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 FS125 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 circuit 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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Joyce Williams

Can I replace an old FS-5x 4,6,8 WATT starter with a FS-5 4,6,8 WATT?

Lee Clements

what will happen if i use a a st151 22w starter instead of a 155/800 starter


I have a bad FS-2C, How would I determine if need the 2C or if I could replace it with an FS-2 ?

Mat @ Lightbulbs Direct

The C stands for Condenser – this type of starter has an extra capacitor in it’s circuitry to make a smoother electrical output. You should be able to swap out with a FS-2 with no issues.


I have recently replaced a starter. Can I recycle the old one? I was wondering if I could take it to somewhere that takes old electricals for recycling (eg Currys).

Mat @ Lightbulbs Direct

Hi Therese, although we offer our own WEEE (Waste Electrical) recycling facility, for something as small as a starter you may want to look up somehwere local to you. You can find Local Authority owned facilities or you may find your local B&Q offers a free WEEE disposal facility.


Replacing a T9 4 prong bulb. The ends dimly lit orange and nothing in the middle. Is this a bad ballast? Bad bulb? Does the entire light fixture need to be replaced?

Mat @ Lightbulbs Direct

Could be both, bad tube or bad ballast. If you bought the tube from us, you could try purchasing a new tube, and if it works fine, then let us know and we will refund the full order for the first tube.


If I have an older fluorescent light fixture that uses a starter, then I can’t switch the tubes to LED tubes? I would have to replace the entire fixture or stick with the older type tubes?

Mat @ Lightbulbs Direct

Hi Reb, our LED T8 tubes come with a special LED starter that you swap out when you install the tube meaning they are a simple replacement for flourescent tubes.


What do I do if my LED is starting to have a slight delay in turning on. Does that mean new bulbs? The bulbs are 3ft tubes.

Mat @ Lightbulbs Direct

Hi Jody, with this being a tube, we suspect that the ballast in your fitting may be the cause. You could try a new tube and see if the same thing happens?

Philly de Lacey

I can’t find the start on a duo lamp system – can you let me know where to find it?

Mat @ Lightbulbs Direct

Hi Philly, chances are that your fitting uses a high-frequency electronic ballast that supplies it’s own boost to light up the lamps. There is no requirement for a starter in these type of fittings.

Jane smith

Helpful thanks

Brenda Hoffman

What is the difference between an fs-5 starter and an sfv-5 starter? Are they interchangeable?

Mat @ Lightbulbs Direct

Sorry Brenda, I can’t find any information on this starter. Perhaps you could type out all the text you see on the starter and we may be able to identify it.


I have a Blackflag bug zapper 5500 40w for about 5 yrs, it has worked perfectly up until recently.
It’s got the 4pin receptacle and on the backside of it with the wires it has a 1250V HEL 472J capacitor soldered to this receptacle . It’s also got the black U Shaped Florescent Tube.
I’ve been reading a lot and I did see on a few sites that some equipment has a start capacitor instead of the micro starter, maybe newer technology? I say this because I cannot find a micro starter anywhere.
On the board there are some thumbnail sized encased in the metal housing like the larger starters I’ve seen the pictures of, but the ones on my board are much much smaller and smaller diameters also. Again thumb nail size and much smaller.
Thank you in advance
Great thread going here

Mat @ Lightbulbs Direct

As all UV lamps are fluorescent technology, they all require the same standard of technology to ignite the tube. As long as the unit is in working capacity, you should just replace the tube like-for-like, i.e. a 40W U shaped 4-pin tube.

Ty Risk

My housing commission flat does not have a see-able starter fuse for my fluorescent light tube

Mat @ Lightbulbs Direct

You may have an electronic ballast in the fitting which doesn’t require a starter, but would not the housing commission be responsible for replacement of tubes?


Hello, Can you tell me the difference between an FS-4C 13-30-40W starter and an FS-4 13-30-40W (No “C” in the second one) and can I buy them from you? Also may I use a 40W starter with a 25W tube? Thanks, Nancy

Mat @ Lightbulbs Direct

So the ‘C’ stands for the old-term ‘condenser’, a more modern way of explaining this is that there is a capacitor in the starter. This capacitor makes the electric current in phase with the ballast in the fitting ensuring a smoother and slightly more efficient electrical supply to the tube. We do not sell FS-4 starters of either type, but a quick google search shows various websites that do. I would suggest you contact one of them to ask about wattage and whether you need to use a C or non-C.


Thank you so much.


