system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does a high speed fan appear as if it is rotating in some distinct frames to human eye?
gpt
This is because almost all lights we use have some flicker. The lights are powered by 50 or 60 Hz mains, and so will often flash (or at least change brightness and olor) with each half-wave, so at 100 or 120 Hz. High quality LED or compact fluorescent use switch mode power supplies, which filter out the mains flicker, but they run at some thousands of hertz, and so flicker at that rate.