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

• What happens when you take the world's best night vision goggles into the world's darkest room?
• You start to feel a little strange. And sometimes start to get a little bit of vertigo.
• Can you tell the difference between your eyes being closed and open?
• Should not be able to. It'll be that dark.
• Three - Basically zero light in here.
• Two.
• Almost no photons. Invisible. That's right.
• One.
• Oh, I'm ready.
• Pitch darkness. (laughs) No way. This is insane.

These are the PVS-31As. That is incredible. One of the best night vision goggles in the world. It is literally like night and day. We visited a Navy base in Crane, Indiana, to put them to the test in all kinds of darkness.

Now things are gonna get real. It's my first time looking through night vision goggles.

• I'm going to pan these down.
• Oh wow. (laughs) Oh my God.

To make a video about night vision goggles, we had to film in the pitch dark, which is really hard because cameras work by focusing photons of light down onto a sensor. And there, the photons knock off electrons, generating a charge, which is converted into a voltage and digitized into ones and zeros for each pixel.

Now, there's a setting we made use of, which is called ISO, which essentially boosts that voltage to make the whole image brighter. For reference, this is what a scene lit only by a single candle looks like at an elevated ISO of 6,400. Now, in a split screen, let me show you what this looks like at an ISO of 64,000.

Now you can see a lot more detail in the shadows. This is pretty similar to the level of detail that the human eye can see in low-light situations. And now this is what it looks like on our camera's maximum ISO of 409,600. All the dark scenes in this video were shot at this maximum ISO. But look how dark it is compared to just a single candle.

This is because the Navy base was located in the middle of nowhere, and we turned off all the streetlights. All right. Plus, we planned the shoot specifically for a moonless night. In these conditions, I'm gonna try to drive a military tactical vehicle with nothing but night vision goggles on for sight.

I hope that's in drive. But the type of night vision goggles you use is essential. All affordable night vision goggles work the same way, and they're basically the same as strapping a flashlight onto your head. Except the light they give off is not visible, but near infrared, wavelengths that are just longer than our eyes can see.

Then they 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 illumination. There are actually three different types of night vision.

• Night vision is different categories of technologies: ones that create their own light, ones that amplify existing light, and ones that image in the emissive infrared bands.

And while the other types of night vision can cost thousands, our active illuminators cost less than $200. It's very zoomed in, I feel like. (laughter)

• It's not a one-to-one?
• It's not a one-to-one.

Because they're far cheaper and easier to make than any other kind of night vision, active illumination is what's used in almost all commercial night vision goggles or nighttime security cameras. These were the first night vision goggles I wore to attempt to drive in pure darkness.

I have no idea where the focus is. If you could see this, you would be terrified. I'm looking out at the road, and I have the focus set to the first cone. Oh my goodness, this is not advisable. I have no idea how fast we're going.

The problem with these goggles is it feels very zoomed in. It is bouncing, and it's not really bouncing in time with anything. It is just like, bouncing. If we hit a parked car right now, I would not be surprised.

• Oh God.
• Okay, straight. Straighten it out.
• Straight, straight.
• Straight?
• Straighten it out.

Ben has military night vision goggles on, so he can actually see where we're going.

• More to the left, more to the left. Yep. And we're probably good.

• Oh! If I hadn't been directed from behind, we would've crashed so many times. I also feel a little bit sick. So there's that.

This is one of the big drawbacks of active illumination. There's a significant delay between what the camera sees and what's displayed on screen.

• For most digital systems, the fastest you could ever get is the frame rate. So if it's 24 frames per second, the fastest you could be in the delay is about 1/24 of a second. Tens of milliseconds, maybe.

That's enough to make people get motion sickness and lose their coordination.

Oh boy. Do you wanna throw me a Frisbee? (mischievous music) (Frisbee scraping)

• (laughs) You don't even move.
• I can't see anything.

(mischievous music) (Frisbee scraping)

(Emily laughs) I think I'm gonna have to take these off shortly. There is crazy rolling shutter, and just everything's jiggling around in front of me. Another drawback of active illumination is that your range limited since you can only see as far as the light shines.

But the main reason you can't use these in the military is simple. They aren't passive. There's a bright beacon of near-infrared light, 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 this is why we've been filming through them to capture the light from the active illuminators.

Have you ever been out at night with night vision goggles and sort of spotted someone who's got like, an active illumination device?

• Yeah, no comment on that one.

• (laughs) Fair enough. Military night vision goggles need to be far more concealed, so they don't use active illuminators. Instead, they rely exclusively on the second type of night vision: image intensification.

