How Do Night Vision Goggles Work? (There's 3 types)

- What happens when you take the world's best

night

vision

goggles

into the darkest room in the world? - You're starting to feel a little weird. And sometimes you start to feel a little dizzy. - Can you tell the difference between having your eyes closed and open? - I shouldn't be able to do it. It will be this dark. - Three. There is basically no light here. - Two. - There are almost no photons. Invisible. That's how it is. - One. - Oh, I'm ready. - Total darkness. (laughs) No way. This is crazy. These are the PVS-31A.

That is incredible. One of the best

night

vision

glasses in the world. It's literally like day and night. We visited a naval base in Crane, Indiana, to put them to the test in all

types

of darkness. Now things will become real. It's the first time I look through night vision

goggles

. - I'm going to analyze them. - Oh, wow. (laughs) Oh my God. To make a video about night vision goggles, we had to film in complete darkness, which is really difficult, because cameras

work

by focusing photons of light onto a sensor. And there, the photons give off electrons, generating a charge, which is converted into voltage and digitized into ones and zeros for each pixel.

Now, there's a setting that we use, called ISO, that essentially increases that voltage to make the entire image brighter. For reference, this is what a scene lit only by a candle looks like at a high ISO of 6,400. Now, on a split screen, let me show you what this looks like at an ISO of 64,000. Now you can see much more detail in the shadows. This is quite similar to the level of detail the human eye can see in low light situations. And now this is what it looks like with our camera's maximum ISO of 409,600. All dark scenes in this video were recorded at this maximum ISO.

But look how dark it is compared to a single candle. This is because the Navy base was located in the middle of nowhere and we turned off all the street lights. Alright. Additionally, we planned the shoot specifically for a moonless night. Under these conditions, I will try to drive a military tactical vehicle with nothing but night vision goggles to see. I hope it's up and running. But the type of night vision goggles you use is essential. All affordable night vision goggles

work

the same way and are basically the same as putting a flashlight on your head.

Except the light they emit is not visible, but near infrared, wavelengths that are a little longer than our eyes can see. They then have a camera that can capture that near-infrared light and display what the camera sees on a screen on the back. This is the simplest and cheapest version of night vision. It's called active lighting. There are actually three different

types

of night vision. - Night vision includes different categories of technologies: those that create their own light, those that amplify existing light and those that generate images in the emitting infrared bands. - And while other types of night vision can cost thousands of dollars, our active illuminators cost less than $200.

It's very expanded, I think. (laughs) - Isn't it one on one? - It's not a one-on-one. Because they are much cheaper and easier to manufacture than any other type of night vision, active illumination is what is used in almost all commercial night vision goggles or night security cameras. These were the first night vision goggles I used to try driving in pure darkness. I have no idea where the focus is. If you could see this, you would be terrified. I'm looking at the road and my focus is on the first cone. My God, this is not advisable.

I have no idea how fast we are going. The problem with these glasses is that they feel too close up. They're bouncing and they're not really bouncing in time with anything. It's like bouncing. If we hit a parked car right now, I wouldn't be surprised. - Oh God. - Okay, sure. Straighten it. - Direct, straight. - Right? - Fix it up. -Ben has military night vision goggles on, so he can see where we're going. - Further to the left, further to the left. Yes. And we're probably fine. - Oh! If they hadn't directed me from behind, we would have crashed many times.

I also feel a little sick. So there's that. This is one of the big drawbacks of active lighting. There is a significant delay between what the camera sees and what is displayed on the screen. - For most digital systems, the fastest you can get is the frame rate. So if it's 24 frames per second, the fastest you could be on lag is about 1/24th of a second. Tens of milliseconds, maybe. - That's enough to make people dizzy and lose coordination. Oh boy. Do you want to throw me a Frisbee? (naughty music) (Frisbee scraping) - (laughs) You're not even moving. - I can not see anything. (naughty music) (Frisbee scraping) (Emily laughs) I think I'll have to take these off soon.

There's this crazy roller blind and everything moves in front of me. Another drawback of active lighting is that its range is limited, since you can only see as far as the light reaches. But the main reason you can't use them in the military is simple. They are not passive. There is a bright infrared light beacon nearby, so enemies can easily spot you. In fact, military night vision goggles are a totally different technology. But they can still see in the near infrared. And that's why we've been shooting through them to capture the light from the active illuminators.

Have you ever gone out at night with night vision goggles on and seen someone who has an active lighting device? - Yes, there are no comments on that. - (laughs) Fair enough. Military night vision goggles need to be much more concealed, which is why they do not use active illuminators. Instead, they rely exclusively on the second type of night vision: image intensification. So should we try some good glasses now? Oh my God. It's literally like day and night. Alright, let's do this. (uplifting music) - Oh, he left with a lot of confidence. - Because I can see. - Oh Lord. - I'm going straight to the cone.

