How Night Vision Works

During the history of warfare, operations at night have always been degraded significantly, if not totally avoided. Typically, soldiers fighting at night have had to resort to artificial illumination, e.g., at first fire and later with light sources such as searchlights. The use of light sources on the battlefield had the detrimental result of giving away tactical positions and information about maneuvers. The advent of new technologies initially in the 1950’s and continuing into the present time has changed this situation. The engineers and scientists at the Night Vision & Electronic Sensors Directorate (NVESD) have discovered ways to capture available electro-magnetic radiation outside that portion of the spectrum visible to the human eye and have developed equipment to enable the American soldier to fight as well at night as during the day in order to “Own the Night”.

Image Intensification: Image intensifiers capture ambient light and amplify it thousands of times by electronic means to display the battlefield to a soldier via a phosphor display such as night vision goggles. This ambient light comes from the stars, moon or sky glow from distant manmade sources, such as cities. A soldier can conduct his combat missions without any active illumination sources using only image intensifiers. The main advantages of image intensifiers as night vision devices are their small size, light weight, low power requirements and low cost. These attributes have enabled image intensifier goggles for head-worn, individual soldier applications and resulted in hundreds of thousands of night vision goggles to be procured by the US Army. Research and development continues today on image intensifiers in the areas of longer wavelength spectral response, higher sensitivity, larger fields of view, increased resolution, advanced displays and image fusion.

Night Vision technology consists of two major types: image intensification (light amplification) and thermal imaging (infrared). Most consumer night vision products are light amplifying devices.

Light amplification technology takes the small amount of light, such as moonlight or starlight, that is in the surrounding area, and converts the light energy (scientists call it photons), into electrical energy (electrons). These electrons pass through a thin disk that’s about the size of a quarter and contains over 10 million channels. As the electrons travel through and strike the walls of the channels, thousands more electrons are released. These multiplied electrons then bounce off of a phosphor screen which converts the electrons back into photons and let you see an impressive nighttime view even when it’s really dark. All image intensified night vision products on the market today have one thing in common: they produce a green output image. In the night vision world there are generations that reflect the level of technology used. The higher the generation, the more sophisticated the night vision technology.

Generation 0 - The earliest (1950’s) night vision products were based on image conversion, rather than intensification. They required a source of invisible infrared (IR) light mounted on or near the device to illuminate the target area.

Generation 1 - The “starlight scopes” of the 1960’s (Vietnam Era) have three image intensifier tubes connected in a series. These systems are larger and heavier than Gen 2 and Gen 3. The Gen 1 image is clear at the center but may be distorted around the edges. (Low-cost Gen 1 imports are often mislabeled as a higher generation.

Generation 2 - The microchannel plate (MCP) electron multiplier prompted Gen 2 development in the 1970s. The “gain” provided by the MCP eliminated the need for back-to-back tubes - thereby improving size and image quality. The MCP enabled development of hand held and helmet mounted goggles.

Generation 3 - Two major advancements characterized development of Gen 3 in the late 1970s and early 1980s: the gallium arsenide (GaAs) photocathode and the ion-barrier film on the MCP. The GaAs photocathode enabled detection of objects at greater distances under much darker conditions. The ion-barrier film increased the operational life of the tube from 2000 hours (Gen 2) to 10,000 (Gen 3), as demonstrated by actual testing and not extrapolation.

Thermal Imaging:

Most objects in natural scenes, as well as human beings and manmade objects emit electro-magnetic radiation in the form of heat. Thermal imagers or infrared viewers (also known as FLIRs) gather the infrared radiation and form an electronic image for the soldier. Since they do not rely on reflected ambient light, thermal imagers are totally light-level independent. They also have significant penetration capabilities through obscurants such as fogs, hazes, and conventional battlefield smokes. There are two varieties of thermal imaging systems: cooled and uncooled. Cooled thermal imaging requires cryogenic cooling. Lower performing uncooled thermal imaging systems require no detector cooling but have sufficient performance to provide the low to medium performance required by individual soldier sights, infantry vehicles, navigation, robotics and missile seekers. Present research and development in cooled thermal imaging are pursuing multi-spectral imaging, improved sensitivity and resolution, and embedded signal processing to aid the soldier in target acquisition missions. Current uncooled research is directed at smaller size packages and power consumption with lower cost and increased sensitivity, resolution and field of view. Small, palm-sized uncooled thermal imagers are now available.