The Difference Between Thermal Night Vision and Infrared Night Vision

In the world of night vision, one of the most common points of confusion stems from the difference between thermal imaging products and digital night vision products. Companies and consumers will often use these terms, sometimes interchangeably, to describe two completely different things. 

So what is going on here? Digital night vision is obviously not the same as thermal. How can they both be called "infrared"?

To answer this question, it must be understood that the infrared spectrum is actually quite large and consists of several different categories: near infrared, short wave infrared, medium wave infrared, and long wave infrared.

Making the claim that a device uses "infrared technology" is not very specific. The behavior of the wave can be completely different depending on what part of the infrared spectrum you are looking at. Thermal devices and digital infrared devices both operate within the bounds of the same infrared spectrum. They just do it in completely different parts. 

Digital night vision devices, also sometimes called near-infrared devices, operate in the first sub-group of the broader infrared range. This category is called near-infrared (NIR) and includes the wavelengths between 750nm-1000nm. It's very similar in behavior to light.

It should be noted that this term "near-infrared" is not literally saying that a device is close to the infrared spectrum. Near-infrared is a category within the infrared spectrum and is a scientific classification. This unfortunate naming convention can cause a lot of confusion among consumers.

Thermal imagers on the other hand operate between 7000nm-15000nm. This range also happens to be exactly where much of the radiant energy present in everything (animals and objects) tends to reside. As these objects go through the natural process of atomic decay, they emit radiation which thermal imagers can see and use to construct a night vision image. 

So, to summarize the answer to this common misconception, both devices can be referred to as infrared night vision because they both operate within the bounds of the infrared range. Digital night vision devices work in the portion of the range that is extremely close to visible light. The wavelength here is much shorter. Thermal imagers, also known as heat cameras, work in the upper bounds of the infrared range. These wavelengths are much longer and coincidentally happen to match the wavelength of the natural radiant energy that is emitted by everything in the universe. 

Note. Please note that many aspects of this article, particularly the technical side, have been oversimplified for practical purposes.