I have 4pin energy lamp for bathroom what size starter do I need

Julia Dykes

Hi, I need to replace the starter on a bulb on an industrial embroidery machine. The starter on there at the moment is an NEC FG-4P 36.40. I’ve tried to find a replacement, but I’m guessing it’s a Japanese starter. Is there a UK equivalent? I’d be grateful for any help – I don’t want to blow aa fuse! Thanks.

Mat @ Lightbulbs Direct

Tough one, on the face of it, this looks like a simple 40W starter, but we cannot find any technical data-sheets to back that up, and we certainly wouldn’t want to recommend a wrong solution. We did, however, notice that there are various sellers on Amazon who can ship this starter from Japan to the UK, some in boxes of 25, so might be worth getting a bulk shipment in like that to keep you going for a few years?

Last edited 4 months ago by Mat @ Lightbulbs Direct
James Gilpin

I have a bathroom mirror with integral 18W F18/T8 600mm fluorescent tubes. I can’t see a starter anywhere. Can I replace these tubes with LED equivalents?

Mat @ Lightbulbs Direct

You can, but you would have to re-wire the fitting to bypass the fluorescent transformer inside the fitting. Then an LED tube like our 2ft Cool white T8 tube would be an excellent equivalent.

Doreen Broomfield

The starter needs replacing on my fluorescent tube and I am having problems trying to replace the starter. Whilst it is supposed to be a standard fit, I have purchased 2 of the correct wattage and whilst it looks the same, does not fit snuggly the way the old one does. The one I have is 4-65W made by Kingfisher. Can you help?

Mat @ Lightbulbs Direct

Starters have a universal fitting meaning that any brand of starter should fit. I suspect something is wrong with your fitting, maybe something has become corroded or bent out of shape?

Lee Newton

The starter should rotate roughly a quarter-turn anticlockwise for removal, and the opposite direction for insertion of a replacement. Perhaps the starter socket has become distorted. If the new device is not making contact you can tease out the starter socket contacts with a screwdriver to bring them back in play (with the luminaire isolated or course, though.


Just replaced the 4’ fluorescent tubes in my father’s garage. Looks like new starters are also required. Any idea what starter should be used to replace PGSU 200/250V single 32-40W starters?

Mat @ Lightbulbs Direct
Robert Deming Hoskins

I have a Budweiser pool table light it has two fluorescent tubes 33″ long. I put two new F2T12CW33 tubes and two new FS25 starters. When I turned the light on, I got a quick burst of light at one end of the fluorescent tubes and then nothing. I can’t find information on what tubes or starters it should have in this light.

Mat @ Lightbulbs Direct

Hi Robert, Although we don’t sell them, going by the part numbers, you’re starters aren’t rated with a high enough wattage. The tubes are rated at 33W, but the starter’s are rated at 25W – so they probably aren’t providing enough power to start the tube. You could try swapping out to our 4W to 65W starters.

sabra howell

can a bad tube and aged starter completely blow the power out in a bathroom??
how do i test a starter to see whether or not it’s still good?

Mat @ Lightbulbs Direct

Possibly – there is quite a large surge of power going to the tube to ‘fire’ it up and this could have tripped your circuit. Starters are pretty cheap to buy and we always recommend swapping out the starter to a new one each time the tube is replaced.

Tony Betts

A new replacement Sylvania FS11 70 w starter causes tube to flicker. Is there a more powerful starter available or is it time to replace the tube?

Mat @ Lightbulbs Direct

Is the starter kicking in again after the tube has been lit? If working perfectly, when the tube is lit, the starter remains open. So I suspect the tube is failing, or possibly the ballast in the fitting.


I’m replacing a T12 75W, 110v Dual bulb starter. What starter do I need?

Mat @ Lightbulbs Direct

Having searched around the internet we cannot find any suitable starter – are you sure you require a 75W 110V?


Need to replace an electronic starter for a 40W circular tube. Old part is YZ140EA but only same size replacement I can find is YZ138EAA (ie. rated for a 38W tube). Any idea if I’m likely to hit a problem fitting the 38W starter?

Mat @ Lightbulbs Direct

A 38W starter may not provide enough ooompf to ignite a 40W tube, but why couldn’t you use a FSU starter which are rated from 4W to 65W? Is it a high frequency fitting?


Hi – if I remove the tube but not the starter, does this still use electricity or none at all?


I have an old 12″ light in our bathroom with a bad starter. The starter is an FSV-12 for 32 w circline. Obviously it is not the correct one but it worked for decades. However, it is unique from any I’ve ever seen because it has a groove in the head of the pins. A regular FS2 will not fit in the socket. I don’t see any on-line. Is this an obsolete starter? Is there a small ballast replacement for this like there is for the 4 ‘ ceiling lights?


