Triboluminescence
Triboluminescence is a flash of light that happens when you crush or break certain materials.
Think of it this way
Crush a sugar cube with pliers in a dark room. As the crystals crack, you see a brief flash of light. The breaking pulls the sugar apart and lets out stored power as a glow. That flash from the cracking is triboluminescence.
Explaining triboluminescence by grade level
Some candy gives off light when you bite it. The hard candy breaks apart in your mouth. That snap makes a tiny flash. You can see it in the dark.