How Night Vision Equipment Works

The nuts and bolts of night vision

Night vision works by virtue of an image-intensification tube that amplifies small amounts of light. The light enters any given night vision device through an objective lens and then hits a photo cathode, which has a high-energy charge from a power source. The energy charge then accelerates across a vacuum in the intensifier and hits a phosphor screen, where the image becomes focused, magnified by the eyepiece. The phosphor screen of a night vision device is green because of the human eye's ability to recognize more shades of green than any other phosphor color.

The image-intensification process begins when the objective lens captures ambient light. The light then passes through the image-intensification tube to the photo cathode, which converts photons into electrons. While the electrons pass through the tube, similar electrons are released through the micro-channel plate. On the opposite side of the image-intensification tube, electrons hit the phosphor screen, creating the image that is seen through the objective lens. The green phosphor image can been seen through the ocular lens.

The image magnification of a night vision device can vary. The magnifying power of the objective lens and the strength of the image intensifier determine the distance at which a human being, or a figure the size of a human being, can be seen clearly in normal conditions. There are also limitations concerning distance that must be taken into consideration when looking at objects in darkness. Most night vision devices offer viewing capability ranging from 350 yards to 500 yards.