Ballasts: 5 of 21

The original fluorescent system, developed in 1939, was a preheat system. In preheat systems, the current flows through a separate starter switch that, when closed, preheats the cathodes for one to two seconds. Then, the starter switch opens and the voltage is applied across the bulb to start the lamp.

Preheat lamps are the least common type in use today, although you will still find them in small applications such as cabinet, display case, and emergency lighting. Preheat circuits, however, are fairly common in some plug-in fluorescent lamps.

The major disadvantage of this type of lamp is the time it requires for preheating, and therefore for starting.

Preheat lamps, however, offer some advantages such as low initial cost and relatively long lamp life.

Preheat systems typically use electromagnetic ballasts.