A
night vision device (
NVD) is an
optoelectronic 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 denoted
thermal imaging. The image produced is typically
monochrome, e.g. shades of green. NVDs are most often
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 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.