I have an LED monitor that I use for working from home, and I've noticed that after 4 or 5 hours straight it looks darker. I turn off the computer for a while and it goes back to normal. Is this a physics thing or something that gets damaged over time?
Most likely it's automatic thermal dimming - that's how most LED monitors work to protect themselves from overheating! When the panel has been on for hours, it heats up and the monitor reduces brightness on its own as a safety measure, which is why it gets darker. When you turn it off and let it cool down, it gets back to normal brightness. Nothing's actually getting damaged, it's just a protection mechanism, though if it really bothers you, you could check that the area around your monitor has good ventilation so it doesn't heat up as much.
It's almost certainly that your monitor has a thermal protection system that reduces brightness when it gets too hot, which is completely normal and doesn't mean it's getting damaged. If it bothers you, you can try improving ventilation around the monitor or check in the power settings to see if there's some "eco" mode or power-saving feature that's automatically lowering the brightness.
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