How to Choose a Light Ballast

So, what is a light ballast? A light ballast, which is sometimes referred to as control gear, is an essential component of certain types of light fixtures, including HID (high-density discharge), fluorescent and some LED (light emitting diode) lights. If you’ve ever turned on a fluorescent light fixture and heard a low hum or buzz, this is the sound of the ballast switching on.

The purpose of a ballast is to regulate the current that flows through the bulb (sometimes referred to as a lamp). Your home’s main power supply provides a much higher current than is needed to power certain types of bulbs, so a ballast lowers the current to the optimal operating level. Also, some lamps require a greater current at the time they are switched on and shortly thereafter, and a lower current after they have been operating for a while. Some ballasts can also be used in combination with a dimmer, allowing the brightness to be adjusted for HID and florescent bulbs.

There are two types of fluorescent light ballasts: magnetic and electronic. However, magnetic ballasts are no longer manufactured as the technology has been replaced by electronic ballasts, so you’ll mostly see a magnetic ballast on older lamps.

Electronic ballasts employ a more advanced technology to regulate the current flowing through florescent bulbs. They’re also smaller than magnetic ballasts and operate at a greater level of efficiency, which allows them to produce light with less flickering and noise.

In terms of startup method, there are two types of electrical ballasts sold today: instant start and programmed start.

• Instant-start Ballasts: These start up instantaneously without pre-heating the electrodes in the bulb by delivering a high-voltage burst of electricity that lights the filaments and gas inside. This design saves quite a bit of energy overall, but the initial electrical surge can wear on the bulb filaments over time, shortening the lifespan of the bulb. This factor makes instant-start ballasts better suited for commercial or industrial installations where the light fixtures won’t be switched on and off frequently throughout the day.
• Programmed-start Ballasts: These start up using a constant low-voltage current to keep the electrodes preheated. When the light turns on, a higher voltage current is employed. This ballast design is not as energy efficient as the instant-start variety, but it does prolong the life of the lamp, making it a better choice for installations where the lights will be switched on and off many times a day, for example with lights that have motion-activated sensors.

If you notice any of the above warning signs that you may need a ballast replacement, you can test the ballast using a multimeter, a useful tool that measures electrical current. See Choose the Best Electrical Testers and Meters for help choosing a multimeter.

Although the instructions for testing a ballast may vary slightly depending on the type and your multimeter, here is a general overview for testing a ballast.

1. Turn off the power to the lighting fixture at the breaker box, then remove the casing and the bulb.
2. Disconnect the ballast and examine it carefully. If you notice any burn marks, you should replace the ballast.
3. If the ballast doesn’t appear to be damaged, follow the manufacturer’s instructions for your multimeter to test the wiring. This will involve touching the multimeter probes to certain wires to see if a current can flow through. For more information, see How Do I Use a Multimeter? If no current is detected, it’s time to replace the ballast.