Humans cannot see in the dark, yet millions of television viewers regularly saw green, ghostlike tanks, soldiers and reporters negotiate the desert blackness during the recent Iraq war. Night vision tubes built into video cameras made it possible--the same technology that outdoor enthusiasts use to spot nocturnal animals or buoys on midnight waters and that police use to observe crooks in shrouded doorways.
No matter how dark the night, the stars, moon and man-made fixtures supply a small number of photons that such instruments can detect. The gear, which was invented during World War II by the military and has since trickled down to consumers, has advanced in "generations": rough standards of effectiveness defined by the U.S. Army Night Vision Labs at Fort Belvoir, Va. By the late 1980s, generations one and two gave way to the prevailing "Gen 3" products. Under a quarter moon (0.01 lux of light), they can distinguish a six-foot-tall person at 600 yards; quality monoculars cost $2,000 to $3,500.
This article was originally published with the title Seeing Green.