Night vision goggles project green images because the human eye can see them better.
Night vision goggles can seem somewhat magical. Put them on in pitch darkness, and suddenly, you can see. A device that would allow soldiers to see at night was an elusive concept until the first generation of night vision instruments was introduced during the Korean War. These nifty tools transformed infrared to visible light, but they had a major drawback: they needed to shine infrared or filtered lights in order to work. This made the people using them an easy target for anyone who had the same technology. Second generation goggles could pick up low levels of infrared light that are emitted by all living plants and animals. The goggles in use today simply amplify low levels of naturally-available light, relying on a few crucial components.
Photocathode
The photocathode is located behind the lens in third-generation night vision devices. The lens focuses available light, or photons, onto the photocathode. The energy from the light causes the photons to release electrons, which are then passed through an electric field that increases their speed. The electrons then pass through a disk called the microchannel plate.
Microchannel Plate
A microchannel plate (MCP) is made up of millions of tiny conductive glass fibers, fused together in a honeycomb of interconnected hexagons and sliced into a thin plate. Each glass fiber, or capillary, can multiply the electrons that are directed onto the plate by the photocathode. These disks are used in all sorts imaging devices used in medicine, science and the military, including x-ray machines, microscopes and, of course, night vision goggles. In night vision goggles, the MCP basically creates a denser cloud of electrons, which the eye detects as a clearer version of the original image.
Phosphor Screen
Finally, the multiplied electrons pass through a piece called the phosphor screen, which converts them back into photons. The energy of the electrons basically makes the phosphor glow, rendering the original image back into visible light. The reason most night-vision goggles project images in an acid green color is because of the green phosphor used in this part of the device. The color green is a conscious choice: the human eye can detect more variations in shades of green than other colors, allowing users to pick up on more details in the image they ultimately see through the eye-piece of a pair of night vision goggles.
Tags: night vision, vision goggles, back into, electrons which, goggles project, microchannel plate
