Turn off the power before you touch anything

The first step is always to cut power to the light. Flip the wall switch to off, then go to your circuit breaker or fuse box and switch off the breaker that controls that light. If you are not sure which breaker it is, turn off the main breaker — it is safer to work in the dark for a moment than to touch a live fixture.

Wait a few minutes after cutting power. Fluorescent tubes and ballasts (the electrical box that makes them work) stay hot for a short time even after the power is off. Touch the fixture lightly with the back of your hand first — if it is still warm, wait another minute or two.

Key Takeaways

  • Always turn off the breaker before touching any part of a fluorescent fixture, and wait for it to cool.
  • Fluorescent tubes twist or slide out depending on the type — T8 and T12 tubes twist a quarter turn, while some older fixtures use slide-out pins.
  • Ballasts (the electrical box inside the fixture) last 10 to 20 years and must be replaced if the fixture hums, flickers, or refuses to turn on even with new tubes.
  • Ballast replacement requires disconnecting wires and bolts, so if you are not comfortable with electrical work, hire a licensed electrician.
  • Disposal of old fluorescent tubes must follow local rules because they contain small amounts of mercury — many hardware stores and waste facilities accept them for free.

Replacing a fluorescent tube

Most residential fluorescent tubes are either T8 (one inch in diameter) or T12 (1.5 inches in diameter). The easiest way to tell which you have is to look at the number printed on the tube itself, or measure the diameter with your fingers. T8 tubes are narrower and more common in newer homes.

To remove a T8 or T12 tube, grip it gently with both hands near the middle and twist it a quarter turn counterclockwise — about 90 degrees. The tube will slide out of the socket pins. If it does not move after a quarter turn, stop and check that you are twisting in the right direction. Do not force it.

Slide the new tube in by aligning the two pins at each end with the two slots in the socket, then twist it clockwise a quarter turn until it stops. The tube should sit flush in the fixture. If the new tube does not light after you turn the breaker back on, the ballast may be failing — see the section below.

When the ballast needs replacement

The ballast is the rectangular electrical box mounted inside the fixture. It regulates power to the tubes. If you have replaced the tubes and the light still does not work, or if the fixture hums loudly, flickers constantly, or smells like burning plastic, the ballast has likely failed.

Ballast replacement is more involved than tube replacement because it requires disconnecting wires and bolts. Turn off the breaker again and locate the ballast — it is usually a gray or black box about 6 inches long bolted to the inside of the fixture. Take a photo of the wire connections before you disconnect anything, so you know where each wire goes.

Unbolt the old ballast using a wrench or socket set, then disconnect the wires by loosening the terminal screws or unclipping the connectors. Buy a replacement ballast rated for the same wattage and tube type as your fixture — the old ballast will have this information printed on it. Connect the new ballast by reversing the steps: bolt it in place, reconnect the wires to the same terminals, and test the light.

If you are not comfortable working with electrical connections, hire a licensed electrician. A ballast replacement usually costs between $100 and $200 in labor, and the ballast itself costs $20 to $60 depending on the type.

Replacing an entire fluorescent fixture

If the fixture itself is cracked, corroded, or very old, replacing the whole unit may be cheaper than fixing the ballast. Turn off the breaker and take a photo of how the wires connect to the fixture. Most fixtures are bolted to the ceiling or wall — unbolt them and disconnect the wires by loosening the terminal screws.

Buy a replacement fixture of the same size and wattage. New fixtures come with instructions that show exactly where each wire connects. Connect the wires to the terminals on the new fixture, bolt it to the ceiling or wall, and test it. If the new fixture does not light, check that the breaker is on and that the tubes are twisted all the way in.

Fixture replacement is a good time to consider switching to LED tubes or LED fixtures instead. LED tubes fit into existing fluorescent sockets and use about 75 percent less power, though they cost more upfront. LED fixtures are even more efficient and last 25 to 50 years, so they may save money over time if you use the light frequently.

Disposing of old fluorescent tubes safely

Fluorescent tubes contain a small amount of mercury, which is toxic if the tube breaks and the powder inside is inhaled. Do not throw them in the trash. Most hardware stores, waste management facilities, and recycling centers accept fluorescent tubes for free or a small fee. Call ahead to confirm they take them, and ask whether you need to bring them in a box or bag.

If a tube breaks while you are handling it, open windows to ventilate the room and sweep up the powder carefully. Wear gloves and a dust mask if you have one. Put the broken pieces and powder in a sealed plastic bag and take it to a hazardous waste facility. Do not vacuum the powder — vacuuming spreads it into the air.

Common mistakes that waste time and money

The most common mistake is twisting the tube the wrong direction. Fluorescent tubes always twist counterclockwise to remove and clockwise to install — the opposite of a light bulb. If the tube does not come out after a quarter turn, you are probably twisting the wrong way.

Another mistake is buying the wrong ballast type. Ballasts are rated for specific wattages and tube types — a ballast for a 40-watt T12 will not work in a fixture designed for a 32-watt T8. Check the old ballast label before you buy a replacement, or bring the old ballast to the store to match it.

A third mistake is assuming the fixture is broken when only the ballast has failed. If the tubes light but the fixture hums or flickers, replacing the tubes first costs almost nothing and often solves the problem. Only replace the ballast if new tubes do not fix it.

Frequently Asked Questions

Can I use an LED tube in a fluorescent fixture?

Yes, if your fixture has an electronic ballast. LED tubes designed for fluorescent sockets (called "ballast-compatible" tubes) work in most modern fixtures. However, some older fixtures with magnetic ballasts are not compatible. Check the tube packaging or ask at the hardware store whether it works with your ballast type.

Why does my new fluorescent tube flicker?

A new tube that flickers usually means the ballast is failing or the tube is not twisted all the way in. Remove the tube, clean the socket pins with a dry cloth, and reinstall it firmly. If it still flickers, the ballast needs replacement.

Is it safe to replace a ballast myself?

Ballast replacement involves electrical connections, so it carries a risk of shock if the power is not fully off. If you are not experienced with electrical work, hire a licensed electrician. The cost is usually $100 to $200 in labor, which is worth the safety.

How long do fluorescent tubes last?

Standard fluorescent tubes last 7,000 to 15,000 hours of use, which is roughly 5 to 10 years in a typical home. High-efficiency tubes last longer but cost more. LED tubes last 25,000 to 50,000 hours and use much less power.

What should I do if a fluorescent tube breaks?

Open windows when ready to ventilate the room. Wear gloves and a dust mask, then carefully sweep up the broken pieces and powder into a sealed plastic bag. Take the bag to a hazardous waste facility. Do not vacuum, as it spreads mercury powder into the air.