Night Vision Devices (NVD) is an optical instrument that allow images to be produced in levels of light approaching in total darkness.
Though these devices are often used by military and law enforcement agencies, there are available to civilian users as well.
Night vision devices were first used during the World War II. It was later then widely used during the Vietnam War.
The term for a complete unit of a night vision device are including an image intensifier tube, a protective and generally water-resistant housing, and some type of mounting system. The night vision devices also capable of working in 2 different ways, depending of their type.
Image enhancement - works by collecting the tiny amounts of light, including the lower portion of the infrared light spectrum, that are present but may be imperceptible to our eyes, and amplifying it to the point that we can easily observe the image.
Thermal imaging - operates by capturing the upper portion of the infrared light spectrum, which is emitted as heat by objects instead of simply reflect as light. Higher temperature objects such as warm bodies, emit more of this light than lower temperature objects such as trees or buildings.
It is said that, proper night vision equipment, can see a person standing over 200 yards (183 m) away on a moonless, cloudy night.
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