Night Vision Devices vs. Thermal Imaging: Key Differences and How to Choose

A person is standing at the edge of a field about 150 yards away from you. The night is moonless, and behind him there is a dark strip of forest.

Look through a good night vision device, and a fairly recognizable scene will appear before you: grass, trees, a fence, a human figure. The world has lost its familiar colors, but it has remained the world. You only need to look carefully.

Now pick up a thermal imager.

The picture changes completely. Many background details become less expressive, while the person may immediately stand out as a bright silhouette against the colder vegetation. You notice him almost instantly — although you may see fewer details of his clothing, face, and the surrounding environment.

This, in fact, is the main practical difference between the two technologies.

Night vision optics helps you see the surrounding scene better in insufficient light. Thermal imaging shows the differences in the thermal infrared radiation of objects.

A Thermal Imager

Any object emits thermal radiation.

A person emits it.

A tree emits it.

A stone, a car, the roof of a shed, and a cup of coffee do as well.

We simply do not see a considerable part of this information with our eyes.

A thermal imaging system makes it visible.

For the operation and adaptation of such systems, an entire category of equipment and thermal imaging accessories is used. But the main secret of these devices lies in the lens.

The point is that the thermal radiation needed by a thermal imager will not properly pass through an ordinary glass lens.

That is why thermal optics uses special materials capable of transmitting and focusing photons of the required wavelength. One of the best known is germanium. Special chalcogenide glasses and other IR-transparent materials are also used.

This partly explains the rather considerable price of good thermal imaging optics.

A Night Vision Device

When the sun goes down, light does not disappear with the click of a switch. Even far from the city, there are still stars, the Moon, atmospheric glow, and distant artificial light sources. Light reflects from the ground, trees, buildings, and people — there is simply too little of it for our eyes.

Classic night vision takes this scarce light and amplifies it. And if there is practically nothing to amplify, a different approach becomes necessary.

Modern digital night vision systems often use infrared illumination. Essentially, it is a flashlight whose light the human eye cannot see. It directs infrared radiation onto the scene. Objects reflect it, the device’s sensor records the reflected signal, and the user receives an image even where natural illumination is absent.

So Which One Is Better?

Neither night vision nor thermal imaging can be called the universal winner.

The choice of the device depends on the task.

If you need to navigate in the dark and see the surrounding world in its usual detailed form, distinguish the road, objects, and terrain — night vision has obvious advantages.

If, however, you need to quickly detect a person or an animal in complete darkness or against a visually complicated background, a thermal binocular usually proves to be the preferable choice.

When observing wildlife, a thermal imager helps find an animal that the eye could easily miss.

During search and rescue operations, temperature contrast can point to a person where an ordinary camera provides too little information.

What If They Are Combined?

The logical continuation of development has become hybrid observation systems. In such devices, the thermal imaging sensor works as a means of primary detection. It quickly highlights an object against the terrain regardless of the lighting level.

After that, the user can switch to the night vision channel to evaluate vegetation, obstacles, and other details that the thermal imager transmits much worse. In some models, both images can be overlaid on one another, combining thermal information with the familiar visual picture.

Image by withplex (pixabay.com)