So should we try good goggles now? Oh my goodness. It is literally like night and day. All right, let's do this.

(exhilarating music)

• Oh, he's off with so much confidence.
• Because I can see.
• Oh my god.
• I'm going straight for the cone. I'm gonna go to the left of this cone, then I'm gonna go in between them. Oh, yes.
• Whoa.

It's just like driving in the day. This technology uses only the existing light from a scene. When photons enter goggles, like these PVS-31As, they get physically amplified so that way more photons come out the other end to reach your eyes.

And in terms of like, how much brighter it makes the light, can you comment on that?

• Yeah, it's definitely at least on the order of thousands.

• Thousands of times brighter.

• Yeah.

And they're very light, so people can wear them for more than 10 hours straight. All powered by a single AA battery. Driving the vehicle now was super easy. So easy that I got a little bit overconfident.

• Maybe a little slower on the corner.
• Okay.

And since the goggles don't use a camera or display, there's almost no delay in what you see. So you can shake the goggles, and the world just moves with you.

• The time from light in to light back out is very short. You can get down to microsecond levels, maybe even quicker. Nanosecond levels.

It's as if there are no goggles there at all. No, I can see so incredibly well. Let me compare to like, no night vision. Oh my goodness. Man, the world looks so much better through these goggles.

This is when we found an unexpected benefit of night vision. (delicate ethereal music) The stars are phenomenal. Through the goggles, starlight gets amplified enough to light your entire environment. This also means that the entire night sky gets revealed in its full glory.

Emily, you are gonna have your mind blown when you see through these.

• Oh my god. You can see like, so many satellites. Oh, and you can see the Milky Way so clearly. Okay. Yeah, I can drive with this. Oh my god, this stretch is gorgeous.

And it all looks like you're driving in snow. Like, everything is sparkly and white. It's so fun. Honestly, I find it really relaxing.

• The one problem I noticed is that these night vision goggles have a limited field of view. You got no peripheral, really.
• None, none. I think I can, like, right now with my hands, I can get up to like, this far.

But the Navy have one set of goggles even better than the ones we've been using. (mysterious music) These are the GPNVG-18s. They also use image intensification, but now it's applied to four tubes to fill your field of view.

• The way this optic is combining the four tubes, it's combining it into one sort of ellipse into your eye so that you can look with your eye side to side, without having to move your head.

They're the most expensive NVGs in the world. They retail for over $40,000 online. They're also the same goggles that were used in the SEAL Team Six raid on Osama bin Laden in 2011.

(engine roaring) That's amazing. Yeah, I'd be happy to do anything in these goggles. Yes! It just makes you so much more confident to be able to see.

The last thing that makes these military goggles feel so natural is their incredible resolution.

• When we characterize a night vision tube, we don't think about it in terms of pixels or resolution in that sense. We think about it in terms of line pairs per millimeter. So how many line pairs can you resolve within one millimeter of physical space?

For a pair of night vision goggles to be military grade, they need to be able to resolve at least 64 line pairs per millimeter.

• So there's a almost qualitative-like, but very skilled and historic process for how these are quantified for their performance.

• Is it like years of training, or is it...

• I'd say within six months we could have somebody up to speed.

• Wow.

• For this I'm gonna go completely dark.

• Okay, there's a bright chart right in there. It says plus two on one side. Does it say that?

• Maybe can't say what it really says.

• Okay. I won't say what it really says.

We ran into this issue a lot.

• Oh, I can't really answer that. Yeah, no comment on that one.

(Derek laughs) I cannot comment on that. So the process to make the microchannel plate and the photocathode, yeah, we can't talk about that, either.

• (laughs) So much about the night vision goggles is a secret, since they're still cutting edge. This video is the absolute limit of what the Navy is willing to reveal publicly about their night vision.

Though we're not allowed to show the exact bar test, we can show these.

• You see similar bars that we had in the night vision are out here, through the trees. And then we've got, if we maybe go towards this other corner, you could see at different distances. And the bigger the optic gets, the farther away you can see.

And so you need farther and farther away calibration targets to understand the resolution and the quality of those images. We do a lot of lab characterization and modeling to predict how far it'll be able to see, but the ultimate test is to come out into the real world.

• We use line pairs per millimeter to describe the goggles' resolution because image intensification is analog, not digital. This is the secret to how they emulate our normal vision so well. Digital cameras have refresh rates and resolution limits to worry about because they're converting photons into discrete values on pixels.

But image intensifiers are a continuous, real-time, one-to-one way to amplify light. This is 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 onto the tube as an upside-down image, where they go through three steps. First, the photon hits a thin plate called a photocathode, made from semiconductors or alkaline metals.

