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How Does Night Vision Work?

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Channel: BrainStuff - HowStuffWorks
Categories: Science   |   Technology  
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Sure, night vision looks cool in the movies - but what is it, exactly? How can a scope or a pair of goggles help you see in near-absolute darkness?

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So night vision seems like a pretty cool idea, right? I mean, you see it all the time in movies. Some secret agent-type straps on a pair of goggles, sneaks onto a luxurious supervillain compound and mows down enemies under the cover of darkness.

Or the Predator stalks Arnold Schwarzenegger, killing his platoon one, by one, by one… And as you’re watching all this, you may occasionally ask yourself “Hey, do those goofy-looking goggles really work?”

The answer is yes. Absolutely. With a good night vision device, or NVD, you can see a person standing over 200 yards (183 m) away on a moonless, cloudy night.

And whether we’re talking goggles, scopes or cameras, most of these devices rely on one of two types of night vision: image enhancement (that’s the green-looking one) and thermal imaging, which is the bluish-gray stuff. They both produce results, but work in different ways.

Thermal imaging captures the upper portion of the infrared light spectrum. Objects emit this as heat rather than reflecting it as light. Hotter objects – such as the bodies of secret agents – emit more of this light than cooler objects, like buildings, trees or, you know, dead bodies. And that’s what you’re seeing when you use thermal imaging, essentially. A measure of temperature from -4 degrees Farenheit to 3,600 F.

The magic (well, you know, science) starts at the lens, which focuses the infrared light emitted by all of the objects in view and uses a phased array of infrared-detector elements to create a temperature pattern called a thermogram, which is translated first into electric impulses, and then into data for the display, where it appears as various colors depending on the intensity of the infrared.

Then there’s image enhancement. This collects tiny amounts of light, including the lower portion of the infrared light spectrum, and amplifies it.

Image enhancers use a photocathode to convert photons into electrons, and high voltage to amplify those electrons in a microchannel plate, or MCP, before they hit a screen coated with phosophors.

Here’s the crazy part – these electrons maintain their position in relation to the microchannel they passed through, which provides a perfect image since the electrons stay in the same alignment as the original photons. When they hit the screen, their energy excites the phosphors, releasing photons. Those phosphors create the green image you see when you look through a night vision scope.

Night vision devices have been around for more than 40 years, and they’ve gone through multiple improvements. Today they’re used for everything from military applications to navigation and wildlife observation.


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