Luminescence produced by heating a solid substance — light emitted when heating releases electrons and holes trapped in crystal defects, causing emission of photons as they recombine. Thermoluminescence finds a distinctive food application: detecting irradiated foods. Irradiation traps charge in the mineral debris of spices, herbs, and seasonings; reheating the isolated minerals in the laboratory releases a glow proportional to the radiation dose received. This thermoluminescence test is an officially recognized method for identifying irradiated ingredients, supporting labelling enforcement where irradiation must be declared to consumers.