Night vision technology is not just for movies, but they have a ton of uses in the military and civilian sectors. It is well integrated into goggles, scopes, and cameras, and they provide us with the ability to view things in darkness. When people first think about night vision goggles, the color green pops instantly in their mind.
Why are night vision goggles green? Why can’t these goggles be blue, yellow, or even black and white? There is actually a good reason why these night vision devices are green. Before we talk about that, though, let us look at what night vision exactly is and some general information about it to help you understand it better.
To give the simplest definition, night vision is basically the ability to see things through a device even when it is dark. Even in darkness, there is some sort of light, but it may not be visible to the human eyes. This kind of light is of two types: ultraviolet light which ranges between 100 nm and 400 nm, and infrared light which ranges between 700 nm and above.
The light visible to the human eyes is between 400 nm and 700 nm. For us humans to view ultraviolet light and infrared light, we need an external device that will detect this light correctly and will amplify it to the point where it makes everything in the surrounding visible to us. This is where night vision devices come in use.
The very first generation of the night vision device was developed by the US and German Military somewhere in the mid-1930s. Infantry and tanks used these devices during World War II. Back then, these night vision devices required a significantly large power supply that needed to be carried around by the soldiers and these worked on an image intensification technology.
With technology on these devices advancing further over the decades that followed, night vision devices have become more sophisticated. While it still uses image intensification technology, they have now become smaller that you can wear it on your head. At this point, they were used for the first time by the US Military in the Vietnam War.
At present day, the second-generation night vision devices are widely available for civilian use. But the technology meant for police forces and the military is definitely upgraded. Even with all the technological advances in night vision devices, they work on the very same principle of image intensification as it did in the early 20th century.
The night vision goggles work by letting the dim light in a dark surrounding enter into the lens that is at the front. They are made of photons of different colors.
When they enter into the goggles, they strike a surface that is light-sensitive, which is known as the photocathode. This is very similar to a solar panel which is more precise, and its job is to turn photons into electrons.
These electrons then get amplified by a photoelectric cell called a photomultiplier. Each one of these electrons that enters the photomultiplier will result in several more of it leaving.
Once they leave, they hit a phosphor screen, which is quite similar to an old TV. As the electrons hit this screen, it creates tiny flashes of light. Now that there are more photons in comparison to how many entered earlier, the screen will make a significantly brighter version of the original scene.
Let’s begin by clarifying this first. Not all night vision goggles are green; you will find several different colors available these days. That being said, night vision goggles with green color are always considered to function the best, which was discovered since night vision goggle makers have tried out multiple colors.
They have found that the multiple shades which are capable of making up the monochrome night vision images are actually perceived to be the most accurate when they are green in color. The next best color is white screens.
Even in darkness, when the photons hit and enter the lens of the night vision goggles, they carry the light of all possible colors. However, when the photon gets converted into electrons, there isn’t any way to preserve that information.
What happens is that the incoming colored light gets converted into black and white. We are sure you are wondering why these goggles don’t look black and white then.
The reason why it doesn’t appear so is that the phosphors on their screen are chosen deliberately to make these pictures green as human eyes are more sensitive to light in this color, especially since it is near the 555nm wavelength. Additionally, it’s also quite easy to see green screens for a long time in comparison to a black-and-white screen.
They are also excellent at conserving battery power. This is also why computer screens a long time ago used to be green.
So, by now you have figured that night vision goggles are also referred to as image intensifiers. That is because they can locate the dimmest of dimmest light in the surrounding and then intensify that light to make you view in darkness.
At times where there is just not enough light, though, these night vision goggles are simply useless. To give you an example, if a firefighter is inside a smoke-filled building trying to find whether anyone’s trapped inside or not, the goggles are as useless as your eyes.
That is where thermal imaging devices come in great use. The way this works is by looking for heat instead of light. All living beings and many forms of equipment generate heat, and this becomes easy for a thermal imaging device to pick up. Hence, there is often a debate which one between night vision and thermal imaging devices are better.
We hope now you know the exact reason why are night vision goggles green. In a nutshell, the green color offers the best result in low light compared to other colors. Similarly, they are easy on the eyes, and you can view things longer.