Ammara Khan, via facebook asked:
How do things emit light by giving off photons? Do they produce new photons or just release photons that were already there? If the photon were already there, then why doesn't everything emit its own light instead of just reflecting light?
Chris - What they're doing is using a chemical reaction to excite a molecule. When you excite a molecule, you give some energy to the electrons that orbit around that molecule in the atoms. Those electrons get kicked up to a higher energy state temporarily, and they then lose the excess energy again by falling to their original starting position, and the energy that they lose, they give out as a photon of light. So that's how you then spit out light if you're an organism that glows underwater like a jelly fish for example.