Paul Roberts, age 13, of Dayton, Ohio, for his question:

WHAT MAKES A VAPOR LAMP WORK?

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

The first vapor lamp was made up 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 off a yellow or orange light.

Fluorescent lights are a form of vapor lamp.