Eli5: how do thermal cameras capture heat without any physical contact
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Just as a not to you, OP, I’ve seen more than one comment say something like “heat is infrared light.” When you read that, you should envision it the same way we say “time is money.” You can’t actually transfer 20 minutes off your lifespan to the butcher in exchange for a steak. Heat IS the average motion of the individual atoms of a substance. The onlynthi ga that don’t jiggle around just a little bit are things at absolute 0 with no thermal energy. But since nothing can reach absolute 0 then all things have thermal energy. And along with thermal energy comes light. Not necessarily visible light, but all matter above absolute 0 emits photons. The hotter something is, the higher energy the photons it emits are. Higher energy photons have a shorter wavelength. If you have something really really cold, it can emit radio waves. If it’s really really reeeeeally hot, it emits gamma rays.
Almost everything we deal with in our day do day life is just in the range of temperature that emits infrared light. You know that if it heats up above a few hundred degrees it will start emitting visible light. The sun is hot enough that it emits UV light. But since most things we deal with are infrared light, then an infrared camera can tell which things are hotter than others. In fact, a normal camera can too. If you point it at two blocks of metal and one is glowing red, that’s the hotter one. But since most things emit light that is outside the range a regular camera can detect, the information is limited. Actually, the information you can get from an infrared camera is also limited by the wavelengths of light it is designed to detect. Things that are too hot or too cold won’t show up on them either.
Edit: oh, and an infrared camera can’t tell the difference between something emitting IR light because it’s in the correct temperature zone or if it’s designed to emit light like the IR LED on the end of your TV remote. The same way your camera can’t tell the difference between something emitting red light like an LED or if it’s red hot. You usually can tell the difference with context, but the camera only sees red.
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