Clicky

How does Night Vision Work?

Is night vision really as good as they make it in the movies? In today’s post we explain all about the technology and find out just how effective night vision really is.

night-vision-goggles

What is the first thing that comes to mind when you hear the term, night vision? You probably think back to all of those James Bond-type movies you have watched, and the cool gadgets that were used. Well, fact is often stranger than fiction, and there is a lot of cool science behind night vision goggles.

Yes, they do work, and yes, they will help you to see things in the dark, as long as there is at least a minimal source of light. In fact, while wearing night vision goggles, you can see objects as far as 200 yards (83 meters) away. So, how does night vision work? Let’s find out.

Two Types of Technology

There are two types of technology that are used in night vision. The first is image enhancement, which works by collecting small particles of light from the full spectrum, including the infrared (IR) spectrum. These bits of light may not be visible to the naked eye, but when they are enlarged through night vision technology, we are able to see images.

The other technology used in night vision is thermal imaging. This works by taking the upper part of the infrared spectrum, which is emitted as heat instead of just light. The hotter the object, the easier it will be to see it using thermal imaging.

Understanding How Light Works

Before we can really get into learning about night vision, it is important to learn something about light itself. How much energy that is in a light wave is directly proportional to the wavelength. The shorter the wavelength, the higher the amount of energy, and vice versa. When it comes to visible light, the color with the highest amount of energy is violet, and the color with the least amount of energy is red. At the far end of the light spectrum, beside the visible spectrum, is what is known as the infrared spectrum.

light spectrum

What is Infrared Vision?

While most night-vision goggles use thermal imaging, security cameras usually use infrared night vision technology. Take a close look at a security camera, and you will notice a number of tiny LED bulbs. These bulbs are the infrared light. When the sky becomes dark, these lights will come on, and give the camera plenty of infrared light to capture images. This light is invisible to us, so we don’t actually see a bright light, but the camera sees it.

So, if it is infrared, why is the footage from security cameras black and white? The main reason for this is because the human eye is better equipped to see black and white than colors, particularly red and blue. The monochromatic images make it easier for us to see what has been recorded. These days, most security cameras using infrared technology also use what is known as an infrared cut filter. This is going to detect daylight and ensure that infrared light is blocked, so that colors look true. At night, the filter will automatically be removed so the infrared light technology can go to work.

There are actually three different types of infrared light:

  • Near-Infrared (near-IR) – This is the next best thing to visible light, with wavelengths ranging from 0.7 microns to 1.3 microns.
  • Mid-Infrared (Mid-IR) – The wavelengths range from 1.3 microns to 3 microns. Along with near-IR, mid-IR is often used in many types of electronic devices, such as remote controls.
  • Thermal-Infrared (Thermal-IR) – This is the largest part of the IR spectrum, with wavelengths ranging from 3 microns to 30 microns or more.

There is one distinct difference between thermal-IR and the other two types of infrared light, and that is the fact that this type of light is emitted by objects instead of being reflected by them. This is due to things going on at the atomic level.

How does Thermal Imaging Work?

A special lens is used for thermal imaging that focuses the IR light emitted by all objects in its field of view. This light is scanned by IR detector elements which create a temperature pattern. This pattern is what is known as a thermogram. You may be surprised to learn that the detector only needs a thirtieth of a second to create the thermogram, via information from thousands of points. It is created by these elements, which are then translated into electronic impulses.

thermogram image of a person

Thermogram image of a person

A circuit board collects all of the electronic impulses. This circuit board has a dedicated chip that will translate the information collected and turn it into display data. This data can be seen in a variety of colors, depending on how intense the infrared is. All of the electrical impulses when combined will form an image.

Two Types of Thermal Imaging Devices

There are two main types of thermal imaging devices: uncooled, and cryogenically cooled. The most common type is uncooled, where the infrared-detecting elements are housed in a single unit that works at room temperature. Cryogenically cooled imaging devices are much more costly, as they can be damaged more easily. The elements are inside a sealed container, which is cooled to below 32F (zero degrees Celsius).

Why does the cryogenically cooled system work so well? For one thing, you get much better image resolution. These systems are able to detect differences as minute as 0.2F (0.1C), from as far as 1,000 feet or more. These are the systems that are typically used by law enforcement agencies, because they are able to pick up so much detail at a distance.

Types of Night Vision Devices

There are three different types of night vision devices. Scopes are generally hand-held, or they can be mounted onto rifles and other weapons. These have one eye-piece and are often used when someone wants to see an object and then immediately go back to normal vision conditions.

Nightvision through image intensifier

View through an image intensifier from 2003 Iraq War

One of the more popular types of night vision devices is goggles. These are binocular and can have either single or stereo lenses. These are used when you need constant night vision. Finally, cameras also have night-vision technology. They send the images to monitors, where they can be displayed or recorded.

