Space, Physics, and Math

Why do wintergreen candies spark in the dark?

- Asks Gaurav from Washington, DC

May 19, 2008

Turn up your sound and click on the VIDEO above to see a lifesaver sparking away.

It’s a hot night in the Adirondack mountains, crickets are playing their evening sonata and I’m watching cool-blue sparks in the dark. Four tweens in their bunk beds have now independently confirmed what two minutes ago was just a rumor to us: Wint-O-Green Life Savers spark in the dark. And it’s awesome.

So what causes the cool light show? When you crunch down on a candy, you shatter its sugar crystals. (Chemists define a solid crystal as a substance where each unit of matter repeats with a regular pattern. Think: salt or diamond) Scientists believe that the structure of a crystal determines whether or not it will emit light when broken, a phenomenon dubbed triboluminescence.

Crystals in which every unit is symmetrically arranged around a center point don’t tend to have this feature. But crystals that don’t have this symmetry or are impure often do. This second class includes sugar. When you break a sugar crystal, one half of the crystal ends up with more electrons than the other. The electrons leap across the gap to the more positively charged side. “There is a little bolt of lightning that shoots between the faces,” says Arnold Rheingold, a professor of chemistry at the University of California, San Diego who has studied triboluminescence. (Recent research suggests that the sparks’ energy is powerful enough to trigger chemical reactions such as combustion.)

In your mouth, these jumping electrons crash into nitrogen atoms, which is abundant in the air. The nitrogen briefly absorbs the energy from the collision and then spits out some energy — in the form of ultraviolet light.

So far, all of this could happen with many hard, sugary candies. But we humans can’t see ultraviolet light. What bumps certain sweet suckers into the world of blue, visible lightning is their flavoring. Wintergreen oil (or, in the case of the ones I just tried staring into the bathroom mirror in the dark, “artificial flavor”) will absorb the energy from the ultraviolet light and then emit blue light.

So next time you’re focused on freshening your breath with a wintergreen treat, find a dark space and a mirror and let the lightning fly.

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About the Author

Susannah Locke holds a B.S. from Haverford College, where she studied molecular biology and psychology and ran the college’s literary magazine. For two years following graduation she played with neurons as a research technician at the University of Pennsylvania and The Children’s Hospital of Philadelphia. After using almost every type of test tube on the market for every conceivable purpose, she removed her gloves to become a journalist and improve the public’s understanding of science.

Discussion

5 Comments

Doris says:

I am amazed at what you have discovered!

Liz Schrock says:

Cool! Something to add to the “tornado emergency kit”! thanks

ali says:

Dude! I always thought it was a myth! Sweet video!

Dave says:

The same thing happens when peeling apart the paper wrappers for band-aids or nasal strips.

Rajarshi says:

I wish i could have such one!!! great way to trick my mates!!

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