I was tearing open individually-wrapped cough drops in the dark, and noticed that when I pulled apart two adhesive-joined pieces of silvery plastic film, small flashes of light were produced. It was not a reflection--it was pitch dark.
What causes this?
The product is Bee M.D. Organic Honey Throat Drops--kind of gooey, old ones (laugh). They contain menthol and eucalyptus oil. I did some more experimenting and think the the flash could actually be separating the plastic from the cough drop itself rather than pulling apart the adhesive. The item is small, the room is dark, my finger has a wound, and all in all it's hard to tell for sure.
I don't know if this is a physics or chemistry question--it depends on the answer.
Answer
Some digging revealed the answer. It's called Triboluminescence. Basically, when certain materials are subjected to mechanical shock, chemical bonds are asymmetrically broken. This creates a charge separation, which on recombination ionizes the nitrogen in the air. Resnick-Halliday-Walker (in the Electric Field chapter--its the 'chapter conundrum-) states that the nitrogen emits UV light after ionozation. This UV light is absorbed by oil of wintergreen crystals in wintergreen lifesavers, which then emit blue light. All this absorption-emission of light is due to electrons jumping energy levels.
The Examples section of the linked wiki article mentions adhesive tape, so adhesive tape must have a similar mechanism. They're rather vague on the mechanism, though.
Another mechanism I've heard of is that the nitrogen in the air attaches to the broken bonds, releasing energy. That works, too.
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