Glossary

This page contains a comprehensive collection of the terminology used around night vision.

Term(s)	Abbreviation(s)	Description
Image Intensifier Tube Image Intensifier	IIT I²	The core component of a night vision device. When focused, low light shines into it on one side, the phosphor screen on the other side will show an intensified image.
Signal-to-Noise Ratio	SNR	A number that indicates how good an image intensifier is at producing a clear (noise-free) image from a dark scene.
Resolution	Res.	A number that indicates how sharp the image produced by an image intensifier is.
Gain		A measurement of how bright the output image produced by an image intensifier is.
Fixed Gain		An image intensifier with fixed gain does not offer the user a method of gain adjustment.
External Gain Adjustment Circuit Manual Gain Variable Gain	EGAC	A component of some image intensifiers that allows the user to adjust the gain manually. Especially useful for monocular devices to allow reducing discomfort of only one eye being exposed to the bright output image.
Autogain		An image intensifier with autogain attempts to keep the output brightness constant throughout different lighting conditions. Modern image intensifiers both with fixed or with manual gain usually have some form of autogain. Thus, the term autogain is often used interchangably with fixed gain.
Gating Autogating	AG	Autogating is a method used by most modern image intensifiers to avoid overloading and as such damaging their internals when exposed to bright lights.
Chickenwire		Black straight lines that can form hexagonal or square patterns. Defect of the fiber optical output.
Fixed Pattern Noise	FPN	A hexagonal pattern made of black or white lines. Most Gen. 2 and Gen. 3 image intensifiers exhibit FPN in very high light and some also in low light. It is an artifact of how the MCP is constructed and no cause for worry.
Generation	Gen.	A number that denotes the technological generation of an image intensifier.
Date of Manufacture	DOM
Field of view	FOV	In night vision, FOV refers to how much of the user's field of vision is covered by the (usually circular) output image. Higher FOV requires less head movement to observe a scene.
Green Phosphor	GP	An image intensifier with green phosphor produces a monochrome green output image on the phosphor screen.
White Phosphor	WP	An image intensifier with green phosphor produces a monochrome white output image on the phosphor screen. Sometimes with a blueish or greenish tint, depending on the manufacturer.
Blemish	Blem	Completely dark areas of varying sizes and shapes in the output image where an image intensifier "burned out"., usually due to exposure to very bright light, e.g. lasers. Blemishes are permanent.
Burn-in Burn		Similar to blemishes, except that the areas aren't completely dark, but instead just less bright than the rest of the image, usually due to exposure to very bright light. Burn-ins are a precursor to blemishes, usually due to shorter or less intense exposure to the light source. Burn-ins can sometimes be partially or fully reverted by using blackboxing or whiteboxing.
Blackboxing		A method of stimulating the peculiar ”self-healing” process that some image intensifiers have been found to have, where the image intensifier is left running for extended periods of time in a completely dark enclosure.
Whiteboxing		Similar to blackboxing, except that the image intensifier is pointed at a uniformly bright surface, e.g. a wall lit up by a flashlight. Should be performed only as a last resort.
Emission Emission Point	EP	Permanent damage to an image intensifier manifesting itself in a single point or area in the image that is constantly bright. Emission points can get worse over time and thus image intensifiers with EPs should be avoided.
Ghosting		A temporary bright spot in the output image of an image intensifier caused by exposure to a very bright source which usually disappears after some minutes of operation. Ghosting is an indicator that prolonged or more severe exposure to the light source can lead to burn-in or blemishes.
Streaks		Dark or light streaks that form behind sources of light moving in the output image of an image intensifier. Only visible in some image intensifiers, they disappear very quickly. For many Gen. 3 image intensifiers they occur most easily during the first few minutes of operation. Autogating usually removes the streaks.
Scintillation		Bright spots which occur on the  image screen randomly in space and time.
Spot		A single black point in the output image, usually a defect introduced during manufacturing.
Peppering		Multiple tiny spots, can look like a darker cloudy area, usually a defect introduced during manufacturing.
Zone 1/2/3		A method to describe where on the output image an imperfection lies. Zone 1 is the inner 1/3 of the image, Zone 3 is only the outer edge of the image, and Zone 2 is the rest inbetween.
Going To Air		When there is a leak in the vacuum contained inside of the image intensifier a shadow will slowly start creeping into the output image of an image intensifier, either just from one side (like a waning moon) or from all sides. This process can be very fast or very slow. A tube that is "going to air" should be avoided, as it's irreversible and will mean total failure of the image intensifier at some point in the future.
Quantum efficiency	QE	Quantum efficiency is a unitless value, that states the incident photon to converted electron (IPCE). This measurement is usually given in %. The human eye, when adopted to the dark has a quantum efficiency of around 1-4%. [1][2] Various photocathodes have different quantum efficiencies, depending on the wavelength of the incoming light. S-1 photocathodes have a quantum efficiency of up to 1% in the UV range and up to 0.5% in the IR range.[3] S-20 photocathodes have a quantum efficiency of up to 24.5% in the UV spectrum and a quantum efficiency of up to 1.5% in the IR range. S25 photocathodes have a quantum efficiency of up to 16.5% in the UV spectrum and up to 12.5% in the IR range (that being said the S-25's response range ranges farther into the IR range than the S-20).[4][5]