube manufacturing process, while debris elsewhere in the optical system can sometimes look similar.
Good to know // Small cosmetic spots do not automatically mean a tube performs poorly.Black Boxing
A process where an image intensifier is allowed to operate for an extended period while completely deprived of external light. It is sometimes used when attempting to reduce certain temporary image artifacts.
Good to know // It is not a guaranteed repair for tube damage.Blooming
A bright light source overwhelming part of the intensified image, causing the bright area to appear enlarged or washed out.
Plain English // A bright light appears to spread beyond its actual size.Bright Spots
Small bright areas visible in the intensified image. Depending on their behavior and cause, they may be cosmetic artifacts or indicate an issue requiring further evaluation.
Bright-Source Protection (BSP)
A protection function that reduces voltage to the photocathode when the system encounters bright light. This helps protect the intensifier tube.
Burn-In
A persistent darker area or image artifact that can result from excessive exposure to a bright light source.
Plain English // Think of it as an image being partially "stained" into the tube.Chicken Wire
A visible pattern of thin lines that can appear across portions of the image. Under some conditions the pattern may look hexagonal or grid-like.
Collimation
The process of aligning the optical channels of a binocular or panoramic night vision system so the images presented to the user's eyes are properly aligned.
Why it matters // Poor collimation can make a binocular system uncomfortable or fatiguing to use.COMSPEC
Short for Commercial Specification. The term is generally used for image intensifier tubes sold under commercial rather than military procurement specifications.
Date of Manufacture (DOM)
The date an intensifier tube, housing, device, or other component was manufactured.
Daylight Lens Cover
An objective lens cover—often containing a small pinhole—that severely limits the amount of light entering the device.
Diopter
The eyepiece adjustment used to compensate for differences in the user's eyesight and bring the intensified image into focus for the eye.
Plain English // Focus the objective for the scene. Adjust the diopter for your eye.Distortion
Any visible warping of the image caused by the optical system, image intensifier, or internal fiber optics. Examples include barrel, pincushion, S-distortion, and shear distortion.
Edge Glow
An abnormal bright or glowing area near the outside edge of the intensified image.
Emission Point
A pinpoint of light generated within the intensifier rather than by the scene being viewed. An emission point can remain visible even when external light is blocked from the objective.
Equivalent Background Illumination (EBI)
A measurement representing background output generated by the intensifier itself. As ambient light becomes extremely low, this background can begin to compete with the actual image.
Remember // Lower EBI is generally better, especially in extremely dark conditions.Eye Relief
The distance between your eye and the eyepiece required to properly view the image through an optical system.
Field of View (FOV)
The amount of the scene you can see through the device at one time, normally expressed as an angle.
Example // A wider FOV lets you see more of the environment without moving your head.Figure of Merit (FOM)
A commonly referenced image intensifier performance number calculated by multiplying resolution by signal-to-noise ratio.
Formula // Resolution × SNR = FOM. Higher is generally better, but FOM does not tell the entire story.Filmed / Thin-Filmed / Unfilmed
Terms describing aspects of image intensifier construction, particularly the ion barrier associated with the microchannel plate and photocathode. Different manufacturers use different approaches to balance performance, durability, and tube life.
Good to know // Don't choose a tube based on this label alone. Actual tube performance specifications matter.Fixed-Pattern Noise (FPN)
A faint honeycomb or hexagonal pattern that can become visible in an intensified image, particularly under brighter conditions. It relates to the physical structure of the microchannel plate.
Focus Range
The range of distances over which the optical system can be brought into focus.
Gain
A measure of how much an image intensifier amplifies the available light. Gain can refer to the intensifier tube itself or to the complete optical system.
Plain English // Gain describes how much brighter the intensified image becomes.Manual Gain
A user-adjustable control that allows the brightness of the intensified image to be increased or decreased.
Don't confuse it with // Objective focus or diopter adjustment. Manual gain changes image brightness, not focus.Gallium Arsenide (GaAs)
A semiconductor material commonly associated with the photocathodes used in Gen 3 image intensifier technology.
Generation / Gen
A broad classification used to describe major stages in image intensifier technology. You'll commonly hear terms such as Gen 2 and Gen 3 when comparing night vision.
Important // Generation alone does not tell you how well an individual tube performs.Gen 2
A generation of image intensifier technology characterized by the use of a microchannel plate for electron multiplication. Modern Gen 2-family technology can offer very capable performance.
Gen 3
Image intensifier technology associated with gallium arsenide photocathodes and widely used in high-performance U.S. night vision systems.
"Gen 4"
A term sometimes used in night vision marketing, but not a currently recognized official U.S. generation classification.
Plain English // Don't shop for night vision simply because someone calls it "Gen 4."Ghosting
A temporary image artifact that can appear after exposure to a bright light source and may fade after the exposure is removed.
Halo
The glowing circular area visible around bright light sources when viewed through an image intensifier.
