Jim Sharf, age 13, of Bessemer, Ala., for his question:

HOW DOES A VAPOR LAMP PRODUCE LIGHT?

A vapor lamp is a source of electric light that uses a vapor or`' gas, rather than a wire, to produce light.

The first vapor lamp consisted of a tube filled with vapor and a small pool of mercury at one end. When the tube was tipped, the mercury rolled through the gas causing it to glow.

Modern vapor lamps are rather short and stocky. They are used outdoors for street and highway lighting. A short quartz tube inside a larger glass tube causes the gas between them to glow.

Different gases give various colors. For example, sodium gives yellow or orange light.

Fluorescent lights are a form of vapor light.