The Reactor Electromagnetic HID Ballast is the simplest, smallest, most efficient and most economical type of electromagnetic ballast. The reactor ballast is electrically in series with the lamp. There is no capacitor involved with the operation of the lamp. Because of that, the lamp current crest factor is desirably low, in the 1.4 to 1.5 range. Reactor ballasts feature a simple design, which uses the Line Voltage to ignite the lamp. Reactors are generally used as Normal Power Factor devices. Their highest current draw occurs during starting, which must be allowed for in the capacity of the line. The line current can be lowered by using a capacitor across the line to achieve a High Power Factor of over 90 percent allowing more ballasts per circuit. This ballasts requires an ignitor to start the lamp.
The Reactor ballasts limit the number of fixtures that can be used on a circuit because they draw substantially more current during lamp starting (warm-up) and/or open-circuit operation (burned-out or missing lamp), than when the lamp is operating normally.