Whether in the movies or on television shows or even in cartoons, we have definitely seen quite a number of spies or soldiers using special glasses that allow them to see in low-light settings. Famously known as night vision devices, they always made us curious regarding its authenticity. But, is it really true? If yes, how do night vision goggles work? Is there some sorcery involved?
If you are questioning whether these special glasses are just the stuff of the fiction world, then you are not alone. Night vision goggles really do exist, and they do work. In fact, some of the best night vision devices will allow you to see a person or an object that is placed more than 200 yards away even on a rather dark night.
There are two different kinds of night vision goggles that are available on the market. The first kind works in a manner such that it relies on the temperature difference between the object and the surrounding environment.
This is often called the Forward-Looking Infrared (FLIR). You will find these installed on combat aircraft. The other kind of night vision device relies on light amplification. In order to work on light amplification, the device must find and rely on at least a small presence of light somewhere in that space.
The ones that are referred to as night vision goggles are the most common example of night vision devices. These are also the kinds that are very commonly used.
Night vision goggles are one type of an electro-optical device. As mentioned earlier, these goggles amplify existing light in the surrounding rather than using their own source of light. In open areas, you will find the ambient light like the light from the stars and the moon.
The goggles capture this light using an image intensifier and electronic means. This light is further intensified thousands of times in order to create an image. This image is then displayed on to a phosphor display.
Through the objective lens of the night visions goggles, the ambient light travels through, and there it encounters a photocathode. This cathode is driven by a very high energy charge. This charged energy light then speeds across the vacuum, which is situated inside the intensifier.
The intensifier is where it comes in contact with the phosphor screen and produces a focused image. This image further becomes magnified by the eyepiece.
Inside the night vision goggles present is a phosphor screen. This screen is designed to be green in color intentionally. Even in the dark, all the photons that the night vision goggle’s lens hit are placed at the front and carry the light of different colors.
However, when these photons get converted into electrons, there is no exact way that can preserve the information. The colored light incoming is effectively black and white in color. So, the next obvious question would be that why don’t the images in the night vision goggles appear black and white?
This is because of the green-colored phosphor screen that is placed inside the goggles. As mentioned earlier, the color green is chosen intentionally. This is because our eyes are far more sensitive to the green-colored light.
Furthermore, it is relatively easier to look at a green-colored screen for a long period instead of looking at a screen that is in black and white. This is also exactly why computer screens back in the day were green in color. Hence, every single night vision goggles have their own eerie green glow.
As mentioned earlier, the way night vision goggles, also known as image intensifiers, work is by finding any small source of light and boosting the color that allows us to see in the dark. However, there are times when there would just not be enough light in that space. In such a case, the night vision goggles won’t work at all.
To give an example, if you are a firefighter who is trying to look if there is anybody trapped in a building filled with smoke, using night vision goggles will be equally useless as you looking through your eyes. In such cases, the best alternative is using thermal imaging goggles. These rely on heat instead of light, which will always give you some sort of picture even in darkness.
As you can see, there is no elaborate science behind how do night vision goggles work. In a nutshell, night vision goggles work on the smallest source of light, and if there is absolutely none of it, these goggles will not work at all. In such a situation, consider using a pair of thermal imaging goggles instead.