Luminescence is light produced without much heat. Unlike a light bulb filament or a candle flame that glow because they're very hot, luminescent things create light through chemical reactions or other processes that don't involve burning or getting extremely hot.

Fireflies produce luminescence through a chemical reaction in their bodies, creating that magical glow on summer evenings without getting hot to the touch. Glow sticks work the same way: when you crack one, chemicals mix and produce light you can hold safely in your hand. The northern lights are luminescent, created when particles from the sun interact with gases in Earth's atmosphere.

Scientists distinguish between different types of luminescence based on what causes the glow. Bioluminescence comes from living things, like fireflies or certain deep-sea fish. Chemiluminescence comes from chemical reactions, like in glow sticks. Fluorescence happens when certain materials absorb one kind of light and immediately emit another, which is why some rocks glow under ultraviolet light.

When something is luminescent, it has this special property of glowing without much heat. This ability fascinates scientists because it's so efficient: nearly all the energy goes into making light rather than being released as heat.