HOW COME?: Rubbing materials create light

Call it the Electric Lifesaver Effect: As with rubbing two sticks together to create a flame, light can be made when certain materials are rubbed together, ripped apart, scratched or smashed to bits. But the light isn't coming from a fiery flame. Instead, friction produced in the materials (such as adhesive tape, or Wint O Green Life Savers) triggers a burst of static electricity. And as with touching a metal doorknob in a (dry) dark room, we see a blue spark flash.

The technical term for the effect is "triboluminescence," from a Greek word meaning "to rub" and a Latin word meaning "light." Any sugary hard candy can give off triboluminescent sparks, but the light from Wint O Green Life Savers is easiest to see.

How does it work? Sugar crystals are naturally asymmetrical, so they tend to break apart in a lopsided way. When such crystals fracture, electric charges in the molecules separate, and negative electrons are split off from positive protons. The sparks fly when the charges reconnect.

Like regular lightning, mini-lightning occurs when the electric current excites nitrogen molecules in the air. The nitrogen molecule emit photons of light, mostly in the invisible-to-us ultraviolet range. So even in the dark, the visible sugar sparks are hard to see.

That's where the flavoring in Wint O Green Life Savers comes in handy. If you and a friend take turns chomping down on wintergreen candy in a dark room, you should see sparks fly from your friend's open mouth. Wintergreen oil (methyl salicylate) is a naturally fluorescent compound. The minty oil absorbs high-energy, short-wavelength light, re-emitting lower-energy, longer-wavelength light. So wintergreen helpfully absorbs the ultraviolet light made by the nitrogen molecules in the air of your mouth, while punching up the visible light. The result: You see a flood of extra-bright blue light.

(To save your teeth, use a pair of pliers to create candy sparks. Stay in a dark room for at least 10 minutes, so that your eyes get accustomed to the dark. Then, use the pliers to crush your Wint O Green Life Savers, making sparks fly.)

The same phenomenon can cause flashes of light from adhesive tape. Take two pieces of duct tape and press the adhesive sides together, leaving a few inches free at one end. Now, go back into your dark room for a bit -- and then let 'er rip.

When you quickly pull apart the strips, you should a glowing line of blue light where the strips separated. You can also try regular Scotch tape, simply ripping it off the roll. Even self-stick envelopes will sometimes glow when you open them quickly in the dark.