Fluorescent starters or glow starters are used to help fluorescent tubes and lamps ignite in the initial starting stage of their operation.

Simply put, fluorescent starters are a timed switch. The switch opens and closes until the fluorescent tube ‘strikes’ and lights-up. If the fluorescent tube does not light, the switch repeats it’s open/close cycle and the fluorescent tubes attempts to ignite again.

Read on if you would like to know more about this process…

When power is first applied to a fluorescent fitting, the current creates two electrodes inside the fluorescent starter to heat and glow. This causes one of the electrodes in the fluorescent starter to bend towards and make contact with the other electrode. This closes the switch and the current now passes through the fluorescent starter and on to the rest of the fitting. This means that the circuit across the fluorescent tube and the ballast in the fitting will effectively be switched “in series” to the supply voltage.

The current that is now flowing into the fluorescent tube causes filaments at each end of the fluorescent tube to heat up and begin to emit electrons into the gas that exists inside the fluorescent tube by a process known as thermionic emission.

Inside the fluorescent starter, the touching electrodes short out the voltage sustaining them and they begin to cool down and bend away from each other. This then opens the switch within a second or two.

The current through the filaments in the fluorescent tube and the ballast is then interrupted, and with the circuit no longer in series, the full voltage is applied to the fluorescent tube filaments and this generates an inductive kick which provides the high voltage required to start the fluorescent tube.

If the filaments were not hot enough during the initial cycle, then the fluorescent tube does not light, and the cycle repeats with the starter heating up and closing the circuit again.

Several cycles are usually needed to ignite the fluorescent tube and this causes flickering and clicking during the starting stage.

Once the fluorescent tube strikes, the starter switch does not close again because the voltage across the lit fluorescent tube is insufficient to re-start the heating up process of the electrodes in the fluorescent starter.

The older the fluorescent tube is and the older the fluorescent starter is, the less efficient they are at igniting. A tube that takes more than a few seconds to start-up is a clear indicator that the tube and starter may need replacing.

Types of Fluorescent Starters

Fluorescent starters can be identified by a designated wattage written on the side. The wattage is directly related to the length of the fluorescent tube it is designed to work with.

Listed below are the 3 most common types of fluorescent starter:

Series Twin Tube
FS2 Series Starter
Up to 22W

For use with fittings with multiple fluorescent tubes.

Single Tube Starter
FSU Universal
4W to 65W

2ft 18W, 3ft 30W, 4ft 36W and 5ft 58W fluorescent tubes.

Single Tube Starter
70W to 125W

6ft fluorescent tubes of 70W and over.

2D Lamps and T9 Circular Lamps

As a general rule, lamps with 2-pins have the starter built into the body of the lamp but 4-pin versions need an external fluorescent starter.

When replacing a 2D or circular lamp make sure you replace like-for-like with the appropriate wattage.

How do you know if you need a new starter?

  • A flickering fluorescent tube.
  • The fluorescent tube does not light.
  • Fluorescent tube lights at one end only.
  • Fluorescent tube lights at the ends only but not in the middle.

When considering re-lamping an area with multiple tubes we suggest replacing all the old tubes for new.

Older tubes lose colour and can appear dull over time. New ones alongside will look brighter and cleaner.

Re-lamping all the tubes in the room together will give an overall uniform appearance.

Make sure you read our handy guide to replacing fluorescent tubes.

We also advise replacing all fluorescent starters whenever you replace a tube. This ensures a prompt and efficient start-up, promotes maximum performance from the tube and can extend tube life.

Please note that LED tubes are supplied with their own special starter – which is essentially a circuitry which bypasses the function that a normal fluorescent starter would perform (LED tubes do not need to “heat up”). NEVER use a fluorescent starter with an LED tube.

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August 18, 2020 9:34 am

This was very helpful in understanding how starters work thank you

September 5, 2020 3:46 pm

Very helpful. Now I know that the starter I have is correct for the tube, and when I should change it.

October 31, 2020 3:13 pm

I’m replacing T5 8W 12inch tubes, two per fitting. There are also two starters in the fitting. Does that mean that the FSU is the correct starter?

Mat @ Lightbulbs Direct
November 16, 2020 9:34 am
Reply to  Matt

Hi Mat, no, you will need our FS2 series starter

Derek Gavin
Derek Gavin
November 19, 2020 9:23 am

apologies if this is a daft question. One of my under kitchen worktop strip lights…narrow bulb version…( a few years old now) has stopped working. New strip light bulb I purchased also does not work.Tested the electric current to the fitting and its working so concluding the fitment itself is broken ..
My question …does my form of narrow strip light under kitchen unit have a starter in it anyplace which i could renew as I cannot see one. I have changed starter units in my larger garage strip lighting.

Mat @ Lightbulbs Direct
November 19, 2020 4:09 pm
Reply to  Derek Gavin

Is the strip light you are referring to a T5 fluorescent tube or a double ended tubular lamp? T5 fluorescent tubes have electronic control gear built into the fitting, whereas a double ended tubular runs at 240V and has no control gear.

Derek Gavin
Derek Gavin
November 19, 2020 4:31 pm

Its a T521S2W 21 W fitment.
So from your reply it looks like its a T5 with control built into the fitting?…so not repairable ?

Mat @ Lightbulbs Direct
November 23, 2020 9:40 am
Reply to  Derek Gavin

There will be an electronic control unit inside the T5 fitting and it could be possible to replace the unit out. We don’t stock replacements, but if you search Google for “21w t5 control gear” you will find other retailers that do sell them. If you open up your fitting and see if you can find the brand or model of the control gear inside, you may even be able to purchase the same model. Check prices though, as you may find it more cost effective to simply replace the fittings.

Derek Gavin
Derek Gavin
November 23, 2020 2:54 pm

thanks and extremely helpful. Think a new unit is called for.What I intended anyway but wanted to make sure it was not just a simple fix before doing that….help appreciated

Will Ko
Will Ko
December 21, 2020 12:07 am

Do starters use more power than the tubes?

Mat @ Lightbulbs Direct
December 21, 2020 11:01 am
Reply to  Will Ko

No, not necessarily the starter, BUT there will be some control gear in the fitting that does consume power. This could add 10 – 20% to the rated power of the tube. If you are using an LED tube, often this control gear (and therefore starter) can be bypassed by re-wiring the fitting (using a qualified electrician) – this would result in the power consumed to be the same as the rating of the tube with no extra power being consumed. The LED tube will include a re-wiring diagram in the instructions that come with the LED tube.

January 27, 2021 8:58 am

I purchased several Crompton LED tubes from you. I now need to replace one of the LED starters. I am unable to find them listed on your website (or any where else!). How do I get a replacement?
Thank you

Mat @ Lightbulbs Direct
January 27, 2021 4:48 pm
Reply to  Robert

Hi Robert, we do not supply the LED starters individually as they only come supplied with an LED tube. However, if you contact Crompton Lamps on 01274 657088 maybe they can assist?