Lamp Ballasts, LED Drivers and Transformers

Match the lamp type, lamp count and wattage

A ballast is built for one lamp family and the wattages printed on its label. A ballast for 32 W T8 lamps usually will not run T5 or T12 tubes, and the label also states how many lamps it drives, such as 2 or 4. Read the existing ballast label for the lamp code, for example F32T8 or F28T5, and the number of lamps. Magnetic ballasts are older and heavier; electronic ones run lamps with less flicker and heat and are the usual replacement.

Input voltage and ballast factor come next. Labels such as 120-277 V mean the ballast accepts a range of supply voltages, while 120 V or 277 V only fits one. Ballast factor describes light output relative to a reference: low, normal and high factors trade brightness against lamp life and energy use. Dimming ballasts need a compatible dimmer, and refrigeration or cold-weather ballasts carry a low-temperature starting rating.

LED drivers and halogen transformers

LED drivers are the LED equivalent of a ballast, and they come in two types. A constant-voltage driver, such as a 12 V 25 W unit, powers strips and modules designed for that voltage; a constant-current driver feeds an LED array at its rated current, so match that current and the driver's voltage range to the array. Size a constant-voltage driver above the load, since a 25 W driver should carry well under 25 W of LEDs. Halogen low-voltage lamps often use an electronic transformer that is rated for a minimum and maximum load, and an under-loaded transformer may flicker or fail to start.

Questions about Lamp Ballasts, LED Drivers and Transformers

How do I know which ballast my fluorescent fixture needs?

Read the label on the old ballast or inside the fixture for the lamp type (T8, T5 or T12), the lamp count and the supply voltage. Replace like for like, or choose a ballast whose label lists that exact lamp. Switch off at the breaker before opening the fixture.

Can I replace a fluorescent ballast with an LED driver?

Not directly. An LED driver is not a drop-in for a fluorescent ballast. Tube-style LED lamps either work with the existing ballast, need it bypassed, or have their own driver, so read the lamp's instructions, as they differ by product type.

Why does my fluorescent light flicker or hum?

A failing ballast is a common cause, especially in older magnetic ballasts that hum. Flicker can also come from a worn lamp, a loose lamp pin or the wrong lamp for the ballast. Replace the lamp first, then the ballast if the problem remains.