Night Vision Terminology/Glossary

This articles explains the common terminology that are used in the night vision world.

 

Automatic Brightness Control (ABC)
This feature automatically adjusts the voltage to the microchannel plate, ensuring the image intensifier maintains optimal brightness and protects the tube. It’s particularly noticeable when transitioning from dark to bright environments, where the image briefly brightens before stabilizing at a consistent level.

Auto-Gated Power Supply
Auto-Gating shortens the cathode voltage’s duty cycle by rapidly toggling it on and off. This proprietary method maintains high resolution and MTF (Modulation Transfer Function) while reducing strain on the tube under bright conditions. It works by lowering the average current from the photocathode, enhancing image quality in dynamic lighting scenarios like urban operations.

Black Spots / Peppering
These are minor imperfections in the image intensifier or debris between lenses. They don’t impact performance and are a natural result of manufacturing. Each tube has unique spots.

Blemmish

Black spot that are big enough that impairing visions, these could cause by manufacture process or exposure to highlight damage. 

 

Bright Spots
Caused by flaws in the microchannel plate’s film, these are small, flickering, or constant bright areas. They typically disappear when light is blocked. To test, cover the lens; if the spot remains, it’s an emission point requiring inspection.

Bi-ocular
Viewing a single image source with both eyes, like watching TV.

Binocular
Using two separate channels (one per eye) for depth perception and improved situational awareness.

Blooming
Overloading of the intensifier tube by bright light, causing parts or all of the image to whiten. Common in Gen 0 and 1 devices, it creates a “halo” effect around light sources.

Bright-Source Protection (BSP)
An electronic function that lowers photocathode voltage when exposed to bright lights, protecting the tube but potentially reducing resolution temporarily.

Boresighting
Aligning a weapon-mounted device with the weapon’s bore. See also: Zeroing. For Night Vision it means to adjust the monocular to your natural axis as close as possible. 

Collimation
Aligning the internal optical axes of a system.

Convergence
The inward movement of the eyes to focus on nearby objects.

Chicken Wire / Honeycomb
A pattern of hexagons or squares dark lines in the field of view, visible during highlight conditions. 

Daylight Lens Cover / Daytime Filter
A cap with a pinhole for limited light entry, used for training but not extended periods.

Daylight Training Filter
A glass filter that reduces light to safe levels for daytime training.

Demist Shield
A filter preventing dust, dirt and condensation on optics during temperature changes or prolonged use.

Diopter
A unit measuring lens refractive power or eye correction, typically adjustable from +2 to -6.

Equivalent Background Illumination (EBI)
The faint glow in an image intensifier when no light is present, affected by temperature. Lower EBI values indicate better performance.

Edge Glow
A bright or sparkling defect in the outer viewing area.

Electronic Noise (Scintillation)
A random sparkling effect in the image, common in low-light conditions.

Emission Point
A steady or flickering bright spot in the image that doesn’t disappear when light is blocked. If persistent, it requires repair.

Eye Relief
The optimal distance between the eye and the eyepiece for clear viewing.

Field-of-View (FOV)
The visible area through the intensifier, measured laterally and vertically.

Figure of Merit (FOM)
A performance metric for image intensifiers, calculated as resolution (lp/mm) multiplied by signal-to-noise ratio (SNR). Higher FOM indicates better performance.

Gain
The amplification of light by the image intensifier, measured as tube gain or system gain. System gain is more relevant to users.

Gallium Arsenide (GaAs)
The semiconductor material used in Gen 3 photocathodes, sensitive to visible and near-infrared light.

Generations in Night Vision
Image intensifiers are categorized by generations (GEN), each representing advancements in technology. Gen 3, with GaAs photocathodes, offers superior sensitivity. Gen 4 is often a marketing term for high-end Gen 3 devices. Most modern Gen2 are comparable as Gen3, since they uses similar technology as Gen 3 but have different chemical components. 

Halo
A bright ring around light sources caused by electron collisions in the microchannel plate.

Interpupillary Distance (IPD)
The distance between the user’s pupils, typically 55 to 72mm for military personnel.

IR (Infrared) Illuminator
A built-in or external IR light source invisible to the naked eye but visible through night vision devices, allow users to read map and navigate in ultra dark environment.  

IR Range
The spectrum between 700 nanometers and 1 micrometer, invisible to humans.

IR Laser
High-power devices providing long-range illumination, often reaching thousands of meters.

ITAR (International Traffic in Arms Regulations)
U.S. regulations controlling the export of defense-related items, including night vision equipment.

Lp/mm (Line Pairs per Millimeter)
A measure of image intensifier resolution, with higher values indicating better clarity.

Monocular
A single-channel optical device.

NATO-STANAG
Standardized agreements for NATO equipment.

mA/W (Milliamperes per Watt)
A measure of photocathode sensitivity to light.

Magnification
The lens’s power to enlarge an image, e.g., 4X makes objects appear four times larger.

Microchannel Plate (MCP)
A component in Gen 2 and Gen 3 systems that multiplies electrons, improving resolution.

Mil-Dots
A reticle system for range estimation and target leading, based on milliradians.

MILSPEC
Military specifications ensuring products meet defense standards.

Minute of Angle (MOA)
A unit for measuring angular adjustments in shooting, equivalent to 1.047 inches at 100 yards.

Near-Infrared (Near-IR)
The shortest infrared wavelengths, from 750 to 2,500 nanometers.

National Stock Number (NSN)
A 13-digit code identifying standardized military supplies.

Phosphor Screen
Converts electrons into visible light in the image intensifier.

Photocathode
The input surface that converts light into electrons, key to intensifier performance.

Photocathode Sensitivity
A measure of how efficiently the photocathode converts light into electrons.

Picatinny Rail / Mount
A standardized mounting system for weapon accessories.

Resolution
The ability to distinguish between close objects, measured in lp/mm for intensifiers and cycles/milliradian for systems.

Reticle
An aiming point or pattern within an optical sight.

Sacrificial Window
A protective glass filter for the objective lens.

Signal-to-Noise Ratio (SNR)
A measure of image clarity, with higher SNR indicating better low-light performance.

• Signal: True light captured by the photocathode.

• Noise: Scintillation or sparkle effect in the tube.

• SNR: Ratio of signal to noise; higher SNR means better low-light performance.

• FOM: Calculated as Center Resolution × SNR, representing overall tube performance.

Variable (Manual) Gain Control
Allows users to adjust brightness manually, a feature found in devices like the PVS-14.

Weaver Mounting System
A weapon attachment system for sighting devices.

Zeroing
Aligning an aiming device with a weapon’s projectile trajectory.