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    Light on a Stick

    Kids, you have probably seen a Light Stick, a plastic tube that is often stored in an emergency survival kit instead of a flashlight. Once activated, the Light Stick glows brightly for many hours. Did you ever wonder how it can do this? The process is called chemiluminescence. Fireflies and light sticks make "cold light" from this chemical reaction that makes light without making any heat

    The "cold light" given off by living things is called bioluminescence. Certain kinds of moss glow in the dark, and rotting tree stumps give off an eerie light that is called foxfire. Many cases depend on bacteria. The flashlight fish, for example, lives very deep in the ocean where it is absolutely dark. They have sacs of luminous bacteria near their eyes. The bacteria glow all the time, but the fish can cover and uncover the sacs with flaps of skin. They search for food with these lights, blink to attract other flashlight fish, and confuse their predators by flashing and then quickly changing direction.

    Bacteria and fireflies make their cold light by mixing chemicals called luciferin, luciferase, oxygen, and ATP (adenosine triphosphate). This reaction has even been developed into a sophisticated medical test for treating tuberculosis (TB). Saliva samples taken from TB patients are treated to make luciferase and then luciferin is added to make them all glow. Each sample is then exposed to a different antibiotic until the right one works, the bacteria are killed, and the glow goes out.

    In Light Sticks, a large outer tube is made of flexible, translucent plastic. Inside is a solution of oxalate ester and fluorescent dye molecules. Also inside is a smaller glass tube that contains hydrogen peroxide. When you bend the stick, the thin glass tube breaks and allows all of the chemicals to mix and react. This chemical reaction provides the energy needed by the real workers in this process, which are called electrons. It is the Light Stick chemical system that has been repackaged to also make glowing bracelets, necklaces, and earrings. So now you know a little bit about the science behind the bright lights that your parents might make you wear at outdoor sporting events, concerts and fireworks!

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    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    [email protected]
    June 1996

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    Reference: October 1995 issue ofChemMatters, a publication of the American Chemical Society, 1155 16th St., N.W., Washington, DC 20036.