Some of the Awesome Things You Can See with an Infrared Camera

Rhett Allain
7 min readAug 16, 2021
Photo: Rhett Allain. The family dog in infrared.

It wasn’t that long ago that it would be completely unrealistic for normal humans to own an infrared camera. I think it was around 2010 that I ordered an IR camera for work — it had a price of around $3000. That’s pretty pricey.

But now, there are a bunch of low price cameras. Most of them connect to your phone and cost under $200 (I’m a big fan of the FLIR One, but Seek Thermal is also nice).

OK, I want to get to the pictures (and videos) but I think we need just a very brief introduction to infrared cameras. Let’s start with light. Light is an electromagnetic wave (meaning there is an oscillating electric and magnetic field — I’ll call them EM waves). These EM waves interact differently depending on the wavelength. With a wavelength between 400 to 700 nanometers (where 1 nm = 10^-9 meters), we call this visible light since you can detect it with your human eye (assuming you are human).

What is Infrared?

For EM waves with a wavelength between 15 micrometers (μm) and 1 millimeter (mm), we call this far infrared — and this is what is detected by an infrared camera. Oh, near infrared is even shorter wavelengths. This is the region of EM spectrum that IR remotes use (but that’s not what we use for thermal images).

Blackbody Radiation

When you turn on your stove, it starts to get hot right away. If you continue to let it increase in temperature, eventually it gets so hot that it glows. It turns out that all objects radiation EM waves. The wavelength of this radiation depends on the temperature of the object.

Photo: Rhett Allain. An incandescent light bulb. The filament glows because it’s hot.

But what about a blackbody? There are two ways to see something. The most common method is for light to reflect off that object — that light then enters your eye and you can see it. The other way to see something is for the object to create its own light due to its temperature. If the thing doesn’t reflect light and only emits — that’s a blackbody.

Here’s a great simulation from PhET that shows how light changes with different temperatures.

--

--

Rhett Allain

Physics faculty, science blogger of all things geek. Technical Consultant for CBS MacGyver and MythBusters. WIRED blogger.