I got this idea from looking at one of those fire warmers that restaurants use outside. I was wondering how hot the clear shell was and how hot the flame was. Then I wondered if a non-contact thermometer would measure the shell temperature or the fire temperature.

The thermometer is basically a camera with only one pixel sensitivity that only measures infrared. As an object gets hotter, it starts radiating more and more infrared waves. The thermometer uses the reading of its one pixel to give a temperature to the user. A laser thermometer actually also measures infrared, it just has a laser pointer to show youwhere the thermometer is measuring.

I always thought that infrared was the same as heat. Thinking about this, it obviously isn’t, as heat is molecular jiggling and infrared is less energetic light (light as in visible light, not the whole light spectrum). What infrared actually has to do with heat is not as related.

There are two main conversions that would explain their relationship to me:

Heat to infrared:

This is because things always emit radiation (unless said thing is absolute zero in temperature). Humans emit infrared, as they have some temperature. The sun also emits infrared, although it is also hot enough to emit visible light. This was never too hard for me to understand, as it makes intuitive sense.

Details: the energy kicks electrons into a higher orbital or an excited state. When the electron jumps from the excited state back to the neutral state, it radiates electromagnetic waves.

Infrared to heat:

This was more confusing for me. It makes sense for things to emit infrared, but how would a (relatively)low-energy photon give heat to other things? The answer is something similar to how a microwave heats food. A microwave oven produces microwaves, which are basically low-energy infrared waves, which bounce around in the microwave chamber. This then vibrates the water molecules, which heat the food up. Infrared works in the same way, except instead of vibrating only the water molecules, it molecularly vibrates your whole body(and other things), which heats it up.

Looking through this, I found a loophole in the system: If you pointed a non-contact thermometer at a really hot star, it could technically give a lower reading than if you pointed it at a cooler star. This is because the amount of infrared produces actually drops (maybe) because the star would produce a more energetic electromagnetic wave.

Another thing about non-contact thermometers: they actually measure things in a cone instead of a beam. This means that the laser pointer isn’t actually where the thermometer is measuring, its the center of the circle that the thermometer is measuring. It would be great if they made laser thermometers that actually measured in a beam, but the laser pointer might actually affect the reading.

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-That wall is at 10˚ - no 11˚ - no 100˚ - wait, how powerful is this laser?