Around Halloween, stores begin to sell necklaces, wands and other plastic items that glow coolly in the dark. Based on bioluminescence, they contain luciferins, and work the same way as a firefly’s glow. But, for extra sparkle, a trick or treater might also chew wintergreen Lifesavers. If you stand in the dark and crush one between your teeth, it will spill blue-green flashes of light. Certain substances (some quartzes and mica, even adhesive tape, when it is yanked off specific surfaces) are
triboluminescent; they give off light if you rub, crush, or break them. Broken wintergreen fluoresces and broken sugar gives off ultraviolet light; the combination – in candies that contain both sugar and oil of wintergreen – produces tiny bolts of blue-green lightning. Try this parlor game: Step into a closet with a mouthful of wintergreen lifesavers and a friend and wait for sparks to fly.
-- Diane Ackerman, A Natural History of the Senses