How to Find the Right Fluorescent Ballast (and When to Skip It)
Updated October 2026.
Every fluorescent lamp needs a ballast. It supplies the voltage spike that strikes the lamp, then limits the current so the lamp doesn't destroy itself. Screw-in CFLs hide the ballast in the base; tubes and pin-base CFLs use a separate ballast inside the fixture. When that ballast fails, matching the replacement comes down to what's printed on the old one.
Is it the ballast or the lamp?
Before you buy anything, rule out the cheap fix. Turn off power at the breaker and put lamps you know are good into the fixture. If it still won't light, the ballast is the likely culprit. Common ballast failure signs:
- Lamps won't start, or start slowly, even with new tubes
- Flickering or a loud hum that new lamps don't fix
- Dark or burned ends on lamps that are fairly new
- A swollen or leaking ballast case, or a burning smell
Also check the sockets (tombstones). Cracked or loose sockets cause the same symptoms and cost a few dollars.
The six things to match on the old label
- Lamp type and wattage. The label lists the lamps it runs, such as F32T8 (32 watts, T8, 1 inch diameter) or F54T5HO. A T8 ballast will not run T12 or T5 lamps.
- Number of lamps. One, two, three or four. Many multi-lamp ballasts also run fewer lamps or shorter lengths of the same family; the label lists every combination it supports.
- Input voltage. 120V, 277V, or universal 120-277V. Universal ballasts cover both and simplify stocking for buildings with mixed circuits. Also look for 347V or 480V on the label. Warehouses and industrial buildings sometimes run lighting at 480V, often with HO (high output) lamps, and 347V is the standard lighting voltage in Canada. Those fixtures need a ballast rated for that voltage, such as a 347-480V T5HO ballast. A 120-277V ballast will fail on them.
-
Starting method.
- Instant start strikes the lamp immediately with no preheat. It is the most efficient and the most common, but frequent switching shortens lamp life.
- Programmed start preheats the lamp ends before striking. Use it where occupancy sensors switch lights on and off many times a day.
- Rapid start heats the lamp ends while starting. It is mostly found on older and magnetic ballasts.
- Ballast factor. Low (around 0.77), normal (around 0.88) or high (1.0 and up). Higher ballast factor means more light and more watts. Match the old one unless you want to change light levels.
- Size and wiring. Most replacements share a standard footprint, but check the length and mounting holes. Wire to the diagram printed on the new ballast, not the old one.
Magnetic vs electronic
Magnetic ballasts are heavy, hum, and make lamps flicker on startup. Federal efficiency rules ended production of most magnetic fluorescent ballasts years ago, so if your fixture has one, especially with T12 lamps, the replacement will be electronic and may require different lamps. That is usually the moment to skip the ballast entirely.
When not to replace the ballast
A new ballast puts you back on fluorescent lamps. In California and several other states, new fluorescent lamps can no longer be sold, so a California fixture that needs a ballast today will need lamps you can't buy tomorrow. See our guide to state fluorescent bans.
The alternative is a Type B (ballast bypass) LED tube. An electrician removes the ballast once and wires the sockets to line voltage. The tubes cost a little more than fluorescent, but there is no ballast left to fail. If you are replacing ballasts one at a time across a property, run the numbers on converting the fixtures instead.
Replace the ballast when the fixture runs specialty lamps with no good LED option, when lamps are still legal and in stock where you are, or when you have a storeroom of lamps to use up.
Find your replacement
- Linear fluorescent ballasts for T8, T5 and T12 tubes
- Compact fluorescent ballasts for pin-base CFLs
- Emergency ballasts for fixtures that must stay lit during an outage
Not sure what you're looking at? Text a photo of the ballast label to 949-589-3020 and a Lighting Specialist will match the ballast, or the LED tube that replaces it. Orders can be picked up at our Irvine location or shipped.