I'll go to the left of this cone and then pass between them. Oh yeah. - Oh. - It's like driving during the day. This technology uses only the existing light in a scene. When photons enter glasses, like these PVS-31A, they are physically amplified, so more photons come out the other end to reach your eyes. And in terms of how much brighter it makes the light, can you comment on that? - Yes, they are definitely at least on the order of thousands. - Thousands of times brighter. - Yes. - And they are very light, so people can wear them for more than 10 hours straight.

All powered by a single AA battery. Driving the vehicle was now super easy. So easy that I trusted it a little. - Maybe a little slower in the corner. - Well. And since the glasses don't use a camera or screen, there's almost no delay in what you see. So you can shake the glasses and the world moves with you. - The time between the light entering and the light leaving is very short. You can go down to microsecond levels, maybe even faster. Nanosecond levels. - It's as if there were no protective glasses there. No, I can see incredibly well.

Let me compare it to something like, without night vision. Oh my God. Man, the world looks so much better through these glasses. That's when we discovered an unexpected benefit of night vision. (ethereal and delicate music) The stars are phenomenal. Through the glasses, the starlight is amplified enough to illuminate the entire environment. This also means that the entire night sky is revealed in all its glory. Emily, you'll be surprised when you see this. - Oh Lord. You can see so many satellites. Oh, and you can see the Milky Way very clearly. Well. Yes, I can drive with this.

My God, this stretch is beautiful. And it all feels like you're driving on snow. Everything is bright and white. It's so fun. Honestly, I find it really relaxing. - The only problem I noticed is that these night vision goggles have a limited field of view. In reality, you don't have any peripherals. - None None. I think I can, right now, with my hands, I can get here. - But the Navy has an even better pair of glasses than the ones we've been wearing. (mysterious music) These are the GPNVG-18. They also use image intensification, but now it is applied to four tubes to fill the field of view. - The way this optic combines the four tubes, it combines them into a kind of ellipse in the eye so that you can look with your eye from side to side, without having to move your head. - They are the most expensive NVGs in the world.

They sell for over $40,000 online. They are also the same glasses that were used in SEAL Team Six's attack on Osama bin Laden in 2011. (engine roaring) That's incredible. Yes, I would be happy to do anything with these glasses. Yeah! It just gives you a lot more confidence to be able to see. The last thing that makes these military glasses look so natural is their incredible resolution. - When we characterize a night vision tube, we don't think in terms of pixels or resolution in that sense. We think of it in terms of pairs of lines per millimeter. So how many pairs of lines can you resolve in a millimeter of physical space? - For a pair of night vision goggles to be military grade, they must be able to resolve at least 64 pairs of lines per millimeter. - So, there is an almost qualitative, but very skillful and historical process on how your performance is quantified. - It's like years of training, or is it... - I would say that within six months we could have someone up to speed. - Wow. - For this I'm going to go completely dark. - Okay, there's a shiny graph in there.

It says plus two on one side. Does it say that? - Maybe you can't say what you really say. - Well. I won't say what it really says. - We run into this problem a lot. - Oh, I can't really answer that. Yes, no comments on that. (Derek laughs) I can't comment on that. So the process to make the microchannel plate and the photocathode, yeah, we can't talk about that either. - (laughs) Much of the night vision goggles are a secret, as they are still state-of-the-art. This video is the absolute limit of what the Navy is willing to publicly reveal about its night vision.

Although we cannot show the exact bar test, we can show it. - You see bars similar to what we had in night vision here, through the trees. And then we have, if maybe we go to this other corner, we could see at different distances. And the bigger the optic gets, the farther you'll be able to see. Therefore, you need increasingly distant calibration targets to understand the resolution and quality of those images. We do a lot of characterization and lab modeling to predict how far you'll be able to see, but the ultimate test is getting out into the real world. - We use pairs of lines per millimeter to describe the resolution of the glasses because image intensification is analog, not digital.

This is the secret of how they emulate our normal vision so well. Digital cameras have refresh rates and resolution limits to worry about because they convert photons into discrete values ​​in pixels. But image intensifiers are a continuous, real-time, one-to-one way to amplify light. Is that how it works. In a dark scene, limited light from things like stars reflects off the scene and sends some photons toward the image intensification tube. The lens focuses these photons into the tube as an inverted image, where they pass through three steps. First, the photon hits a thin plate called a photocathode, made of semiconductors or alkali metals.

