Even when a night appears completely dark, near-infrared light is emitted by the moon and stars. A night vision device amplifies this light to visible levels. The light, which is made up of photons, is converted into electrical energy and then accelerated through a thin disk called a microchannel plate. As the converted photons strike a phosphorus screen as electrons, they are perceived through an eyepiece in shades of green.
"The reason it's in green is because when you put the unit down, you want your eyes to remain dilated so you can see in dim light," said Rich Urich, director of operations at Night Vision Equipment Company in Prescott Valley, Ariz. "Use most any other color and your pupils will constrict when you take off the unit."
Infrared technology measures fraction of a degree differences of heat given off by objects. All living things and many objects — people, animals, recently used cars — emit heat in the form of infrared radiation. Infrared radiation is a part of the electromagnetic spectrum just below ("infra") the frequency of red light. Infrared devices read heat by absorbing infrared light, converting it into a grid of video signals and creating a picture the viewer can see.
Effective in Winter
Urich explains, while viewing through an infrared device: "you'll see varying shades of gray or black, with the whitest segments representing those giving off the most heat." Some reports have suggested that infrared technology will become more effective as winter arrives in Afghanistan, since contrasts between body temperatures and the external temperatures will increase. But Urich claims the contrast doesn't necessarily enhance infrared images, and once snow falls, the opposite is true.
"Infrared systems are very sensitive to white," he says. "The images can be compromised if there is snow everywhere."
Infrared devices might not only prove useful to ground troops and pilots for vision, they can also help detect recent footprints or tire tracks that could still be emitting heat. Even objects that have recently been touched, like a desk or door, can show traces of the recent activity.
Besides military use, infrared technology has proven useful in many other applications. Law enforcement use it to detect criminals operating at night, border patrol use it to monitor for illegal crossings, ranchers use it to hunt nocturnal predators such as coyotes and drivers in some specially-outfitted automobiles use it for better vision during night driving. The technology can also help create a thermal image of a home to find leaks and improve insulation.