MadSci Network: Chemistry

Re: what makes light from wintergreen lifesavers

Date: Tue Dec 21 13:33:49 1999
Posted By: Arnold Anderson, Staff, Tribology/Friction systems, retired (Ford Scientific Laboratory)
Area of science: Chemistry
ID: 945537287.Ch

Kyle and Joey;

You asked why wintergreen lifesavers made light when you chewed them, but not when you sucked on them. Wint-O-Green Lifesavers(TM) emit blue light flashes when they are bitten. The light flashes are dim, so you must observe them in the dark, after your eyes are dark-adapted. The name for this form of light is triboluminescence (pronounced try-bow-loom-in-ess-ence). Luminescence refers to light that is generated without high temperatures. Tribo is from the Greek word for rubbing. This should give you a clue as to the source of your light flashes.

There are several ways that light may result from rubbing. One comes from the hot spots made by the friction of rubbing. This is called incandescence. You may have seen sparks from a grinding wheel, or even from a metal object dragging from a car or truck. Early man used frictional heating to start fires. Even if you bit down hard and fast, this would only produce an orange colored light. Your light was blue, like a spark.

Sparks are a second way light results from rubbing. You have seen many forms of this. Lightning is a grand form of this, using the friction of moving air. On a much smaller scale are the static electric sparks, in dry air, from combing your hair, or quickly rubbing some fabrics. Even rapid removal of adhesive tapes may produce visible sparks.

Some of what you saw resulted from tiny sparks as you fractured sugar crystals with your teeth. However, much of the energy in the sparks is not visible to our eyes. It is in the ultraviolet range. However, you said that you were eating Wintergreen mints. Wintergreen flavor comes from an oily chemical called methyl salicylate. This chemical, and several others, absorbs light that we cannot see, and returns it as light that we can see. Wintergreen fluoresced the blue light that you saw.

Since you have access to the Internet, you may wish to look up the following sites. They are written at the high school level. You two appear to be very bright, so you should enjoy this added information. The site of Professor Sweeting has some excellent photographs of the blue sparks, and includes some experiments that you might wish to try yourselves.

"Scientific Experiments At Home: Wintergreen Candy And Other Triboluminescent Materials" by Linda M. Sweeting

"Impurities give crystals that special glow," by C. Wu , Science News, May 17, 1997

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