We’ve all seen it: in the middle of our favorite action movie, our heroes dive into some remote jungle or desert for some nighttime reconnaissance. As they all suit up, they pull their night vision goggles down over their eyes. To fully immerse you in the experience, the movie’s director switches to a first-person view and lets you see through the eyes of one of the protagonists. Suddenly though, everything is green. Has this ever made you wonder, “why is night vision green?”
Maybe it’s a directorial decision? However, anyone who has ever served in the military can tell you that night vision is, in fact, definitely very green. So how does night vision work? Today, we’ll look at the science behind it and even look at why humans can’t see at night.
So you’re saying humans don’t have night vision?
I mean, we can sorta see in the dark, right? It might not be totally clear what we’re seeing, but we are generally able to make out broad-stroke details at night. We can see general shapes and maybe even up close details like a person’s face if there’s enough ambient light. Have you ever wondered how this happens?
First, the pupil of our eyes widens as light goes away. This widening allows our eyes to take in as much available light as possible. While it gives us some ability to see when it’s dark out, when you’re in a combat situation it’s not sufficient by any means.
So second, why don’t our eyes have natural green-tinted night vision? After all, animals like cats and owls can see just fine. Why can’t we?
Simply put, our rods and cones just aren’t made that way. Rewind all the way back to high school biology. Our eyes are made up of three parts: the aforementioned pupils, cones, and rods. Our pupils let the light in for the cones and rods to process.
The cones of our eyes help us see detail but need bright light to work. Because of this, at night our cones are basically useless. The rods of our eyes are more sensitive to low-light conditions, but primarily transmit the colors black and white to our brain. Effectively, the blue-like hue we see is a result of these two components working together as best as they can. As our pupils expand, our cones absorb more light. They then add whatever color and detail they can to the image sent to our brain by our rods.
So why is night vision green?
Before we answer that, let’s look at how night vision technology came about. In the 1930s, military scientists began developing night vision devices. While these were used in the 1940s during World War II, the technology at the time was bulky and power-hungry. These early generation units are the precursors to what we have today.
Gradually, we shifted towards more efficient forms of night vision technology. This next generation version of night vision is what soldiers used during the Vietnam War, and generally speaking, is what most consumers are able to currently purchase. While the military has improved its night vision tech, today we’ll be looking at the consumer-grade devices akin to what the military used in the 1970s in Vietnam.
Current night vision technology uses three different kinds of technology to produce the green hue we associate with night vision.
Night vision uses thermal imaging to look at temperature differences around an object. The warmer an object is, the brighter it’ll appear through night vision goggles. So the brighter green-saturated white areas you see in the movies (say, coming from the light of a nearby building)? That’s using thermal imaging.
The second technological component to night vision involves combining near infrared light with a nearby source of visible light. It works in conjunction with thermal imaging to produce the image.
This third and final piece is what gives us our green color. On a clear night, the moon and stars provide us with small but important sources of light. Night vision glasses use the photons from those light sources to magnify (read: intensify) the visible spectrum.
Together, these three pieces of tech produce green night vision. Okay, we’ve explained what tech makes it green. Let’s now look at why it’s green.
How does image intensification create green night vision?
Have you ever heard of phosphor? It’s a kind of material that uses “cold radiation” (not the dangerous kind of radiation!) to produce an illuminated image. Computer monitor manufacturers used phosphor in 1980s style displays, which is why everyone’s Oregon Trail game looked like it was designed by the Green Lantern. This is also the same reason radar screens from that same era (and even some today) look green. They use phosphor to produce the image.
The screen inside of night vision devices also uses phosphor. When the active illumination and thermal imaging tech absorb all of the available light, the image intensification components process this as green images.
But why green? Why not use red or blue phosphor, right? As it turns out, Mother Nature designed us to be most sensitive to green. Think about it practically. Have you ever tried to read red text on a black background? It’s almost impossible to make out. Now imagine red night vision on a field of black. It wouldn’t work!
The same thing is true for blue. Blue on black is hard to read, right? Imagine a combat situation with blue night vision on a black background. It’s going to be a pretty big fail.
Basically, we’re biologically wired to see green. We actually can see more shades of green than any other color. This is a process called chromaticity. When scientists mapped the chromaticity of the human eye, green had the highest score, which is why night vision is green.
So is green light good for sleep?
After all, if humans are most sensitive to green, does that mean it’s good for us? The answer a is huge, resounding no. We all know the problems with blue light, especially at night right before bed. This is why companies like Apple created “night shift” for their iDevices. They switch to yellow-hued tones at nighttime so the blue light from our LED screens doesn’t break our circadian rhythm.
Do you remember studying wavelength in high school physics class? Blue and green wavelengths are “side by side” on a wavelength chart. Blue light emits wavelengths between 455 to 492nm. Green picks up where blue left off, having a wavelength between 492 and 577. From this perspective, it’s not as bad as blue, but also not ideal.
Plus, if you think about what we said earlier — that we’re most sensitive to green light — it means green light could actually be worse for your sleep patterns than blue light.
Cool night vision gadgets
Now that night vision tech is available to the general consumer, we thought it would be a good idea to look at some common night vision gadgets you can buy right now. As with any online purchase, be sure to read reviews before making a decision.
Night vision glasses
Do you struggle with seeing a star pattern around lights at nighttime? Chances are, you suffer from astigmatism. A great way to combat this is to invest in a quality pair of night vision glasses. They’ll use the same basic light intensification technology (minus the thermal and active illumination components) in conjunction with anti-glare coatings to minimize the distractions from headlights and maximize your sight.
Night vision security cameras
Traditional security cameras work great during the day when there’s lots of light available. When you’re shopping around for your next setup, consider investing in cameras that also include a night vision mode. These should be able to differentiate between daytime and nighttime (based on a built-in timer or light sensors).
These can be especially beneficial if you live in the country and only have one security light. They keep an eye on the darker areas of your property so you can feel safe and secure at all times!
Night vision scopes
Are you a hunter looking to maximize your skills during the early morning hours? Consider investing in a night vision scope. Just like any night vision tech, these will help you see just where that elusive 12-point buck is hiding!
Night vision: the practical solution
Sometimes, it’s helpful to understand the why behind something so we can better understand how it can help us. We hope you now have a much better understanding of why night vision is green. It’s not a directorial decision to set the tone of an action movie. There are practical, real-world reasons why scientists developed green night vision goggles for our military. The human eye is most sensitive to the color green, and the phosphor component of night vision technology works to amplify that!