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   Night Vision Dictionary

EPM Gen3

Automatic Brightness Control
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.

Black Spots
Usually cosmetic blemishes in the image which are inherent in the production process. In other cases, as dirt builds on the lens, black spots are also visible. Black spots resulting from the production process neither influence the image quality nor interfere with night observation. Spots which form due to dirt should be removed carefully with a soft cloth.

Bright-Source Protection
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 unit of measure used to define eye correction or the refractive power of a lens. In most cases, an optical eyepiece will accommodate for differences in individual eyesight among users.

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.

Edge Glow
There is a defect in the image area of the NVG. Edge glowis a bright area (sometimes sparkling) in the outer portion of the viewing area.

Electro-optical transducer
Primary system which directs and accelerates the photoelectronic flux taking into account the potential difference between the photocathode and the screen, and forms the electronic image.

Emission Point
A pinpoint of bright light in the image area that does not vanish when all light is blocked from the objective lens.

Eye Relief
The distance your eyes must be from the farthest element of an eyepiece in order to achieve the optimal image area.

Sometimes referred to as brightness gain. Gain is the number of times a night vision device amplifies light input. For a detailed description of gain and how it can affect performance, please refer to our “First Time Buyer Section”.

Generation 2
Most advanced standard of night vision technology. Uses Image Intensifier Tube with Micro channel Plate for a crystal clear and fine detail image.

Light radiated with wavelengths longer than those of red light.

Line Pairs per Millimeter (lp/mm)
Units used to measure image intensifier resolution.

The unit denoting the photons perceivable by the human eye per one second.

Objective Lens
Collects all available light and focuses it on the image intensifier. It also provides image magnification. The best objective lenses have low magnification (5x or less), are high-speed (f2 or faster) and are coated for maximum efficiency in the near-infrared bandwidth.

Phosphor Screen
Positioned at the back of the intensifier tube, the green phosphor screen renders a visible night vision image. The human eye is most sensitive to green contrasts.

Converts light (photon energy) into electrons (electrical energy) which are then amplified in the intensifier. The objective lens focuses available light on the photo-electric surface of the photocathode which is excited and passes electrons within the tube.

The ability of the photocathode material to produce an electrical response when subjected to photons.

The “red colored” round aiming device found in many night vision rifle scopes which serves as cross-hairs.

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). For a detailed description of resolution and how it can affect performance, please refer to our “First Time Buyer Section”.