Lightbulb Conundrum - Drinks, Anyone?

Technical
2006-11-08

A pint is yours if you can solve this conundrum for me (a theoretical explanation you can convince me of will do; I have a practical workaround).

A few weeks ago I replaced some of the bulbs in my house with energy-saving ones. However, the ceiling light in my hall behaves in a very odd manner. Occasionally, after I switch it off at the wall, it flickers on very briefly (for about 1/10 second) about once every minute - even though the power is (allegedly) off. The flicker is fairly dim, so I only notice it at night. If I take the bulb out of the socket, the flicker stops. If I put it back, it starts again. This behaviour happily continues for hours - to the extent that I remove the bulb when it happens because it’s too distracting when trying to sleep.

Perhaps it’s some kind of residual charge in the bulb. But this doesn’t really seem to explain why it only flickers when the bulb is in the socket (even though the switch is off). It also doesn’t explain why it doesn’t happen in the rest of the house (they have the same brand of bulb). The only difference is that the hall has two switches - but they aren’t dimmer switches or anything special.

Any thoughts?

Comments

After reading this I agree with the Capacitance idea. I have installed 4 energy saver bulbs into our house. 3 out of 4 are flickering and these 3 are on 2 way switches. No powerlines near here and these lights are towards the rear of the house so no main feeder lines nearby. I am glad I found that others are having this problem. I was starting to worry about defective wiring in the house.
— Glen 2007-12-19 13:57
Hi there. I know it's already a year ago that you had this problem, however I had just the same and I found what causes it. I was trying to find some information online, but I couldn't find anything other than your site, so I hope other people can find this useful... Now. Yes, it is the switch. When I started having that problem, I put the bulb in another socket where the switches are like 30 years old, very simple switches and there was no flickering whatsoever. On my newer switches I've got a little red light indicating where the switch is in the dark, I've noticed that whenever I have a flicker in the bulb this little red lamp also flickers. I removed the light indicator and here we go - no flickering! Just like somebody esle commented the incandescent lamps need a lot more energy to heat up enough as to give light but the CFLs would light up even with less energy, which is apparently the energy for the little red lamp indicator on my switch, collected in the capacitors of the ballast. I hope thit helps. Cheers
— Vincent 2007-12-09 10:20
One of our energy saver globes has developed a flicker after being turned off but I am reasonably sure this was not present when first installed. Is this flicker in any way dangerous? We never had any trouble with the old style globes.
— June T 2007-11-27 19:05
forgot to say there also must have been reverse polarity at the fan for this theory to be possible ????? I think????
— Mick in Cairns 2007-09-03 14:06
Maybe Warwick is right but ! I am an electrician and came across an identical problem with a 14 watt energy saver. I re-wired the circuit and changed the switch but still the same problem. Is there an old ceiling fan in the room ? The only answer I could come up with was that the fan capacitor was periodically feeding back through the neutral, the cost didn't warrant any further investigation and the house owner decided to put an old bulb back in. He liked the fan so I didn't replace it to see if a new fan would have solved the problem...????
— Mick in Cairns 2007-09-03 14:03
I too had a problem with flickering when replacing old incandescent light bulbs with the new energy saving fluorescent bulbs. After having tested every possible part of the circuitry the fault was finally located in cable connecting the light fitting to the switch. There appeared to be nothing wrong with the cable except that the active and neutral wires were both enclosed in the same sheath. Replacing the twin cable with two single insulated wires solved the problem. I can only put the problem down to a capacitive effect between the cables causing a voltage potential across the bulb.
— Warwick 2007-05-12 04:23
Worry not ... You are not alone. I have a energy saver bulb that is just as lively. I asked my brother-in-law - who is a lecturer in electrical engineering. He looked at me puzzled and suggested it was supernatural and to get an exorcist in ... Seriously, if I get a straight answer out of him I will post it.
— Daddynocred 2006-12-27 21:22
I would suggest that your flicker is due to the capacitance of the wiring and across the contacts. Some methods of wiring two way switches, result in more capacitance than others and are more likely to cause this problem. If this problem is on a two way switch, you could transfer the bulb to a one way switched socket and see if the problem transfers.
— DaveB 2006-12-19 19:51
The bulb definitely stops flickering when removed. It starts again if replaced within an hour or so.
— andrewferrier 2006-11-13 11:27
Good point. That can of course be easily verified by taking the bulb out and seeing if it still flickers. I am not sure if orientation affects the flicker, but it probably will...
— Anton Piatek 2006-11-13 08:35
"I recon it has to be the switch" I suspect you'll be proved to be correct but as the link below suggests, it is entirely possible to make a flourescent tube flicker with no wire attached to it: http://news.bbc.co.uk/1/hi/england/bristol/3509651.stm
— Richard G Brown 2006-11-10 09:32
It is not the bulb. With no power, a bulb should never flicker no matter how faulty it is. It *could* be the live wire, but I would be very surprised to see a bulb flickering with no return wire... I recon it has to be the switch, if you get a multimeter and are comfortable with doing it, test the light socket for power when the switches are off. I expect you will find a smallish amount of power trickling through.
— Anton Piatek 2006-11-10 08:33
OK, all of those sound like plausible explanations, guys. I should probably come clean at this point and say that I rent this flat, so I'm not going to tinker with it too much by pulling things out of the wall - although the 'correct' fix of getting an electrician round sounds like too much hassle. I'll give the multimeter a go next time I see a sale in Robert Dyas (which would be next time I walk past it, as they've always got a sale on). I think a pint each in the meantime would only be fair - next time we're in the same drinking establishment :) I have to admit though, Richard, I hadn't tried that obvious diagnostic technique of swapping the bulbs. I hang my head in shame at my lack of troubleshooting skills :( I'll give it a go next time the problem rears its head.
— andrewferrier 2006-11-08 21:39
You don't have a ring main directly above or anything else that might create a magnetic field, do you? I'm sure I've seen examples of flourescent tubes lighting up when placed under power-lines, for example. Alternatively, is it possible that the hall light switch is wired the wrong way round (so that it isn't the live wire that is controlled by the switch?) I don't suggest you test by sticking your finger in the light fitting and I'm not sure how it would explain the phenomenon but it strikes me that we need to find something that differentiates this light fitting from any others. (I assume you've tried moving the bulbs around to confirm it is the fitting and not the bulb?)
— Richard G Brown 2006-11-08 17:42
Sounds like your switch has dodgy contacts and is letting some current through. If you are feeling brave you could test for live electricity with a multimeter or electricians screwdriver (the kind with a light). Or you could take the switch off the wall and test that. To be honest, I would buy a new wall switch (or two in this case) from B&Q, turn off the mains and swap both. See if that fixes it. I would not like to be playing with live mains, and the cost of 2 switches is only a few quit. In case you are wondering why it doesnt happen with incandescent bulbs, fluorescent ones have inverters with capacitors (i believe) which could explain the flickering, whereas a normal bulb does not get enough power to light up, so just produces a little heat instead
— Anton Piatek 2006-11-08 13:22