Last Updated on October 24, 2020
We’ve all seen those movies where the spec-ops soldier takes out a light source and then flips down his night vision goggles for a tactical advantage. While you might not be leading a ranger team into action, there’s no doubt about it — night vision goggles are pretty cool.
But just how do they work?
Without any visible light, night vision devices can help individuals see clearly in the dark for a number of different reasons. In this article, we’ll go over how night vision goggles gather “unseen” light, create usable imagery, the differences between night vision generation, and more!
It’s time to bring this topic to the light and find out exactly how night vision goggles work.
Before we can really explain how night vision goggles work, you need to have a basic understanding of the electromagnetic spectrum and the different forms of light found within, such as infrared light. That’s because night vision goggles can actually detect and use infrared.
But what exactly is infrared light?
Well, it turns out what light we can actually perceive is just a narrow slice of what is known as the electromagnetic spectrum. The electromagnetic spectrum is the entire range of different electromagnetic (EM) radiation that exists. And visible light is an EM wave that falls squarely in this range.
But there are many other forms of EM radiation and light that our eyes just cannot perceive on their own — such as infrared.
Do you remember the order in which a rainbow’s colors are set? It starts with red followed by orange, yellow, green, blue, and then violet. Well, it turns out that these colors are actually represented in that same order on the EM spectrum. And infrared literally means “before red”.
So, infrared light is light just below our eyes’ visible range. But just because we can detect infrared light with our own eyes doesn’t mean we don’t have the capability to put infrared to use. That’s exactly where night vision goggles come into play.
Night vision goggles work on the premise of amplifying the infrared light and other faint visible light around your target to electronically produce a clear usable image. We definitely want to be clear that some semblance of visible light must be present in order for night vision technology to actually work. But this can be moonlight, starlight, or other distantly produced light. There are only a few situations where you’ll have zero visible light to work with.
So, when a night vision device actually captures this faint and infrared light, it is directed to a photocathode. The photocathode is a very important part of the night vision assembly. It collects and converts the photons (light packets) into usable electrons.
After the electrons are created, they next head to the image intensifier tube — or IIT, a type of photo-multiplier. The IIT is what actually accelerates, amplifies, and converts the signal emitted from the electrons back into a usable image that you can see through the eyepiece.
So, what makes that trademark green output color? And why?
Well, when night vision imagery is originally produced, it’s only produced in black and white. There’s actually a special filter that your goggles will pass the light through in order to turn the image green.
Green is a very important color in terms of visible light. Remember the rainbow order from earlier? Green falls smack in the middle of our visible light spectrum making our eyes the most sensitive and receptive to that color. This means that we can look at green lighting for a longer period of time with minimal eye fatigue.
Another popular way of seeing images in the dark or other low light situations is through thermal imaging. And while these two serve a similar purpose, they operate on entirely different principles.
Night vision works by analyzing and converting faint and infrared light into usable images. However, thermal imaging is based on the natural heat emitted by people, objects, or others. These temperature differences are then collected and structured into a multi-colored heat map for you to see.
It’s not just military operators that can utilize night vision goggles. As a matter of fact, there are several different reasons why you may want to pick up a pair including:
Although night vision goggles can be very useful, you need to consider if you actually need them. Despite recent advances in their tech, the cost for these devices is still very high when compared to other standard optics.
However, if you need a pair of night vision goggles, we recommend starting off with a pair from Gen2. They’re the most cost-efficient for civilian use and will basically cover everything you need them to.
Header image credit: Tech. Sgt. Robert Cloys
Robert’s obsession with all things optical started early in life, when his optician father would bring home prototypes for Robert to play with. Nowadays, Robert is dedicated to helping others find the right optics for their needs. His hobbies include astronomy, astrophysics, and model building. Originally from Newark, NJ, he resides in Santa Fe, New Mexico, where the nighttime skies are filled with glittering stars.
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