Mat @ Lightbulbs Direct

Sorry to hear you are having difficulty in finding these starters – they are not familiar to us either. Does the FSV-12 starters have a brand name for a company you could contact and see if they have any UK distributors?

Lee Newton

A 32W circline tube needs a FSU starter. That will run it absolutely fine. FSV12 was an old starter denomination that was declared unnecessary as anything from a 3ft 30W (which a 32w circline is, in principle) up to a 5 ft 80W will comply electrically. Fit a new lamp and an FSU, if you haven’t discovered this already 🙂

Derek Bird

I have a 4 pin T5 40w 6400k circular flourescent ring but i can’t find what starter i need, the one that is in has disintergrated so i don’tk now no. can anyone help please.

Mat @ Lightbulbs Direct

Starters are rated for the wattage of lamp they can be used with, so with a 40W tube, you could try our 4W to 65W starter


Do I need a starter for a new 28W CFL CC GR10q – 4pin, col. 835 – 3500K White? It’s taking about 5 mins to come on which isn’t great for a bathroom light. The lighting shop didn’t mention replacing a starter. I don’t even know what one if any to get. Thanks

Mat @ Lightbulbs Direct

No, they don’t use starters – BUT, the light fitting will have control gear inside to drive the lamp – this is probably on it’s way out. Probably time to replace the fitting, I’m afraid.

Lee Newton

Some fittings for 28w 4-pin 2D lamps do use starters. You will need a FSU if that’s the case in your luminaire. Don’t throw out the fitting unless you’ve checked this. Two-pin versions are the only type that absolutely do not require a separate starter as one is incorporated in the lamp itself.

Nick Goodall

You say “current creates two electrodes inside the fluorescent starter to heat and glow”. Would it be better to say “current causes two electrodes inside the fluorescent starter to heat and glow”?

Larry Rueff

This article actually does NOT explain how starters work. The starters are actually gas tubes. The gas lights up and the current causes it to heat up enough for the bi-metal strip to bend and make contact between the electrodes. When that happens the current is directed through the filaments of the fluorescent lamp in series. THEN, they cool off because the contacts are connected. When they cool off and disconnect the ballast current spikes a voltage across the lamp which now has hot filaments and the tube lights. The voltage across the now lighted lamp is too low to relight the starter.


Have question .. why with new bulb & starter does flourescent still flicker. I have to remove starter to get bulb on & is fine.

Lee Newton

Wrong starter. Specifics would help. In another comment, I have left a table of starters and suitable lamps. What is happening is the operating voltage of the tube is above the critical enagaging voltage of the starter causing it to operate, if the tube runs fine when it is removed.


Hi. The starter on my old stove’s fluorescent light blew and shattered. I’m using t8, 18 watt double ended fluorescent tube. Hard to still find, but I stocked up. If it makes any difference, the ballast is magnetic. So would the universal FSU 4 watt to 65 watt single tube starter work for me? And is it normal for the old starter to shatter and flash when it needs replacement?

Mat @ Lightbulbs Direct

Hi Nancy, firstly, yes, the FSU 4W-65W starter is correct for you. I’ve certainly not come across an old starter shattering before – I can only assume the material has degraded over time due to the heat of the stove.

Brian Hanley

What is the difference between a FS-2 and FS-5 Starter. They both seem to work fine in an 18″ bar light? Are they interchangable?

Les Cooper

Some starter state ‘with condenser’ and others don’t. My existing starter is an FS-U 65-70w with condenser for a 6 foot tube. What is the difference if any?

Mat @ Lightbulbs Direct

Hi Les, it’s just terminology, condenser vs capacitor – they are all the same thing. You are able to replace with Crompton Lamps Fluorescent Starter FSU 4W – 65W or Crompton Lamps Fluorescent Starter 70W – 125W (depending on the wattage of your tubes).

denis kirby

i have got 58w t26 light what starter would i need

Mat @ Lightbulbs Direct

Can you use a FS-2 starter 14.15.20w to replace a FS-U 14.15.20w starter ? Thanks

Mat @ Lightbulbs Direct


Olufemi Odusola

Hi there, before I read this message, I didn’t know what it was all about, but the Fluorescent in my kitchen failed to switch on, then all what you said made sense to me, I’ve now changed the Starter which wasn’t working properly & I saw that the Fluorescent started to work properly.

Thanks for your help.

David Becker

What was the last year that they made fluorescent fixtures with starters??

Mark S

Useful article, thanks.  I’ve noticed that FS125 starters have been installed on a number of fittings that have 36w, 58w and 70w tubes.  I guess at some point someone thought its easier just to buy one box to cover all fittings.  Is this an issue for the lower wattage tubes or should FSU be swapped in?

