Incandescence is light from heat energy. If you heat something to a high enough temperature, it will begin to glow. When an electric stove’s heater or metal in a flame begin to glow “red hot”, that is incandescence. When the tungsten filament of an ordinary incandescent light bulb is heated still hotter, it glows brightly “white hot” by the same means. The sun and stars glow by incandescence.
Luminescence is “cold light” that can be emitted at normal and lower temperatures. In luminescence, some energy source kicks an electron of an atom out of its lowest energy “ground” state into a higher energy “excited” state; then the electron returns the energy in the form of light so it can fall back to its “ground” state. With few exceptions, the excitation energy is always greater than the energy (wavelength, color) of the emitted light.
If you lift a rock, your muscles are supplying energy to raise the rock to a higher-energy position. If you then drop the rock, the energy you supplied is released, some of it in the form of sound, as it drops back to its original low-energy position. It is somewhat the same with luminescence, with electrical attraction replacing gravity, the atomic nucleus replacing the earth, an electron replacing the rock, and light replacing the sound.
Common Varieties of Luminescence in Minerals
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