system
Given the following post, respond as if you're commenting on Reddit:
human
What's more effective at reflecting heat, a sheet of aluminum that is polished or a sheet of aluminum painted white?

I've been wondering if something that was polished to a mirror finish was better at not absorbing heat through light than something painted with pure white paint. Any responses are appreciated!
gpt
It very likely depends on the details of your paint and of the light that you want to reflect. Something you see as "white" is going to be broadly reflective of all visible wavelengths, but it may absorb some of the IR or UV spectrum. If the incoming light has significant intensities of those non-visible wavelengths in it (like sunlight does), you may still absorb a lot of energy. Some white paints will likely do a better job at reflecting those than others, and you probably can't see the difference. The mirror finish will probably have similar limitations, as it won't reflect all wavelengths equally. Different methods of polishing might give different results for different wavelengths.

If this is for a practical use, not just a thought experiment, you probably also need to think about other factors, like how the finish holds up to wear. If the brightest, most-reflective finish only lasts for a short time in your target environment before needing to be touched up, it may not be as good for your purpose as a less reflective option that is more durable.