(YouTube) Science of Glowing Mushrooms. Posted 6/20/2013. Good explanation of how light is emitted from the chemical reaction. That is, an electron is excited and put in a "higher" orbit, then when it falls back to its (normal) lower orbit it emits a photon.
Fireflies: Torchbearers Of The Insect World. The torches of these insects have been used by humans for some practical purposes. For instance, the medical doctor William Gorgas once was operating on a wounded soldier in Cuba during the Spanish-American War when the lights went out. Dr. Gorgas was able to finish the operation using the light of fireflies, called cucuyos in Spanish.