When a photon hits the plate, an electron in that part of the plate is excited and ejected into the vacuum. The electrons are then accelerated through the vacuum tube using a voltage. They head directly into another thin plate, called a microchannel plate, and it is made of insulating material, often glass, with around 6 million small channels. They all have an angle of about five degrees so that the incoming electrons collide with the walls of the channel. When they do so, they release more electrons from the wall material, which further collide with the walls, releasing more electrons and creating an electron avalanche.

Then a few electrons enter and an avalanche of thousands leave. This avalanche of electrons then leaves each channel and is accelerated in a straight line by another high voltage to hit a phosphor screen. This is just a screen made of a material that glows when exposed to radiation. It then converts the kinetic energy of the electron back into visible photons for you to see. So each photon entering the tube is multiplied thousands of times while maintaining its position, resulting in a brighter but otherwise identical image. As a final step, there are 20 million optical fibers attached to the phosphor screen that twist the image upwards. (soft music) - The photocathode, the microchannel plate, that vacuum space, the phosphor screen, it's all in this first section.

About the width of my fingernail. The rest of this space is the fiber optic turn. - Oh, wow. For decades, the phosphor screen was always green. It is this historic choice of phosphor that is responsible for all the classic green night vision we know frommovies or video games. But in dark conditions the human eye does not see better in the green part of the spectrum. There are two types of photoreceptors in the retina: rods and cones. Cones are best for well-lit vision and are good at distinguishing colors. They are located in the center of the retina.

Rods are best for low-light vision and are located at the edges of the retina. This is why you can sometimes see faint stars out of the corner of your eye, but they disappear if you look directly at them. The light sensitivity of rods peaks in the blue part of the visible spectrum. That's why our PVS-31As look like this. They have been upgraded to white phosphorus, which generally looks slightly blue, making it easier for people to distinguish. To see how well these night vision goggles amplify light, we placed them in a well-lit room and covered them completely, except for a small hole for a thumbtack.

This lets in just a little bit of light. But the view through the glasses is even brighter than the room itself. We couldn't expose the night vision goggles to more light than this, but not for anything like movies, where bright light is enough to incapacitate people wearing night vision goggles. - So what would happen if we turned on the lights without the cap? Would this just turn white? - It would still work, but you wouldn't want to do it for a very long period of time. It has a current limiter on the amount of charge that the screen can absorb, and increasing the intensity of the light saturates that component of the circuit. - But what happens if we take image intensification to the opposite limit, using the glasses in a room without light?

If you want to try night vision goggles, you need to go somewhere where it's completely dark, underground, all sealed, basically no photons. It's going to be completely disorienting. - So we're at an underground firing range here at the naval base, Crane. And this place is usually used for testing small weapons, but we can also seal it and make it very dark, to where there is almost no visible light. - So basically there is no light here, almost no photons. - In the visible. That's how it is. - Now we're going to turn off all the lights, make it completely dark here, but on top of that, the kitchen is full of smoke.

So even with night vision goggles, we might be out of luck. If you are in pure darkness for a long period of time, what happens? - You're starting to feel a little weird. It's like being in an anechoic chamber, where you can't hear anything. The lack of sensory perception can sometimes start to cause a bit of vertigo or a feeling of restlessness in some people. - Well. - Three, two, one. - Total darkness. Okay, my night vision is on. - Wow, I can't actually see anything through these. - With the PBS-31As in pure darkness, you mainly only see their analog processing in effect. - My God, it looks like a blizzard. -When I look in that direction, I see almost nothing.

Only snow falls on me. All this noise comes from electrons passing through the glasses in two ways. One is thermionic emission. Just because of the thermal energy, some electrons will have enough energy to escape from the metal. And the other is due to the electric field. There is such a strong electric field in that tube that it will knock some electrons off the photocathode. Can you make out the face? Because I mean, there's a little bit of light coming out of the glasses, which could hit me in the face. Since image intensification can only amplify existing light, its only limitation is that it requires a light source.

It may be tiny, but there has to be something. If you are in complete darkness, even active lighting is a better option. Now this is a plus because if you are in a very black room then you need to brighten it up a bit. Unless you use the latest type of night vision: thermal imaging. I can't make out the exit sign with the naked eye, but with my glasses I know it's up there. While image intensification attempts to match your normal vision, thermography goes further. In the electromagnetic spectrum, the infrared range has longer wavelengths than the visible range.

All shorter wavelengths up to mid-wave infrared light are reflective, meaning that everyday objects do not emit these wavelengths on their own. You need a light source. To see my shirt, we can't be in the dark. You need visible light to reflect blue into your eyes. And that's why we needed near-infrared lights in active lighting fixtures. But long-range infrared is actually emissive, meaning it doesn't need any light source. This is because all objects emit electromagnetic radiation and the shape of their spectra follows Planck's law. It can be seen that only extremely hot objects, such as stars, have significant emissions at shorter wavelengths, such as visible light, but virtually everything emits in the infrared.

