Easy fixes for slow to start, flickering or faulty fluorescent tubes
If your tubes are experiencing any of the following problems this article will tell you how to fix them:
- The fluorescent tube won't turn on (and is or isn't buzzing)
- The tube takes a long time to warm up and come on
- The middle of the tube won't light but the ends are lit
- The tube constantly flickers on or off
We are going to tell you what has caused the problem and how to check your starters and ballasts.
Image: Copyright 2006 Publications International, Ltd.
The fluorescent tube won't turn on
- No electrical power due to a tripped breaker or blown fuse
- A dead or dying ballast
- A dead starter
- A dead bulb
Check the power supply to the bulb
Start by checking the fuse hasn't tripped the power supply. Usually when this happens, more than one light will have tripped so check a few light switches and if none of them turn on, check your fuse box.
Test the tube
- Turn off the power switch to the bulb
- Rotate the tube 90 degrees until it stops turning, then slide the tube downwards
- Check both ends of the tube for darkened glass. If the tube is dark at each end then it's either defective or near the end of its life, so will need changing anyway
- If the colour of the bulb looks OK then try it in a different fitting which you know is working to see if it lights.
- If it doesn't light then the bulb needs replacing. If it does light, then the issue is likely to be with the starter
Checking and fixing starters
- A starter is a small box in the light fitting which the tube sits next to.
- The function of that starter, as the name suggests, is to feed enough energy into the tube so it lights it up.
- Starters are only found in fittings that are 15 years old or older.
- They cost as little as 20p - the easiest way to test a starter is to buy a new one and replace the old one.
How to find and replace your starter:
- If you can't see the starter, then remove the tube as sometimes starters are fitted underneath the tube, but remember that only older fittings have starters - if the fitting is modern then you could be looking for something which isn't there.
- Turn off the light switch and remove the starter by gently pushing it in and twisting it to the left
- Simply replace the starter and see if the light works
Checking and fixing ballasts
Image: Ballast in a flourescent lamp.
- A ballast gives a bulb enough voltage to start it, but then limits the amount of current going to the bulb, enabling the bulb to give off a steady light.
- A giveaway that a ballast isn't working properly is a buzzing sound coming from the bulb.
- If you have more than one bulb in a fitting and all the bulbs are flickering or out then it's highly likely to be the ballast.
How to check the ballast:
- Turn off the light at the switch and turn off the power supply to the light via the circuit breaker.
- Remove the tube from the fixture, as the ballast is usually found behind the bulb or between the bulbs in a fitting with more than one tube.
- The ballast will usually have a cover on it so remove the ballast cover using a screwdriver and check the ballast, which is usually a rectangular shaped grey or black box, to see if it's leaking oil or if it looks burnt.
- Firstly, check all the wires are connected properly as loose wires could cause the ballast not to work properly, if the wires are properly connected, then the problem is likely to be with the ballast itself.
- Ballasts come in all shapes and size so if you do need to buy a new one, check the measurements carefully when buying online, or take the old ballast into the lighting shop with you.
- Your ballast is likely to have a wiring diagram on it (or if not there should be one in the box) which will show you which wires go where when replacing a ballast. Usually, the wires will be coloured red, white, blue, yellow and black and the corresponding colours on the ballast wires will match up with those in the fitting.
- There's plenty of videos on YouTube which demonstrate how to change a ballast safely, this is one of our favourites for changing a T8 ballast.
Please note that there are many different types of ballast and each one will have different instructions for changing. There is risk of electrocution when changing a ballast so please ensure you know what you're doing or ask an electrician to do the job for you if you are unsure.
Other problems that can be identified and fixed with the above checks
The middle of the tube won't light but the ends are lit
- Check the starter
The tube constantly flickers on or off
- Check the starter
- Check the ballast
- Check the lamp you've used in the fitting is the correct size and fitting
The tube takes a long time to warm up and come on
- Check the starter
If you have any questions about fluorescent tubes then we'd love to know! Contact us on firstname.lastname@example.org and we'll add the question and answer to this page!
To buy lighting related products online, follow the links below:
- Starter switches
- Emergency combo ballasts – Normal high frequency ballasts and an emergency backup feature in one for fluorescent lamps to be used with an emergency battery.
- Electronic HID ballasts – To run high intensity discharge lamps with a flicker free start (HID) e.g. Metal Halide lamps.
- HF ballasts – High frequency ballast to run a fluorescent lamp (turn on turn off without flickering).