The Difference Between Thermal Night Vision and Infrared Night Vision
In the world of night vision, one of the most common points of confusion is the difference between thermal and infrared devices. Seemingly interchangeably, consumers frequently refer to both of these as infrared night vision — yet anyone who has used them will know that they work in completely different ways.
So how does this make any sense? Aren't they two completely different technologies? How can they both have the same name?
To answer this question, it must be understood that the infrared spectrum, which is a subsection of the broader electromagnetic spectrum, is actually quite large and has to be broken down into four smaller categories: near infrared, short wave infrared, medium wave infrared, and long wave infrared.
Thermal devices and infrared devices both operate within the bounds of the infrared spectrum. They just do it in completely different parts. As you can see in the graph above, the behavior of the wave is completely different depending on what part of the infrared spectrum you are looking at.
Digital night vision devices operate in the near-infrared sub-group of the infrared range. This is generally considered to include the wavelengths between 750nm-1000nm and behaves very similarly to light.
Thermal imagers on the other hand operate between 7000nm-15000nm. Coincidentally, this range also happens to be exactly where much of the radiant infrared energy present in all humans and animals happens to also exist.
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, also known as near-infrared night vision devices, work in the portion of the range that is extremely close to visible light. These wavelengths are 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 all organisms.
Note. Please note that many aspects of this article, particularly the technical side, have been oversimplified for practical purposes.