Luminescent means giving off light without much heat, or giving off a soft, gentle glow. When something is luminescent, it produces its own light through a chemical or biological process rather than mainly by burning or getting hot like a lightbulb filament.

Fireflies are luminescent: they create a cool, greenish glow in their bodies through a chemical reaction, lighting up summer nights without generating much heat. Deep-sea creatures like anglerfish use luminescent lures to attract prey in the dark ocean. Glow sticks become luminescent when you crack them and mix the chemicals inside, creating that distinctive cold light that lasts for hours.

Scientists distinguish luminescent light from the light produced by things that get hot. A candle flame usually isn't called luminescent because it produces light mostly through heat and burning. But a luminescent jellyfish glowing in dark water or luminescent paint on a watch dial produces light through different processes.

You might describe something as having a luminescent quality when it seems to glow softly, even if it's not literally producing light. The luminescent quality of certain clouds at sunset, or the luminescent appearance of some minerals under special lights, captures that sense of mysterious, beautiful glowing.