The 2D Compact and 2 Pin 4 Pin technical information

The 2D Compact Uses and Applications

The standard fluorescent tube and the compact version the CFL has now matured into a very usable lighting product. Going back to the 90’s they were around and did save energy but did have their technical problems. One of the main issues with the fluorescent tube was the flicker and the dependency on good electronic integration with the starter. There were certainly many tubes that used to just flicker the whole time, become a nuisance and just end up being turned off. These days the technology has advanced considerably and often have integral starters especially in the CFL types which make far easier electrical installations as no external starter of high frequency control gear is needed.

2D compact

The 2D compact version of the CFL ( compact fluorescent lamp) is also extremely popular these days.  The main uses of the 2D compact are within commercial applications where is is necessary to have a bright but compact lamp that will fit into a light fitting which can either be ceiling or wall mounted. As a consequence there are a whole range of different 2D compact lamp fittings available on the market which are used extensively in car parks, warehouses, corridors in flats, hotel areas not exposed to customers, retail outlets, office buildings  and the list goes on.  As these lamps are energy efficient saving around 80% in electricity compared to standard incandescent light bulbs then they have really taken over as the standard for this classification of installations. Quite often these lamps are connected to PIR units so they just light on demand when somebody passes the senses which makes them ideal for corridors areas which are not continually used and it would not be economical to leave the lights on the whole time!

Type of 2D Compacts and 2Pin / 4 Pin explained

The 2D compacts come in 3 main sizes, the 16w, 28w and 38w lamps. The 16w is a small units around 135mm square  and the 28w and 38w are larger measuring about 200mm square. This means than the light output is very good for the size of lamp with the 38W typically producing 2900 lumens which means where space is a premium and there is no room for fluorescent tubes the 2D compact is an ideal solution.

The lamps come with 2 types of cap fitting either the 2 pin 2D compact or the 4 pin 2D compact. The 2 pin has its own built in starter and the 4 pin lamp is configured to use with external electronic control gear either of the standard or high frequency type.

2D compact GR8: This is a 2 pin fitting generally used on 2D LEDs and CFLs

2D compact GR10q: This is a 4 pin fitting generally used on 2D LEDs and CFLs

Main Drawbacks of the Fluorescent 2D Compact and the advantages of the LED 2D Compact


The 2D compact has 3 main drawbacks. Firstly if it is used with PIR units the constant switching on and of will shorten the lifespan of the lamps,  secondly if they are left on for long periods they do use a significant amount of electricity and thirdly the lifespan is only typically 10000 hours. This is where the 2D LED comes into play, The 2D LED is far more efficient and only uses around 50% of the  electricity of the CFL 2D compact and the additionally the LED technology is far more suited to rapid switching and you will not see a reduction in life. Finally the typical life is around 35000 hours which is 4 years of continuous use as opposed to just over 1 year for the fluorescent 2D compact. However, the 2D LED is considerably higher investment so it is worth doing a cost analysis.

45 thoughts on “The 2D Compact and 2 Pin 4 Pin technical information”

  1. Ive changed the bulb and still no light, main fuse/trip switch is ok and there is power getting to it. Is there a starter or fuse in the actual unit that i need to check. if so where is it? Its a 2D 4pin Pl Bulb

    1. Hi Derek

      A 2D LED or 2D PL lamp has the driver built into the actual bulb. This means that if you are fitting into an existing fitting you need to bi-pass the ballast.

    2. My electrician fitted 4 pin cfl lights with no visible starter ,when I had to fit a new lamp it would not work. It would appear that the units have an internal starter.What do you think is wrong.?

      1. The CFL 4 pin has a ballast which need to be in the fitting. Maybe this was not fitted!
        If there is no ballast then you could use an LED lamp which does not need any ballast at all as you simply wire it straight across the mains.

