We asked what substance in Wint-O-Green Life Savers makes this particular brand and flavor of candy more prone to triboluminescence, the creation of light by friction, often associated with crushing, scratching, or—in this case—chewing solid objects.
It's all a matter of taste. The methyl salicylate flavoring—otherwise known as oil of wintergreen—is the culprit behind the Wint-O-Green Life Saver's comparatively unusual triboluminescence.
Life Savers are made of crystalline sugar, the structure of which is shattered when the candy is chewed. When the sugar crystals break, some molecules are left ragged or incomplete, freeing some electrons, which then need a place to go. These electrons collide with nitrogen molecules in the atmosphere and impart to the nitrogen excess energy. The nitrogen, wanting no part of that energy, converts it to light.
Normally, the majority of this nitrogen-emitted light falls into the ultraviolet range, so only a small percentage of the total energy shed shows up as visible light. But the methyl salicylate in Wint-O-Green Life Savers alters this equation. It functions like a phosphor in a fluorescent light, absorbing the shorter wavelength ultraviolet photons and converting them into higher wavelength visible photons.
Specifically, oil of wintergreen converts UV into blue visible light, which accounts for the characteristic blue sparks emitted when you chew Wint-O-Green Life Savers.