night vision device (NVD) is an optical instrument that allows images to be produced in levels of light approaching total darkness. They are primarily used by the military and law enforcement agencies, but are available to civilian users. The term usually refers to a complete unit, including an image intensifier tube, a protective and generally water-resistant housing, and some type of mounting system. Many NVDs also include sacrificial lenses, IR illuminators, and telescopic lenses.
Night vision devices were first used in World War II, and came into wide use during the Vietnam War. The technology has evolved significantly since their introduction, leading to several "generations" of night vision equipment with performance increasing and price decreasing. Another term is "night optical/observation device" (NOD).