When some object gives off light, that light is called luminescence. The luminescence of a lighthouse helps keep boats safe on foggy nights.
Glow-in-the-dark stars stuck to your bedroom ceiling have a luminescence you can see when you turn out the light at night, and lightning bugs blink on and off with luminescence in the summertime. Luminescence, scientifically speaking, describes a glow or light that's emitted at a cool temperature, rather than one caused by a fire, for example. The Latin root is lumen, or "light."