  2. I have fitted the correct 4 pin 2D bulb but having no joy. The ends of the bulb nearest the fitting are glowing slightly but not coming on. What do I need to do? I’m a complete beginner when it comes to electrics so no industry speak please. Thanks

    1. Hi Dane

      these PL lamps just need pushing in so they are easy to fit. This sounds like it could be one of 2 problems as the correct power is not getting to all the 4 wires to the tube. Either the ballast, lamp holder or bulb is faulty. Best thing is to try a bulb you know works in this light and then you will know if it is the bulb or the ballast and then replace the failed part.

        1. You could look on the side of the ballast and google the details or alternatively it might be easier just to buy a new light fitting!

    1. It can either be the bulb itself but it is more likely to be the control gear in the fitting. A 4 pin has a ballast which has to ignite the fluorescent gas and a 2 pin a choke. The best thing is to try swapping the bulb and if this does not work then you will need to change the control gear in the fitting or if this is not possible the whole fitting.
      Paul SLB

  3. The 2D 4 pin 21w CFL has gone in my 21w bathroom light fitting. The 21w bulbs seem to be going obsolete, but 16w are readily available. The socket and dimensions seem to be identical. Can I fit a 16w to a 21w rated fitting? (albeit a slight reduction in light output)

    1. The 16 watt and 28 watt 4 pins certainly have the same type of control gear so both can work off the same. Clearly you have to check that the control gear will take the power consumption of the light ie. 16 or 28 watts. I have not heard of the 21 watt versions but on this basis then the 16 watt should work.

      1. Thanks for that. I understand the 16w and 21w CFLs were the same plug size and external dimensions, but the 28w CFL is physically larger, so probably would not fit inside the globe. In any case, as you say, the existing 21w ballast in the fitting would not support a 28w CFL for long, so I’ll try a 16w CFL, which are presently as cheap as chips anyway!

  4. Why have 2 pin and 4 pin versions of the same thing (28W) or rather what’s the advantage of the ballast “ignition” over the choke? One DIY place told me the 4 pin version was an upgrade and safer (and hence they were no longer selling the 2 pin tubes). Is this true, please?

    1. The 4 pin is a more modern system and does work more effectively for 2D fluorescent bulbs. The 4 pin versions with the ballast do light up more quickly and a are less prome to flicker than the 2 pih. However in comparison to the 2D LED both are very poor.

  5. Can I put a 2-pin GR8 bulb in a 4-pin GR10 socket and have it operate safely?

    The socket previously held a 4-pin CFL that has now died. The replacement is a 2-pin LED unit.

    As I understand it the two extra pins on the 4-pin unit are to connect it to the external ballast. In contrast, the the 2-pin unit has it’s own ballast and does not need to connect to the external ballast. From that I assume it is missing the pins that the 4-pin bulb uses for that purpose.

    If this is so then it seems that I could put a 2-pin LED unit in the 4-pin socket, effectively ignoring the external ballast, and have it work correctly. Or am I missing something and about to burn the house down?


    1. Hi Lincoln

      In theory you could put the 2 pin LED in to the 4 pin soacket although you will encouter a practical issue because the 2 pins on the 2 pin socket are offset from the ones on the 4 pin socket so I believe you will find that it will simply not fit. One way to get around this is to fit a new 2 pin lamp holder. If you are able to connect the 2pin LED in then there still will be some requiring to do inside the light fitting because the 2 pin has a choke fitted. The choke is not needed for the LED so this will need to be rewired.



  6. I have tried replacing a previous bulb with new in my bathroom light, and it doesn’t work – the new bulb is 4-pin and I’m fairly sure the old one was 4-pin too (although it’s been thrown away so can’t be certain!). Is there any reason why a 4-pin wouldn’t work in a bathroom light? I have checked for loose wiring and can’t find anything obvious.


    1. Found the solution… checked the same bulb in our neighbours house and found it was a 2-pin bulb – that worked, 4-pin bulbs didn’t.

