A ballast is a device used with electric discharge lamps to make them operate properly. A ballast has two purposes. To start a lamp it provides the high voltage needed to cause an arc to jump from one end of the lamp to the other. Once an arc is established, the ballast allows the lamp to continue to operate by providing the proper, reduced current flow to the lamp.

Electric discharge

The electrons orbiting atoms of the gas inside an electric discharge lamp are at certain fixed energy levels. The energy level of the orbiting electrons is raised when the traveling electrons of an arc collide with them and give up some energy. The orbiting electrons are not stable at the higher energy level and drop back to their original level. In doing so each electron gives up a photon of energy which is emitted as light.


The elements which serve as halogen gases are usually iodine or bromine.


The powder coating in an electric discharge lamp is the phosphor. The most common chemical used to make white light is calcium halophosphate. Other colors are produced by a variety of other chemicals.


Tungsten is a metal with a high resistance to the flow of electricity and a melting temperature of 6120 degrees Fahrenheit. It is often used in incandescent lamp filaments because its resistance will cause heat to be generated until it glows white. It can maintain this glow since its melting temperature is so high.

To return to the Table of Contents click TABLE OF CONTENTS