How Does Night Vision Work

A night vision device is used when the human eye reaches its limits because the brightness is simply no longer sufficient. Traditionally, night vision devices have only been used by the military or by hunters. But with the rapid technical developments over the last decades, night vision devices have become an affordable tool for various leisure purposes like wildlife observation, nighttime paintball, etc. But how does such a night vision device work, what is the science behind it and how long has this technology been around? In this post, you will learn everything you need to know about the night vision technology.

How does a night vision device work?

If you deal with the topic of night vision equipment, then it quickly becomes clear that there is not only one technique that is used, but different methods. Basically there are three different methods that are used:

  1. The amplification of the remaning weak light
  2. Making the invisible infrared light (near infrared) of the environment visible
  3. Making the heat radiation of the object itself visible

Most night vision devices work according to the second method and make the invisible infrared light of the environment visible and use it to display an image. Therefore these devices are often called residual light amplifiers. This is also the method everyone knows from these greenish images in movies.

How does night vision work
A typical image obtained through a night vision device. Photo: Flickr

But how does this method work?

The infrared radiation hits a photocathode on one side (facing the object). Electrons are released from it and accelerated by high voltage in a vacuum tube. On the other side of this tube they hit a fluorescent screen and produce the familiar greenish image by fluorescence. This is a very simple explanation of how a night vision device that makes use of the invisible infrared light works.

If the existing invisible infrared light is not sufficient to obtain a “clear” image, the surroundings and the object can be additionally illuminated with infrared lamps. These infrared lamps also use light that is invisible to the human eye.

Since infrared lights are quite cheap to produce, most night vision devices contain an active infrared-light source to enhance the device.

Historical development of night vision devices – Generations of night vision devices

Until now, four different generations of night vision devices have been developed. These generations also represent the historical development of the devices and their possibilities.

Generation 0

It begins with Generation 0, which is an infrared converter based on the near-focus principle. These have been known since 1940 and were used in military vehicles during the Second World War. The basis was the image converter tube AEG-Telefunken 6914, which is still used today by the German Armed Forces in the Fero51 night vision device.

Generation 1

Generation 1 uses image converter tubes based on the inverter principle and thus achieves an increase of light from 1,000 to 8,000 times. However, these devices only have a lifetime of 1,000 to a maximum of 2,000 hours. Generation 1 night vision devices usually also use infrared lamps to amplify natural IR-light.

Are you thinking of buying a pair of night vision goggles?
Check out our review of the best night vision goggles available online here.

Generation 2

A further stage of development is the Generation 2. Night vision devices of this generation use a so-called micro channel plate between the photocathode and the screen. It functions as a secondary electron multiplier. In this way, a residual light amplification of up to 20,000 times can be achieved. Generation 2 also have a much longer lifespan than Gen 1 devices. It is now between 10,000 to 15,000 hours.

Generation 3

Generation 3 is a further development of the 2nd generation devices. This generation also uses micro channel plates. However, in addition it also uses gallium arsenide (GaAs), a very sensitive chemical substance. This semiconductor material is used for the conversion of electrical signals into optical signals. In this way, a light amplification of up to 50,000 times is achieved. The lifespan of a 3rd generation night vision device is about 15,000 hours. Devices of the 3rd generation are the last devices that can currently be purchased on the open market.

Generation 4

Generation 4 night vision devices are currently exclusively reserved for the military. Here, digital signal processors are used for image processing and image optimization. These devices are not available in stores.

All night vision devices working on the principle of the residual light amplifiers cannot be used during the day. On the contrary, use in bright light can lead to damage or even destruction of the devices.

Thermal imaging devices

As already mentioned in the beginning, there is another method by which a night vision device can work. Thermal imaging devices work like a thermal imaging camera. With the help of pyroelectric or bolometer arrays (Focal Plane Array), the thermal radiation of an object is recorded and made visible. The advantage is that these devices can also be used during the day. But they also have a disadvantage, they are significantly more expensive than night vision devices that work as residual light amplifiers.

How do night vision devices work
An image obtained through a night vision device that combines infrared amplification and therman imaging. Photo: Flickr

Application areas for night vision goggles

As a private person you can only buy night vision devices of the generation 1, 2 or 3 on the open market. These devices are available in different designs – for example as night vision goggles or night vision scopes for hunting or wildlife observation.

Over the last years, night-vision paintball and other sports have gained in popularity – especially since well-functioning night vision goggles can already be bought for around 200 USD.

Check out our post on the best affordable night vision goggles here.

Furthermore, night vision devices can also be a fun toy for kids where they can learn about the science behind it while playing spy. Simple night vision devices for kids can be purchased online for less than 50 USD. Check out our overview of the best night vision goggles for kids here.

Night vision devices that make invisible infrared light visible are often also used in surveillance cameras for object protection. Mostly in combination with infrared emitters for invisible illumination.