The coolness factor of a pair of night vision goggles is high. There’s something primal about being able to see in the dark when our eyes haven’t evolved with that capacity. But how does it happen? It might seem like magic, but there’s some interesting science behind the technology. Night vision goggles use visible light, infrared, and digital technology to create the green image you see, and the technology is continuing to advance. Read on to learn exactly how humans have managed to bring light to the night.
Infrared is light, plain and simple. Our eyes only see light (which our brains interpret as color) within a narrow slice of the entire electromagnetic spectrum. Just outside our vision, right above the color red, is invisible infrared light. Because light sources are limited at night, night vision goggles use infrared light to help create an image.
Infrared isn’t the only light source gathered in night vision goggles. They pull in visible light, too, some of it almost undetectably faint, and some of it bright like moonlight and starlight. The goggles then amplify the light and infrared and interpret it electronically into a black and white image, which is then filtered to green in your eyepieces.
Electronic information only consists of on and off switches, or ones and zeroes. These polar opposites are most often interpreted as black and white since electrons don’t contain color. But the human eye is most sensitive to green light, so staring at green images for long periods of time is much easier on the eyes than black and white. This is also why computer screens used to primarily consist of green text on a black background. So, night vision goggles are engineered with green-hued screens to keep your eye strain at a minimum.
Here’s where it gets complicated. When all that faint light and infrared enters through the night vision goggle lenses, it hits a device called a photocathode. When the photocathode is illuminated, it releases electrons to a photomultiplier, a device that amplifies light. These electrons are then accelerated onto a fluorescent phosphor screen for your viewing pleasure. Most night vision goggles also contain an infrared spotlight mounted on top to help illuminate your subject and give your goggles more light waves to work with.
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You may have stumbled across the terms Gen1, Gen2, or Gen3 when looking at night vision products. These refer to the technology behind the night vision. Gen1 night vision uses an intensifier tube to accelerate electrons to the screen, while Gen2 uses a special plate that multiplies the electrons first. Gen 3 uses a more advanced photocathode to create more photoelectrons than either of the previous generations. While each of the models will give you night vision, you’ll get much clearer imagery with Gen2 or Gen3.
You’ve probably heard of thermal imaging in your quest to better understand night vision. Thermal uses infrared, as well, but instead of detecting light waves, it detects heat signatures. The device gathers heat patterns and creates a thermogram, or temperature pattern, which is then converted into electrical impulses. Finally, these are interpreted digitally and displayed by a screen. While thermal imaging can help you detect movement and living things in the dark, it is not the same thing as night vision.
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Night vision goggles can be exciting to use, but they’re also very useful for hunters, animal behaviorists studying nocturnal animals, bird watchers looking for those elusive night-dwellers, the military and police, and even for security. This fascinating technology has taken the human eye far into the future, beyond the capacity nature has given us.
Header image credit: Tech. Sgt. Robert Cloys
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