Fluorescence is one of many forms of luminescence, the emission of light not resulting from heat. This distinguishes luminescence from incandescence, which is light emitted by a substance as a result of heating. All luminescence requires some input of energy to cause the light emission, and the varieties are distinguished by where that energy comes from. Note that there are several different schemes for classification of the types of luminescence and the format presented below is not absolute.
– ‘Traditional’ filament-type light bulbs work by incandescence. That’s why they get so hot.
– Fluorescent lights, including both the long tubes in many buildings and the spiral compact fluorescents that replace the traditional bulbs, work by a combination of electroluminescence and fluorescence. An electric discharge passes through mercury gas vapor inside the tube, producing strong emissions at very specific wavelengths, with the main energy in the ultraviolet. The inside of the glass is coated with a material called a phosphor that absorbs the ultraviolet and re-emits it as broadband visible light by – you guessed it – fluorescence. By changing the composition of the phosphor you get ‘warm white’, ‘cool white’, etc.
– Light-emitting diodes (LEDs) work by electroluminescene, with an current passing through a semiconductor material.
– There are many bioluminescent organisms that produce their own light for mating, prey avoidance, counterillumination, communication, and other purposes. Fireflies are a well-known example on land. Bioluminescence is found very widely in the ocean, both near the surface in plankton, and in many deep sea critters. Check out the Bioluminescence Web Page at UC Santa Barbara.
– Glow-in-the-dark materials, like the plastic stars in kids’ rooms, work by phosphorescence, absorbing energy while they are exposed to light and releasing it over time.
– You rarely see it now, but radioluminescence used to be commonly used to make things like instrument displays and clock or wristwatch hands glow steadily in the dark. You can’t use phosphorescence for that since the stored energy would fade out too quickly. The items that you wanted to glow were painted with a mixture of radium, a radioactive substance, and a phosphor. The particles emitted by the radium would strike the phosphor, producing a continuous glow. We know more about the harmful effects of radiation now, so these have largely disappeared.
You can find more information on all of these forms of luminescence on Wikipedia or with general web searches.