A Peek at the Science Behind Night Vision

A 34-year-old San Francisco hiker is alive today thanks to night vision, CBS reports. The hiker was climbing up rocks near Muscle Beach near dusk when he slipped and fell 300 feet to the beach below. He lay there with leg injuries as the tide closed in on him. Night had fallen and ocean water surrounded him by the time rescuers arrived. Fortunately, the helicopter rescue team was able to spot him using night vision. He was assessed for injuries by a paramedic and flown to a landing zone for transfer to an ambulance. He is expected to fully recover.

Dramatic applications of night vision of this are made possible by the scientific advances that underlie this fascinating technology. Here’s a peek at the science of how night vision works and how recent advances are enabling amazing new applications of this high-tech surveillance tool.

How Infrared Light Enables Night Vision

There are a variety of different types of night vision that have advanced through several generations of technology. The story of night vision begins in 1929, when an early innovator in television design, Hungarian-born physicist Kálmán Tihanyi, sold the British government a method to improve anti-aircraft defense by applying infrared light. Infrared light is normally invisible because it has a longer wavelength than normal light, but Tihanyi figured out a way to convert it into a visible wavelength. Tihanyi’s innovation inspired the first version of night vision, known as Generation 0, which employed what is called active infrared or active night vision.

Generation 0 infrared works by throwing a beam of near-infrared light to illuminate an area, much like a flashlight. As the beam is reflected back, it hits a light-sensitive surface known as a photocathode, where the photons are converted into electrons by the photoelectric effect. A tube called a photomultiplier then intensifies electrons hitting the photocathode by using a series of electrodes to amplify them before they ultimately reach the last anode. There they strike a screen similar to a classic TV screen, called a phosphor screen, which transforms the electrons back into photons. This creates a final image which can be seen by the human eye.

Both the Axis and Allied powers used night vision devices during World War II. The Wehrmacht used an infrared spotlight called the Vampir to help aim assault rifles. U.S. soldiers used a night division aid called a sniperscope on M1 and M3 rifles. American forces also used sniperscopes in Korea.

From Active to Passive Night Vision

Generation 0 night vision devices suffered from a couple limitations. When electrons are accelerated, the resulting image is fuzzy and distorted. In addition to being hard to see, this tends to make device tubes wear out faster.

To address this issue, night vision developers introduced a new technology called passive infrared, which became Generation 1 of night vision. Passive infrared collects light from ambient sources such as moonlight or starlight. U.S. military forces began using Generation 1 night vision devices during the Vietnam War, adding scopes called Starlight scopes to M14 rifles and other weapons.

Passive infrared technology doesn’t work well under cloudy conditions or nights with no moon, and like active infrared, it produces pictures with limited clarity and suffers from short tube lifespans. In the 1970s, night vision developers discovered a way to make images brighter by using microchannel plates to increase the electrons entering image-intensifier tubes, creating Generation 2 night vision.

In the 1980s, night vision manufacturers significantly improved low-light visibility by using photocathodes made of gallium arsenide, which is exceptionally efficient at converting photons into electrons. Manufacturers also discovered how to make tubes last longer by coating microchannel plates with a barrier of ions. These innovations created Generation 3 night vision, which is still in use by military and law enforcement units today.

For the next generation of night vision, manufacturers are conducting tests with removing the Generation 3 ion barrier to allow amplification of more electrons in order to generate brighter pictures. They are also doing experiments with introducing a power supply gate that enables rapid adjustments to lighting conditions. So far, these changes have improved night vision performance, but have reversed the gains in tube lifespan made by Generation 3 devices. Generation 4 night vision remains a future achievement.

Seeing in Color at Night

The majority of commercial night vision cameras revert from color to black-and-white during conditions of low light. But in recent years, security provider Lorex introduced color night vision security cameras that can capture color even in low light. Color night vision cameras use especially powerful image sensors that are more sensitive to light. This enables the camera’s sensors to collect more visible light and create a color picture even when light conditions are very dim. This improves surveillance applications by empowering cameras to photograph identifying details such as eye color or clothing color that could not be photographed by traditional night vision cameras.

Seeing Heat With Thermographic Cameras

There are also thermographic night vision devices which do not depend on light at all but generate images by detecting heat signatures. Due to the black body radiation law, all physical masses give off radiation proportionate to their temperature. By applying this, cameras can sense differences in infrared radiation between objects and their environments and convert this data into visible images, known as thermograms. Thermographic cameras are already widely used for military and surveillance applications. Businesses and consumers are also beginning to use them. For instance, home inspectors can use thermographic cameras to detect problems with thermal insulation.