Choosing the Right Night Vision Device

There are a number of things to consider before you go out and buy a night vision device. For instance, what type of environment will it be used in? You need to consider the distance you will be from the objects that you want to see, as different types of goggles work at different distances. If you don’t need to see things in the distance, you can get away with spending a lot less on your night vision goggles. Weather is another consideration, as it can affect levels of light and visibility. Other things to consider when choosing night vision goggles include:

  • Gain – The gain is the level of light you will see when viewing images through the device. The more magnification, the worse the gain is going to be. Look for a set that has high gain.
  • Image Quality – Obviously, the better the image quality, the easier it is going to be to see the images.

Image quality and gain go hand-in-hand, so it is important to choose a device based on the application it will be used for. If you are going to be doing any night-time hiking or other adventures in the dark, it is best to choose a device that has plenty of gain and excellent image quality.

How do Night Vision Goggles Work?

There are different kinds of night vision goggles. There are some that pick up the tiniest amounts of light, including invisible infrared light, and they allow us to see what is around us through image enhancement. More popular are night vision goggles that use thermal imaging technology, which locks onto heat emitted by objects. The heat waves are seen as infrared light, which is picked up by the goggles. Objects that are hotter are going to appear more clearly, while cooler objects will be darker.

Night vision goggles have three main parts:

  • Photocathode in the front of the goggles, located near the lens
  • Photomultiplier near the middle of the lens
  • Phosphor screen at the end near the eyes

In theory, photons (light made from subatomic particles) go through the front lenses, hitting the photocathode. This turns the photons into electrons, or light into electricity. The electrons travel to the photomultiplier, which increases the number of electrons, which move on to the phosphor screen, which converts the electrons back into photons. The light is enhanced, and this is what helps you to see in the dark.

However, there are many different types of night vision goggles available on the market, and some work a little differently. For instance, some may have 1X magnification. This doesn’t mean that objects are enlarged. It means that there are more light particles picked up, so the image is more accurate and you have better depth perception while moving around. Some night vision goggles are made with plastic lenses that are cheap and have one or even no layers of coating. These aren’t going to work nearly as well as goggles that are made with glass lenses, which have multiple coating layers for brighter images.

What if there is No Light Around?

So, what happens if there is no light for night vision goggles to detect? Are they are going to work when you are in complete darkness? The only way that you are going to be able to see anything is if your goggles have thermal imaging. This is what is used by rescue workers who have to be in dark spaces, such as firefighters who are surrounded by dark smoke. Thermal imaging night vision goggles will notice temperature differences and render various colors in accordance with the various temperatures. If something appears red, you know that it is hot, while a blue image is going to be cold. In-between shades will be seen in various shades of cool and warm colors.

thermal imaging in an airport

Thermal Imaging in Airport Security

There is another way that night vision goggles detect images. Warm objects do not emit infrared light, but they do emit infrared radiation, which is lower in frequency. Night vision goggles have CMOS or CCD sensors that will pick up on the radiation, decoding it and turning it into photons.

So, which type of night vision goggles do you need? It all depends on what you are using them for. If you are going on outdoor adventures, you will probably want to choose goggles that have image enhancement technology. If they are to be for professional use, such as being used in search and rescue missions, a better option would be night vision goggles with thermal imaging technology.

Why are Night Vision Goggle Images Green?

You may be wondering why the images seen through night vision goggles are green. There is definitely a method to this madness, just as an IR camera has black and white images. Our eyes are sensitive to green light, so we are able to better see details. Also, green light is easier to look at for longer periods of time without risking eye fatigue. Since night vision goggles were first developed for the military, and to be worn for extended periods of time, they were designed to have light that was the most comfortable to look at for any length of time.

Summary

You can’t amplify light, but you can use night vision goggles that use a clever trick. By converting light to electrical impulses, the signal can be boosted before being converted back to an image that we can see much more clearly. 

An intensifier tube takes photons (light) and turn them into electrons, before a photomultiplier boosts those signals. Finally, these electrical signals are sent to a phosphorous screen, which converts these signals back into light.

With security cameras, the ideal images are going to be produced in black and white. But, when it comes to night vision goggles, you want something that is going to have thermal imaging.


Take a look at our guide to the best monoculars. We’ve got a special section on the top night vision models too.

If that’s not enough information for one day, we’re sure you’ll love our guide to stealth technology too.

Don’t forget to bookmark us as we’ve got lots more coming at stealthyninjas.com over the next few weeks and months!

Image Sources

By Inductiveload, NASA [GFDL or CC-BY-SA-3.0], via Wikimedia Commons

By Etan Tal [CC BY 3.0], from Wikimedia Commons

By AlexPlank at English Wikipedia (transferred from en.wikipedia) [Public domain], via Wikimedia Commons

Let us know what you think down in the comments!

      Leave a reply