system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does 'glow-in-the-dark' work exactly?

I'm sitting here sleeping at a family member's house in the Seattle area and there's a big blackout in my town. The room I'm in has those stars that stick to your ceiling and glow when you shut the lights off. How does this work exactly? Additionally, I've noticed from past experience that using a blacklight as the light source really intensifies their glow. How come?
gpt
Incoming photons, which are a form of energy, are absorbed by molecules of (usually) zinc sulphide. This energy pushes an electron in one of the atoms into a higher energy orbit (state would be a better word, since electrons don't actually orbit). It's not happy there, and will eventually fall back, at some random time in the future, and the energy released as it falls back comes out as another photon - which is light.

To start with, there are lots of energised electrons in the material, so there are lots of chances for some to fall back, so the glow is bright. As they fall back, there are fewer and fewer ready to jump, so the glow gets dimmer and dimmer.

UV has a much higher energy per photon (which is why it burns your skin when you get sunburn) so it's able to bang a lot more electrons up into higher states, so there's more energy stored, so the glow is brighter as it's released.