Night vision goggles
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Night vision goggles (NVG) are a type of optical instrument that allows one to see in the dark. They are most often used by the military.
There are two common types of night vision goggles:
- Passive night vision goggles — these pick up any light in the given area and amplify it several thousand times using an image intensifier. This works by the photoelectric effect. As a photon collides with a detector plate, the metal ejects several electrons that are then amplified into a cascade of electrons that light up a phosphor screen. Often a dim star in the sky is enough to illuminate an entire field. This type is commonly used for war reporting, tinting the picture green. The color green is chosen because the human eye is most sensitive and able to discern the most shades in green.
- Active night vision goggles — these project infrared light (the same type used by a remote control), and produce an image from the light reflected back. These goggles may require an image enhancer to amplify the light. This feature is commonly found on home video cameras, as it suits most consumers' needs for seeing in the dark. Pointing a television remote control at this type of system produces a glaringly bright image.
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