Mat @ Lightbulbs Direct

FS125’s have a rating of 70W – 125W, so yes, we would advise swapping to FSU starters on those 36W and 58W fittings.

Lee Newton

They’ll operate, but suboptimally. Risk of cold-starting that might wear out the lamp prematurely. FSU for the 36w and 58w, and FS125 for the 70w should be fine.


I tried to insert starter unit it went straight through into the strip light what can l do

Mat @ Lightbulbs Direct

For safety reasons it would be best to replace the fitting. Something may have broken inside the fitting.


The starter unit went strait through the hole what can l do


Thank you for all the good info on your website! I was wondering if an FS-2 starter can substitute for an FS-2C. I cannot find the 2c starters and any references on the web seem to be from people who bought FS-2 starters and say that it is ok based on that it seems to work
This is for a lamp that is 22 years old. It is in a kitchen pantry and is usually only on for short periods of time so I really don’t need to buy an LED to save electricity. There is a Phillips F20T12/0 bulb in the lamp.
So is an FS-2 ok or should I replace the whole lamp. I don’t want there to be any problems. Thanks!

Mat @ Lightbulbs Direct

Just done a search for FS2C and can’t find anything decisive on that code. Certainly the wattage of a FS-2 is in tolerance with the F20T12/0 tube you have fitted – so it should work.


Useful, but it would be helpful if there were some diagrams showing what is connected to where, especially: the 4 pins on many tubes; where, electrically, the starter is connected, etc.


The starter of my tubelight seems to be stuck onto the holder. I twisted it anticlockwise by pressing down but just wouldnt come out. Is that how it is done?

Mat @ Lightbulbs Direct

Yes, push down and a quarter turn anti-clockwise. Sorry to say, but it sounds like the starter or fitting could be faulty.


hello there and thanks for this great post, quick question.. my starters (both of them) flicker in red when turning on the light but when the lights are on they will stay glowing red (not flickering and not off) is it ok for starter to stay glowing red/on like that while the lights are on ? and they turn off when the lights are off .. it only happens in one room .. in other rooms the starter turns off after the lights turn on and ofcourse when the light are tuned off so they only flicker when the light is turning on and then they turn off when the light is on .. new starters btw

Mat @ Lightbulbs Direct

That doesn’t sound right – have you tried replacing the starter?

Kaegen Lau

I’m sorry but this is all way over my head (anything at all to do with electricity or circuits etc.).
My T8 tubes are having trouble lighting up quickly and the center of these brand new bulbs are dim, while the ends are bright. I have two separate ballasts (single fluorescent T8 bulb) for my aquarium, which use 25w 36″ tubes. They work, but it takes several seconds for them to light.
The ballasts came from the manufacturer with FS-4 condensers, but they didn’t work well. I’ve since used FS-2 and FS-4 starters, and I can’t tell which one I need, or what the differences are between them (there are no clear answers anywhere on the internet). Which one do I need, or is there some other completely different starter I need?
If someone could please explain starter differences to me in the simplest of terms, I would be most grateful.
Thank you.

Mat @ Lightbulbs Direct

I think the FS-4 starter is quite specialist, and if this is what was installed in your fitting prior; then you should replace with the same type. They are readily available if you do a quick google search

Kaegen Lau

Thank you for letting me know! Since my posting the question, the new FS-4 starters I had installed are now making a loud buzzing sound, and this has me really concerned; the bulbs are also still dim in the center and bright on the ends. The starters and the bulbs are both brand new, and the ballasts are only a couple years old; I’m not sure what’s going on here. : (


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

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?

Will Ko

Do starters use more power than the tubes?

Mat @ Lightbulbs Direct

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.

Derek Gavin

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

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

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

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

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


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

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


Thanks for the helpful reply. What I don’t understand is, if the tubes are being used in series why are the tubes rated at 240V and not 110-130V? (I’m referring to sku 1464). Thanks.

Lee Newton

It is meaningless for manufacturers to quote mains voltage for a fluorescent lamp, as it is the gear that drives them with a nominal voltage drop (in the case of your 12″ tube that’s 56V). However starters themselves do require the mains voltage for operation (single short lamps run from 110v supplies might not ignite reliably with an FSU starter, for example)

David Quarendon

Why is the FSU not suitable? They are rated 4W upwards, and the bulbs are 8w. Would make it easier to use spare ones on other larger fittings.

Mat @ Lightbulbs Direct

The original question was in relation to two tubes in series, therefore the series starter is required. If your fitting uses a singular 8W tube the the FSU is fine.


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