During a sunny day the walls of my house warm up (no surprise). My question: how much of this warming up (if any) comes from visible light? I associate infrared with thermal energy. If my house was floating in space (to prevent any thermal exchange with its surroundings) and I installed a giant infrared (and UV) filter between it and the sun, would it still warm up (compared to its rest temperature in full darkness)?
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3 Answers
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Yes, it would, though not as quickly as if you were getting the full spectrum of sunlight. All frequencies of the light spectrum carry energy, so it becomes a question of how much of that energy is absorbed by the house.
For example, if your house was completely black, all that visible light energy would be absorbed by the house and converted into heat. If it was completely white (or massively reflective), there would be almost no heat transfer whatsoever.
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$\begingroup$ Interesting example: certain fabric cleaners make clothes appear "whiter-than-white" by leaving chemical residue on clothes that absorbs uv rays and emits visible light. This is similar to absorbing visible light and emitting infrared (heat). $\endgroup$ Commented May 4, 2016 at 23:39
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2$\begingroup$ Some misc point. Black is the best absorbing colour for our natural spectrum of light. For different spectra the best absorbing colour could be different from black. $\endgroup$ Commented May 5, 2016 at 3:14
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To add to the answers so far, here's a outline of a pretty crude calculation you could do.
Let's assume the house is in space. That way, we won't have to worry about the other parts of the Earth equilibriating with the house. Now let's assume your house is a perfect blackbody (which may or may not be a good approximation depending on how your house is painted.) Also assume the Sun is a blackbody as well. Then if the house-sun system is in equilibrium, the energy emitted by the Sun that strikes and is absorbed by the house will also be emitted in the form of blackbody radiation. Using the Stefan Boltzmann law, you could calculate the temperature of the house. If you put filters in, you'll need to use Planck's law and some calculus.
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Yes. All matter that interacts with light absorbs it to some degree. This is true whether you're discussing UV or infrared or visible light. For example, the earth wouldn't be nearly as warm as it is if it didn't absorb visible light.