Because thermal imaging does not require any external light, as image intensifiers do, and does not need to create its own light, as active illuminators do, it is invincible in completely dark situations such as the underground field. It is also the best option when there is fog or smoke obstructing the view. I'm about to walk into the fog at this range, and we'll see if I disappear into the visible, and then you guys can look and see if we can catch me on the infrared cameras. - Yes, I can't see you now. (naughty music) Derek is doing the full workout on him. - Oh!

I had no idea we would be so emitting down there. Thermal imaging also sees things your eyes could never see, such as objects buried underground or recently touched by someone's hand. The last advantage of thermography is its unbeatable range, even better than that of military night vision goggles. We organized a distance test hundreds of meters from the tower to compare the infrared cameras with the PVS-31A. To the naked eye, on a moonless night, this is what someone holding a lighter looks like at that distance. This is what it looks like through night vision goggles. And this is what it looks like through infrared cameras.

To be even more subtle and eliminate all direct light, this is what a person checking their phone looks like in those conditions. Completely invisible to the naked eye, perceptible through night vision goggles and perfectly clear through infrared cameras. But thermography also has its weaknesses. It is a digital system with motion delays just like active lighting. Thermal glasses are not popular because high-quality infrared cameras are too large and consume too much power to be portable. And since they only detect thermal radiation, they can't even see, for example, the letters on signs. This is looking at it in infrared.

E, F, P, T, O, Z, L, P, E, D. Anything that is visible only by the way light is reflected is invisible to thermal cameras. E, D, F, C. I don't know what that is. Z, F or Z, P. (bells ringing) There is currently no best type of night vision. They all have trade-offs between things like resolution, lag, lighting situation, concealment, and portability. The entire history of night vision has been driven by the attempt to minimize these trade-offs. The first night vision technology, known as Gen 0, was developed for sniper scopes during World War II and the Korean War.

They used active infrared lighting, much like today's commercial night vision goggles. Gen 1 night vision was then developed for the Vietnam War. These used basic image intensifier tubes with only a photocathode and a screen. Without microchannel plate. They stacked three of them in a row, making them extremely bulky and distorted when looking through them. But the resulting scopes were sensitive enough to operate just outside the light of the Moon and stars, giving them the nickname Starlight. Gen 2 night vision was developed in the 1960s and 1970s and added the microchannel plate to the image intensifier tube, increasing sensitivity so they could be used in dark conditions, such as cloudy or moonless nights.

This addition also made the tubes much more compact, allowing the first sets of portable night vision goggles to be created. The last generation, Gen 3, was available in the late 1980s. These changed the photocathode material to semiconductor gallium arsenide to better convert photons into electrons. They also coated the microchannel plate with an ion barrier film to increase the tube's lifespan from 3,000 to 10,000 hours. Although there hasn't been an official new generation of night vision goggles in over 30 years, researchers are constantly working on new improvements. - Some of the research basics I can talk about are how to extend the infrared regime of detectors in general.

We are looking for areas to have devices that can see further into the infrared with less noise than we can see today. - How did you get into night vision goggles? - I was in the Marine Corps in the early 2000s, and we were still using a model similar to this here in Operation Iraqi Freedom. That was one of the factors that really drove why I got into this field. I was using things like this that were good, but not great. You know, they could have been better. We also used infrared systems which were not good at all.

And then, using them in the field and feeling, you know, asking yourself that question, why isn't it better? - And the value of night vision extends far beyond the military realm. What types of applications would people use these glasses for? - Search and rescue or places where there may be no power. It's too dark to see and you want to be able to get things done quickly. - Thermal imaging has grown into an entire industry, with infrared cameras used in everything from firefighting to building inspections and medical imaging. And the microchannel plate initially developed for night vision is now found aboard space telescopes, such as the Chandra X-ray Observatory, helping us discover the hidden world beyond what is simply visible to the naked eye. - Wow, that's beautiful.

I have tears in my eyes. It's okay, I'm fine. (laughs) I feel like no one can see me because I'm in the dark, but you probably can if you have night vision on. (soft piano music) (machine hum and trill) - Trying this night vision technology perfectly illustrates how there is no substitute for hands-on exploration to truly appreciate new innovations. But you don't have to go to a military base to get to work with cutting-edge technology. - In fact, you can do it from anywhere with this video sponsor, Brilliant. And you can start for free today. Just go to shiny.org/veritasium.

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