When a photon hits the plate, an electron in that part of the plate gets excited and is ejected into the vacuum. Next, the electrons are accelerated through the vacuum tube by a voltage. They head straight into another thin plate called the microchannel plate, and this is made from insulating material, often glass, with about 6 million tiny channels in it.

These are all angled at about five degrees to get incoming electrons to collide with the channel walls. When they do, they release more electrons from the wall material, which collide even more with the walls, releasing more electrons, creating an electron avalanche.

So a few electrons go in, and a flood of thousands come out. Then this flood of electrons leaves each channel and gets accelerated in a straight line by another high voltage to hit a phosphorous screen. This is just a screen made of material that glows when exposed to radiation.

So it converts the electron kinetic energy back into visible photons for you to see. So every photon that enters the tube gets multiplied thousands of times over while maintaining its position, which makes for a brighter but otherwise identical image.

As a last step, there are 20 million optical fibers attached to the phosphorus screen that twist the image right side up.

(soft music)

• The photocathode, the microchannel plate, that vacuum gap, the phosphorus screen, is all in this first section. About the width of my fingernail.

The rest of this space is the fiber optic twist.

• Oh wow. For decades, the phosphorus screen was always green. It's this historic phosphor choice that's responsible for all the classic green night vision we know from movies or video games.

But in dark conditions, the human eye doesn't see best in the green part of the spectrum. There are two types of photoreceptors on your retina: rods and cones. Cones are better for well-lit vision, and they're good at distinguishing color. They're located in the center of your retina. Rods are better for low-light vision, and they're located at the edges of your retina.

This is why you can sometimes see dim stars out of the corner of your eye, but they disappear if you look straight at them. The light sensitivity of rods peaks in the blue part of the visible spectrum. So that's why our PVS-31As look like this.

They've been upgraded to white phosphor, which looks slightly blue overall, making it easier for people to make out. To see how well these night vision goggles amplify light, we put them in a well-lit room and covered them up entirely, except for a little thumbtack hole. This lets in only a tiny bit of light.

But the view through the goggles is still brighter than the room itself. We couldn't expose the night vision goggles to any more light than this, but not because of anything like the movies, where bright light is enough to incapacitate people in night vision goggles.

• So what would happen if we just turned on the lights without the cap? Would this just turn white?
• It would still function, but you wouldn't want to do that for a very long period of time. It's got a current limiter in how much charge can be absorbed by the screen, and increasing the light intensity saturates that component of the circuit.

But what happens if we push image intensification to its opposite limit by using the goggles in a room with no light at all? If you want to test night vision goggles, you gotta go to the place where it is absolutely pitch dark, underground, all sealed off, basically no photons.

It's gonna be completely disorienting.

• So we're in an underground range here at the Navy base, Crane. And this place is usually used to test small arms weapons, but we can also seal it up and make it very dark, all the way down to where there's almost no visible light whatsoever.
• So there's basically zero light in here, almost no photons.
• In the visible. That's right.

We are now going to turn off all the lights, make it completely pitch black in here, but on top of that, the range is full of smoke. So even with night vision goggles, we might have no luck at all.

If you are in pure darkness for a long period of time, what happens?

• You start to feel a little strange. Kind of like being in an anechoic chamber, where you can't hear things. The lack of sensory perception can sometimes start to give a little bit of vertigo or uneasy feeling to some.

• Okay.

• Three, two, one.

• Pitch darkness. Okay, my night vision's on.

• Wow, I actually can't see anything through these.

With PBS-31As in pure darkness, you mainly just see their analog processing in effect.

• Oh my god, it just looks like a blizzard.

When I look that way, I see almost nothing. I just get snow.

All this noise comes from electrons getting pulled through the goggles in two ways. One is thermionic emission. Just due to thermal energy, some electrons will have enough energy to escape the metal. And the other is due to the electric field.

There's such a strong electric field in that tube that it'll pull some electrons off the photocathode. Can you make out the face? 'Cause I mean, there's a little bit of light coming out of the goggles, which might hit my face.

Because image intensification can only amplify existing light, its one limitation is that it requires a light source. It can be tiny, but there has to be something. If you're in absolute darkness, even active illumination is a better bet.

Now, this is advantageous because if you're in a really black room, then you do kind of need to light it a little bit. Unless you use the final type of night vision: thermal imaging.

With my naked eye, I can't make out the exit sign, but with the goggles I know it's up there. While image intensification attempts to match your normal vision, thermal imaging goes beyond it.