Remember // Lower halo values are generally preferred because bright sources obscure less of the surrounding image.Highlight Shutoff
A protective feature designed to shut down a night vision system when it is exposed to extremely bright conditions.
I² / Image Intensification
The technology used by traditional analog night vision to collect available visible and near-infrared light and amplify it into a visible image.
Image Intensifier Tube (IIT)
The electronic vacuum tube inside an analog night vision device that converts incoming light into electrons, multiplies those electrons, and turns them back into a visible image.
Plain English // The intensifier tube is the component that actually makes the night look brighter.Interpupillary Distance (IPD)
The distance between the centers of your pupils. Binocular night vision systems must position their eyepieces appropriately for the user's IPD.
IPD Stops
Mechanical stops on an articulating binocular housing that limit inward pod movement so the eyepieces can repeatedly return to the user's preferred position.
Infrared (IR)
Light outside the visible spectrum that cannot normally be seen by the human eye but can be detected by many night vision systems.
IR Illuminator
A device that projects infrared light to provide additional illumination for night vision.
Plain English // Think of it as a flashlight that your night vision can see.IR Laser
A laser emitting infrared energy that can be viewed through compatible night vision equipment.
Magnification
How much larger an object appears through an optical system. Most helmet-mounted night vision systems are designed around approximately 1× viewing so the environment appears life-size.
Microchannel Plate (MCP)
A thin component inside many image intensifier tubes containing millions of microscopic channels. Electrons entering those channels are multiplied many times before reaching the phosphor screen.
Plain English // The MCP is the electron multiplier inside the tube.MIL-SPEC
Short for Military Specification. The term indicates that a product or component is built or tested against an applicable military specification. The exact specification matters.
Monocular / Mono
A single-channel night vision device designed to present an intensified image to one eye. The PVS-14 is the best-known example.
Plain English // One tube, one optical channel.Near-Infrared (NIR)
The portion of the infrared spectrum closest to visible light. Image intensifiers can respond to wavelengths extending beyond what the human eye can see.
Nitrogen Purge
The process of displacing moisture-containing air inside a night vision device with dry nitrogen after assembly or service.
Why it matters // It helps reduce internal moisture and the possibility of internal fogging.NODs
Common shorthand for Night Observation Devices and often used casually to refer to night vision goggles in general.
NVG
Night Vision Goggle. A common general abbreviation for head- or helmet-mounted night vision.
Pano / Panoramic Night Vision
A multi-channel night vision system designed to provide a significantly wider field of view than conventional monocular or binocular systems. Quad-tube systems are the most familiar example.
Peppering / Pepper Spots
Very small dark specks visible in an intensifier image. They are commonly associated with minor cosmetic characteristics of the tube.
Phosphor
Material on the output screen of an image intensifier that converts electrons back into visible light, creating the image you see.
White Phosphor
An image intensifier output that appears primarily in grayscale rather than the traditional green image.
Good to know // White phosphor describes the output image color—not the generation or overall performance level of the tube.Green Phosphor
The traditional green monochrome output associated with many image intensifier tubes.
Photocathode
The light-sensitive layer at the input side of an image intensifier. It converts incoming photons of light into electrons.
Think of it as // The first step in converting a dark scene into an intensified image.Photocathode Sensitivity
A measurement of how effectively the photocathode responds to incoming light and produces an electrical signal.
Resolution
The ability of the intensifier or complete system to reproduce fine detail. Tube resolution is commonly expressed in line pairs per millimeter (lp/mm).
Remember // Resolution matters, but it should not be evaluated by itself when comparing tubes.Scintillation
The grainy, sparkling, or "snowy" electronic noise visible in an intensified image, especially when available light is extremely low.
Plain English // The darker it gets, the more visual noise you may notice.Signal-to-Noise Ratio (SNR)
A measurement comparing useful image information—the signal—to electronic noise generated by the intensifier. Higher SNR generally means a cleaner, more usable image as available light decreases.
Remember // Higher is better. SNR is one of the most useful specifications when comparing intensifier performance.System Gain
The effective light amplification of the complete night vision system after losses from optics and other components are taken into account.
Thermal Imaging
Imaging technology that detects emitted thermal energy rather than amplifying available visible and near-infrared light.
Important // Thermal and image-intensified night vision are different technologies with different strengths.Tube
Common shorthand for the image intensifier tube inside an analog night vision device.
White Phosphor (WP)
Common shorthand for an image intensifier with a grayscale or white phosphor output.
White Boxing
A process involving operating an intensifier while viewing a uniformly illuminated surface. It is sometimes discussed as an attempt to reduce certain image artifacts.
Caution // This should not be treated as routine maintenance or a universal repair method.Zones 1 / 2 / 3
A way of describing where cosmetic spots or imperfections are located within the circular image produced by an intensifier tube.
Easy way to remember // Zone 1 is the center. Zone 2 surrounds it. Zone 3 is toward the outside edge.NEXT STEP // GO DEEPER
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