CHARLES D. WINTERS / SCIENCE PHOTO LIBRARY CHARLES D. WINTERS / SCIENCE PHOTO LIBRARY
Chemiluminescence. View of three different colours of "light tubes" displaying chemiluminescence. These tubes glow because a chemical reaction is taking place. At rest, the tubes contain two chemicals separated by a brittle barrier. When the tubes are shaken, the barrier breaks, and the chemicals mix and react. Like the emission of heat, emission of light is one way of releasing energy during a chemical reaction. Photons of light are produced when excited electrons inside atoms change from a high-energy orbit to a low- energy orbit. Luminescence is the emission of light for any reason other than a rise in temperature.
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