  7. hi, i am in need of some advice. i have just replaced the 16w 835 2pin with this Wickes bulb.

    i have taken the old one out which seemed to be well fixed but now i have put the new one in im not entirely sure if its as well fitted. what i mean by this is that im not sure if it should click into place or if there should be any gaps when pushing it in. do i need to be more forceful as i have not heard any clicks and its at least 6mm away from top of the fixing. the light does work but have i done anything wrong?

    1. Yes the 2Ds fluorescent fittings and lamps sometimes do not seem to engage well. As long as it works and does not fall out you should be ok.

  8. I have a 16w 4pin DD electronic ballast EEI=A3 which has blown, the unit is a Landlite product but this ballast no longer appears on their website. The ballast is 73mm centre 22mm high 42mm wide and is fitted inside a slim line ceiling light. Can anyone help in finding this type of ballast or will a 18w 4pin DD ballast be ok to put in the light fitting along with the 16w 4pin DD bulb.
    Thanks guys

    1. HI there

      these should work with any 4 pin ballast that has the rated output.
      Best to try one first if you need a lot!



  9. Hiya,

    Just had one of these die, the first of my experience. It’s a 4 Pin tube. I bought a replacement Philips 4pin but it didn’t work. The packaging suggests it was a ‘high frequency’ bulb not intended to run on the mains? But looking in stores I’ve been unable to find a 4 pin 50 Hz light.

    Is it safe to use a 2 pin in the same fitting? Or should I find a Mains capable 4 pin? Or am I barking up the wrong tree entirely??


    1. These bulbs are everywhere and websites like AMAZON list literally dozens of brands BE aware that you cannot use a FOUR PIN in a TWO PIN fittment or vice versa neither can you use a different power [WATTAGE]rating The 4 pin is a more modern upgrade apparently and uses an external ‘starter’.
      Just enter the ‘spec’ number that appears ion the centre section on the reverse of where the pins are situated into your search engine I ordered mine at 1610 and it was delivered the next day . My own feeling is that the majority of these bulbs are pretty much re-badged generic items.

  10. I have just fitted new 2d 28 watt 4p in bathroom initially it worked but after a day i sometimes have to switch it on and off a couple of times to get it to work any ideas thanks
    S Vose

    1. These CFL tubes can take a couple of times to ignite and come on. If you change the ballast this should help. The other route is 2D LEDs and then you will have no problem as they come on instantaneously.

  11. Which of the four pins is which? When connecting the replacement ballast how do you know which wire to connect to terminals? No markings other than B1 and B2 on the original ballast circuit board.

  12. Hi I bought a 4 pin bulb Philips plq would this work on a 2d gr10q 4 pin is it the wrong bulb or should this one work

    1. The lamp should work and give more light but the issue is that you run the risk of burning out the control gear. Best to have a look at this first to see if it will handle 38 watts


  13. I have a floodlight with no sensor using a double D bulb 4 pin
    I have tried new bulbs but they don’t work. I have a live coming out of all 4 pins in the light unit. Why will the bulbs not work?

  14. I have recently replaced 4pin 2d lamp holder with 2pin 2d lamp holder. Somehow my 2d 2pin lamp is not working with this new lamp holder. Do I need to need to make any further changes in wiring for my bulb to work with this 2d 2pin holder.
    I have changed the bulb holder in old bulkhead which was working with 2d 4pin holder and 2d 4pin bulb.


  15. I have a 2D 4 pin CFL fitting with magnetic ballast and external starter. The plastic enclosing the has crumbled and connection to the ballast has broken. I have removed the ballast, but cannot find a replacement.
    I would like to use an LED replacement, rewiring as necessary I think I need to
    (1) Join the former ballast connecting wires.
    (2) Remove the starter.
    This would in effect put 240V mains across two of the lamp pins, leaving the other two not connected. Is this correct? Do I need a fuse (LED starter) in series with the live wire?

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