Night vision technology has dramatically improved in recent years, fueling strong demand for the latest innovations. The night vision device market, worth $5.07 billion in 2015, will expand at a compound annual growth rate of 8.8 percent to reach $7.73 billion by 2020, Markets and Markets projects. Underlying this growing demand is the fascinating science behind night vision. Here’s a closer look at how this technology works and how recent innovations have taken it to new levels.
Infrared Illumination Night Vision
There are several different types of night vision. The technology’s roots date back to 1929, when television technology pioneer Kálmán Tihanyi improved British anti-aircraft defenses by using infrared light. Infrared light has a longer wavelength than visible light, so it is normally invisible, but Tihanyi realized it could be converted into visible light. Tihanyi’s discovery spawned the earliest generation of night vision devices, known as Generation 0, active infrared, or active night vision devices.
Active infrared technology projects a flashlight-like beam of near-infrared light onto a target. When the beam bounces back, a light-sensitive surface called a photocathode uses the photoelectric effect to convert the photons into electrons. An image-intensifier tube, called a photomultiplier, uses a series of electrodes to amplify them before they reach a final anode. There they hit a phosphor screen, similar to an old-fashioned TV screen, which converts them back into photons, producing a visible image.
The German, Russian, and American military all used night vision devices during World War II, with the Wehrmacht introducing the Vampir infrared spotlight for the Sturmgewehr 44 assault rifle and the U.S. Army using the sniperscope for the M1 and M3. The U.S. Army continued using sniperscopes during the Korean War.
However, accelerating electrons produced distorted, fuzzy images, while also wearing out the lifespan of device tubes. Generation 1 night vision technology sought to improve this by introducing passive infrared technology, which collects ambient light such as starlight or moonlight. Passive infrared technology first saw military application during the Vietnam War, where Starlight scopes were used on weapons such as the M14.
Generation 1 night vision devices performed poorly on cloudy and moonless nights, and they continued to suffer from fuzzy pictures and short lifespans. Generation 2 devices, developed in the 1970s, improved low-light vision by adding microchannel plates that increased the number of electrons in image-intensifier tubes. This produced clearer, brighter images.
Generation 3 devices, developed in the 1980s and used by today’s military and elite law enforcement, dramatically improved ability to see in low-light conditions. Generation 3 photocathodes are made of gallium arsenide, which is highly efficient at converting photons into electrons, allowing for extremely low-light vision. Additionally, Generation 3 microchannel plates are coated with an ion barrier, extending tube lifespans.
Generation 4 devices are experimenting with removing this ion barrier to allow more electrons to reach the amplification stage to produce brighter images, while adding a gated power supply system that allows instantaneous adjustments to lighting changes. While improving performance, this limits the lifespan extension introduced in Generation 3, so Generation 4 devices remain in development.
Color Night Vision
Most commercial night vision security cameras shift from color to black-and-white in low-light conditions. However, innovative equipment manufacturers have developed color night vision security cameras that can detect color in low-light conditions. This is achieved by adding LED lights around the camera lens to illuminate the scene being filmed, then using high-powered image sensors to capture the reflected light. This allows the sensors to capture more visible light, producing a color image even in total darkness. This enables surveillance cameras to capture important details such as suspect hair and the color of their clothes that would be missed by most security equipment.
Thermal Night Vision
Finally, there are thermal night vision devices that do not require light at all, but instead detect heat. By the black body radiation law, all objects emit infrared radiation corresponding to their temperatures. This enables cameras to detect infrared radiation variations between objects and their surroundings and convert the information into a visible image called a thermogram. Thermographic cameras are traditionally popular for military and surveillance use, but are also increasingly used for commercial and consumer applications, such as detecting faulty thermal insulation.