In the electromagnetic spectrum, the infrared range has longer wavelengths than the visible range. All the shorter wavelengths up to mid-wave infrared light are reflective, meaning that everyday objects don't 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 the blue to your eyes. And that's why we needed the near-infrared lights on the active illumination devices. But the long infrared range is actually emissive, meaning that it doesn't need a light source at all.

That's because all objects emit electromagnetic radiation, and the shape of their spectra follows Planck's law. You can see that only extremely hot objects like stars have significant emission in the shorter wavelengths like visible light, but virtually everything emits in the infrared.

Because thermal imaging doesn't require any external light, like image intensifiers do, and it doesn't need to create its own light, like active illuminators do, it's undefeated in completely black situations like the underground range.

It's also the best choice when there's fog or smoke obstructing your view. I am about to walk into the fog in this range, and we'll see if I disappear in the visible, and then you guys can look and see if we can pick me up on the infrared cameras.

• Yeah, I can't see you at all now. (mischievous music) Derek's getting his full workout.
• Whew. I had no idea we'd be so emissive down there.

Thermal imaging also sees things your eyes never could, like objects that have been buried underground or recently touched by someone's hand.

The last advantage of thermal imaging is its unbeatable range, even better than the military night vision goggles. We set up a distance test hundreds of meters away from the tower to compare the infrared cameras against the PVS-31As.

To the naked eye on a moonless night, this is what someone holding a cigarette lighter looks like at that distance. This is how it looks through the night vision goggles. And this is how it looks through the infrared cameras.

To get even more subtle and remove all direct light, this is what a person checking their phone looks like in those conditions. Totally invisible to the naked eye, discernible through the night vision goggles, and perfectly clear through the infrared cameras.

But thermal imaging has its weaknesses as well. It's a digital system with motion delays just like active illumination. Thermal imaging goggles aren't popular because high-quality infrared cameras are too big and too power hungry to be portable.

And since they only detect thermal radiation, they can't even see lettering on signs, for example.

This is looking at it in the infrared. E, F, P, T, O, Z, L, P, E, D. Anything that is visible solely due to the way light reflects off it is invisible to thermal cameras.

E, D, F, C. I don't know what that is. Z, F, or Z, P.

(bell dinging) Currently, there is no one best type of night vision. They all have trade-offs between things like resolution, delay, light situation, concealment, and portability.

The entire history of night vision has been driven by trying 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 illumination, much like the commercial night vision goggles of today.

Then Gen 1 night vision was developed for the Vietnam War. These used basic image intensifier tubes with just a photocathode and screen. No microchannel plate. They stacked three of them together in a row, making them extremely bulky and distorted to look through.

But the resulting scopes were sensitive enough to operate just off light from the Moon and stars, giving them the nickname Starlight. Gen 2 night vision was developed in the '60s and '70s and added the microchannel plate to the image intensifier tube, increasing sensitivity so that they could be used in dark conditions, like on cloudy or moonless nights.

This addition also made the tubes much more compact, allowing the first sets of handheld night vision goggles to be created. The last generation, Gen 3, became available in the late '80s. These changed the photocathode material into the semiconductor gallium arsenide in order to better convert photons to electrons.

They also coated the microchannel plate with an ion barrier film to increase the life of the tube from 3,000 to 10,000 hours. Though 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 basic research aspects that I can talk about are looking at how to extend the infrared regime of the detectors overall. Looking at areas to have devices that can see farther into the infrared with less noise than what we can today.

• How did you get into night vision goggles?

• I was in the Marine Corps in infantry in early 2000s, and we still used a similar model as this one right here in Operation Iraqi Freedom.

That was one of the actually driving factors of 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 were also using infrared systems that were not good at all.

And so kind of using those in the field and feeling like, you know, asking that question to yourself, why is it not better?

• And the value of night vision extends far beyond the military. What sort of applications would people use these goggles for?
• Search and rescue or places where maybe there's not power. It's too dark to see, and you wanna be able to do things quickly.

Thermal imaging has grown to become an entire industry, with infrared cameras used in everything from firefighting to building inspections, to medical imaging.

And the microchannel plate first developed for night vision now sits aboard space telescopes, like the Chandra X-ray Observatory, helping us discover the hidden world beyond what is simply visible by eye.

• Wow, that's beautiful. I'm like, there are like, tears in my eyes. Okay, I'm good. (laughs) I feel like no one can see me 'cause it's in the dark, but you probably can if you have night vision on.

(gentle piano music) (machine whirring and trilling)

• Testing 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 all the way to a military base to get hands-on with cutting edge tech.

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