If you have ever watched a movie in which night vision was used, or you have ever used a device that takes advantage of this technology to help people see in the dark, you have most probably noticed that the image shown through such devices is always green. The two come together so well that the moment someone mentions night vision binoculars to you, that instantly brings in front of your eyes that green image you are so familiar with.
The advantages of seeing what our eyes can’t see in the dark are tremendous. For military applications, as well as civilian operations, night vision technology offers tremendous benefits. It can help locate survivors of natural cataclysms, and it can pinpoint the location of an enemy. As a layman, you are, however, interested in learning why the image of this type of vision is green. Let’s make it all clear.
When was this technology invented?
You might be surprised to learn that this technology has been around for a while, being used extensively in World War II. Both the US military and the Reich, worked on this technology before and during the war, with the purpose of using it on the battlefield. Both the infantry and the tank divisions used it to identify the location of their enemies.
However, the night vision technology used more than half a century ago was nothing like the elegant portable night vision goggles we’re practically identifying it with. The devices used during those times were bulky and needed manpower to be transported and used in the field.
The idea of making this technology portable, as well as the possibilities, did not occur on a practical level until the Vietnam War when the US military began to use the first devices that could be worn by a soldier on his head.
The main principle that night vision goggles use remains the same: it is the use of whatever light is emitted by the surrounding environment, coupled with image intensification technologies. No matter how advanced night vision is today, you should remember that the same original idea that was used during the aforementioned conflicts continues to stay at its foundation.
So, what’s the idea with the green image?
To understand how the green vision occurs, we need to learn a bit more about all the technologies that are involved. These technologies are employed on goggles, as well as scopes and night vision cameras. They are essential for how the green image occurs, and we will approach them as follows.
This technology is capable of telling the heat signature of an object against the surrounding environment. In other words, it is capable of telling when the temperature of the target is different from the rest of the objects around.
While thermal imaging sounds something that is used in military-grade operations, illumination is pretty straightforward. The image intensification used by goggles, or other optical devices, might need more light input to process and render the image before your eyes when you look through them.
The illumination used is very close to the infrared band. By adding more light to the environment, the devices create better conditions for the night vision device to harness it and transform it into an image.
We have already mentioned it a few times, and now it’s the moment to reveal that this is the technology responsible for the green image you see through your night vision monocular, goggles, scope, or any other similar device, designed to offer you the ability to see in the dark.
How does image intensification create the image you see?
What happens when we look through any vision device is that the image intensification technology employed on the device takes the light emitted by the celestial bodies and multiplies it. That is why we can get a pretty good image of what surrounds us.
As you can guess by now, it is not possible for your goggles, monocular, or binoculars to work in pitch dark, but, the thing is, most of the time, you won’t need your device to perform in such a manner. Absolute darkness is difficult to achieve, so situations that would meet such conditions are extremely rare.
What about the green vision?
To get our explanation farther here is some more information that will help you understand how night vision devices work. When the photons from the light around hit the lens, they have all the colors. The thing is that the photons are turned into electrons, and then all the information which might relate to colors perceived by our eyes/brain turn only into black and white.
The explanation is that the image intensification element is made from phosphorus. As you may well know, phosphorus is green, and its luminance capability manages to capture the light from the surrounding environment and present it to you. Therefore, the image you will see is green, as well.
But why is phosphorus used?
It is not by accident that these devices use phosphorus. It all has to do with something called chromatic sensitivity. This ability is related to how sensitive the human eye is toward different colors. From the entire spectrum, the color green is the absolute winner, and that is why night vision goggles and other similar products are made with phosphorus.
To go even deeper, this chromatic sensitivity of the human eye toward the green color means that we perceive more shades of this color than of any other. What happens when our eyes can tell the differences between different values of green is that we can perceive shapes and objects.
Another advantage identified by specialists in this field is that we can tolerate looking at the green color for more extended periods of time than at any other color. The computer screens are green for this reason, as well.
And now you know why the night vision showed through various devices designed to help you see in the dark is green, and how that is beneficial for the human eye.