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Upgrade a Circline fluorescent lamp

While sitting at my desk I noticed a humming sound from the floorboards underneath my chair: it was the circular fluorescent light in the room below. The ballast unit in the ceiling light was buzzing and this could be heard downstairs as well as in the room above. I also had the nagging problem of the fluorescent light strobing several times, with several seconds of darkness before finally starting up. This had become a nuisance over the years, so much so that people would stumble around in the dark, which had caused at least one injury accident.

Upgrading the lamp is one answer but sometimes it’s not feasible or practical just to replace light fittings with modern halogen downlighters or LED bulbs, and if anything it can be a costly and wasteful exercise especially if it’s just in a utility room or cellar. I found circular fluorescent lamp fixtures are all but obsolete now, as everyone is switching to downlighters. Instead of raving around making big holes in the ceiling and trying to run wires everywhere, there is also the likely cost and payback time for an upgrade. As a long term proposition, LED bulbs or maybe CFLs are the way to go, and (thanks to the EU) halogen bulbs themselves are already being phased out. Until then I wanted to get a bit more life out of the circular light fitting, and as long as I can get new tubes I’m happy to do that.

Fluorescent tube apart, instead of struggling with old 1960’s tech, it’s straightforward to give a Circline circular light a new lease of life by upgrading the old-fashioned, noisy electrical gear with an electronic unit instead. They are cheap enough, very small and lightweight in comparison with a traditional ballast, and are rated up to 40W maximum (hence the 0.19 amps rating). So a 40W-rated electronic unit will be fine for my 32W tube. The other key benefit is that electronic ballasts are instant-on, with no flashing or buzzing, although you might have to accept a slightly lower light output (say 10% reduction).

DIY Instructions to upgrade a Circline circular fluorescent light

Any DIYer can install an electronic ballast and upgrade a typical 32W or 40W Circline circular fluorescent light unit. My own light unit had two wall switches and was an Italian-made lamp marketed by Ring in the UK, probably 15 years+ old and it’s likely that the wiring for yours will be no more complicated than mine, and possibly simpler.

Original Circline lamp fixture and wiring [click to see]

First, it’s essential to switch off the lighting circuit at the fusebox and double check that everything is isolated before doing (or touching) anything: ideally use a contactless mains detector on the light’s wiring if you have one. That’s because some light circuitry wiring can be permanently live. Switching off the light switch(es) isn’t good enough. So make sure you either pull the fuse or switch off the circuit breaker and double check that it’s all turned off, using a tester if possible. I found neon screwdriver mains checkers tripped the circuit breakers due to leakage current, but the contactless C&K type with LED and beeper that I used was fine.

Testing to ensure the mains is switched off [click to see]It’s a good idea to photograph the lamp’s wiring using a smartphone for reference. With the mains isolated, look closely at the existing wiring and identify the mains Live (L), Neutral (N) and Earth (E) feeds that probably go to a screw terminal block. Multiple wires might go into one terminal and several live wires might be joined together (part of the ring mains wiring) which should not be altered.

Old fluorescent light wiring [click to see]Live wires going into the terminal block might be brown or more probably black with a red sleeve. This live wire must not be confused with an ordinary black (Neutral) wire.

  • As shown in my photo, there was a fault with my existing wiring: the red sleeve was missing, but the black wire is LIVE INPUT. I added a red sleeve straight away.

Unplug the fluorescent tube by pulling off the 4-pin plug and put the tube aside for now. You can then unscrew the terminal block screws to loosen the mains L, N, E input wires. As the existing push-fit/ screw terminal block could not be re-used I fitted a new one. Then re-wire L, N and E inputs to the new block.

The terminal block might need unscrewing from the metal baseplate. Also remove the starter (the small cylinder with two wires). It rotates and pulls off, then prise the base off the light unit. The old ballast unit can then be unscrewed (it’s heavy) and the whole assembly should come away.

The new electronic ballast is much smaller and lighter and can be fitted to the metal base using one screw from the old ballast (do not overtighten). The unit’s Live (red) and Neutral (white) wires can be connected to the L & N feeds of the (new) screw terminal block.

New electronic ballast wired, with new terminal block and earth wire [click to see]It is essential that the lamp remains properly earthed after the upgrade. Earth wires are usually bare copper, and should be sleeved with green & yellow tubing. I clamped a solid, sleeved earth wire under the mounting screw of the old terminal block screwed onto the light fitting’s metal base, and connected the wire to the Earth terminal of the new screw terminal block. Thus the light fitting’s metal base was earthed properly.

Refit the fluorescent tube and connect up the new electronic inverter. Shuffle the tube around if the connector doesn’t quite reach. Fit the lamp diffuser and switch on the mains – you’ll find the lamp will now light instantly with none of the fuss and bother of the old unit.

Tube running with new electronic ballast [click to see]I intend to do the same with a kitchen lamp too. Here’s a suitable electronic ballast, and as they’re so cheap maybe keep one for spare. A good quality C&K non-contact tester (T2272A) is also shown. It has red-green LED and audible buzzer indication of live wires, without needing to touch them directly.