William Brewer, age 12, of Pocatello, Idaho, for his question:

CAN YOU EXPLAIN LUMINESCENCE?

Luminescence is the emission of light by means other than heat. For example, fireflies give off a visible glow often called cold light.

Certain substances glow at low temperatures when they are exposed to cathode rays or X rays. Thus, non luminous radiation such as X rays can produce luminous radiation.

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.

Luminescence that lasts after the radiation is removed is called phosphorescence. Many minerals are phosphorescent.

The light given off by fireflies and certain fungi, you will be interested to know, is called bioluminescence.