Ask Smithsonian: How Does Night Vision Work?

The ability to see in the dark is becoming more accurate and more portable

Night vision technology, which was once quite clunky, has become so lightweight and powerful that it is shifting the battle paradigm for U.S. forces. Night has become day.

The ability to use a scope to see at night was first developed in the 1930s by the German military, but American forces soon followed suit. Now, night vision technology is considered an essential tool in a soldier or airman’s gear, allowing them to move safely without fear of surprise attack and to seek out targets in almost total darkness or through thick curtains of smoke, fog and dust during the day.

“It improves their mobility, their survivability and their lethality,” says Lt. Col. Timothy Fuller, product manager for soldier maneuver sensors at the U.S. Army’s Program Executive Office Soldier (PEO Soldier), a research and development facility, based in Ft. Belvoir, Virginia.

Night vision scopes and goggles are being used around the clock now, says Fuller.

The technology didn’t really take off until the late 1950s when the PEO Soldier had a simple, but not-so-easy goal: the “conquest of darkness,” according to an Army history.

There are two ways to augment what a human can see in darkness or other obscured conditions: image enhancement (traditionally thought of as night vision) and thermal imaging.

With image enhancement, a scope uses a lens to capture light reflected from the moon or stars and passes it through an image-intensifier tube. Within that tube is a photocathode which when hit by light energy, or photons, emits electrons.

Coated with a photosensitive compound inside, the tube quickly turns a single electron into many thousands in a cascading effect.

At the end of the tube, the electrons hit a screen coated with light-emitting chemicals called phosphors. These phosphors convert electrons back into photons, creating an image on the screen—usually green, as humans are thought to process the image best with that color. An ocular lens allows the user to magnify and focus the image.

The concept of accelerating electrons to hit a phosphor screen, which creates a glow, works on the same principle as old televisions and computers that operated with cathode ray tubes, says Tom Bowman, division director of ground combat systems at the U.S. Army’s Night Vision and Electronic Sensors Directorate.

Thermal imaging devices use a sensor called a microbalometer to read the difference in temperature between an object and its environment, creating an image of the object. The data from the microbalometer is sent to a display, so the user can then see the object. Thermal imaging can sense the heat being radiated off any object—whether it is a rock, a truck, a building or a human being, says Bowman. The image produced is similar to the one on a black-and-white television set. 

Frequently, a thermal imager is coupled with image enhancement technology. “When we have total darkness, the thermal channel assists,” says Fuller.

The original first-generation night vision devices were used beginning in World War II and through the start of the Vietnam War. The first practical night vision device for foot soldiers was the Starlight Scope, introduced in 1964 and used by infantry during the Vietnam conflict. The six-pound, lengthy (at about 18 inches) device—which used a military-specific, bulky, expensive battery—did not exactly make for a light load.

Much of the progress in night vision technology over the past 50 years has been in creating more portable and lighter equipment, although visual acuity has also been improved. The so-called second-generation technology gave soldiers 20/50 vision. That has been improved with the current third-generation technology to 20/20, which means soldiers can see as well at night as they do during the day, says Bowman.

Scopes mounted on tops of weapons like rifles have shrunk from eight pounds each to around a pound, says Bowman.

Goggles were introduced to the field in 1977. The image intensification has grown greatly since then, and the latest technology combines night vision and thermal imaging in a headset that weighs about a pound—including the battery pack that straps to the back of the helmet and encases four AA batteries (allowing for almost 8 hours of use). In the 1970s, soldiers using goggles could detect a human figure from 500 feet away; now they can see about 1,000 feet into the dark.

These days, there are night vision baby monitors, binoculars, hunting scopes and surveillance cameras. 

But the average citizen can’t purchase anything equipped with the most recent advances. “You’re not buying a military piece of gear,” says Bowman. He says what’s available “is something akin to what we would have fielded back in the '70s.”

And the latest technology is closely guarded. “The Army is vigilant, to put it mildly,” about inventory control, says Fuller.

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