"NVDs [night vision devices] use image intensification technology to provide imaging in poorly lit situations, permitting navigation of terrain and recognition of objects and people that would normally be unrecognizable to the unaided human eye. These devices are widely used by emergency responders during nighttime surveillance, search and rescue, and covert operations. A key component of an NVD is the image intensifier tube, which may use a green or white phosphorous output screen. A green phosphorous output screen produces images in shades of green (green and black), while a white phosphorous output screen produces grayscale (black and white) images."
Department of Homeland Security: https://www.dhs.gov/