Angie Sutter, age 13, of Casper, Wyo., for her question:

WHAT IS LUMINESCENCE?

Luminescence is the emission of light by means other than heat.

Some butterflies give off a visible glow called cold light. This is a type of luminescence, as is the glow caused when certain substances are exposed to cathode rays or X rays.

Luminescence that continues only as long as the radiation is applied is called fluorescence. In a fluorescent lamp, invisible ultraviolet rays bombard a phosphor coating to produce light. Thus, luminescence that lasts after the source of the rays is removed is called phosphorescence. Many materials are have this quality.

The light given off by a butterfly and certain fungi is called bioluminescence.