A night vision device (NVD) is anoptoelectronic device that allows images to be produced in levels of light approaching total darkness. The image may be a conversion to visible light of both visible light and near-infrared, while by convention detection of thermal infrared is denotedthermal imaging. The image produced is typically monochrome, e.g. shades of green. NVDs are most often used by the military andlaw enforcement agencies, but are available to civilian users. The term usually refers to a complete unit, including an image intensifiertube, a protective and generally water-resistant housing, and some type of mounting system. Many NVDs also include optical components such as a sacrificial lens,or telescopic lenses or mirrors. An NVD may have an IR illuminator, making it an active as opposed to passive night vision device.
Night vision devices were first used in World War II, and came into wide use during theVietnam War. The technology has evolved greatly since their introduction, leading to several “generations” of night vision equipment with performance increasing and price decreasing. Consequently, they are available for a wide range of applications, e.g. for gunners, drivers and aviators. Another term is “night optical/observation device” or NOD.