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Why can crushing sugar crystals produce tiny flashes of light?
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luminescence
Figure 1: Energy levels of a luminescent centre (see text).
The phenomenon where crushing sugar crystals produces tiny flashes of light is known as triboluminescence, which is luminescence caused by friction or mechanical action.12
When these crystals are crushed, the mechanical separation of their surfaces generates positive and negative electric charges. This separation creates an electric discharge, which results in the emission of light. In some cases, this light is produced by the excitation of surrounding air molecules by the electric discharge. This process is not unique to sugar; it has been observed in many other organic and inorganic substances, as well as during the crystallization of certain salts from hot solutions.1