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James_From_Canb

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Joined: 19/06/2011
Location: Australia
Posts: 265

Posted: 01:28am 16 May 2012

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Hi.

I recently bought a pair of home brand 100W equivalent spiral mini fluoro bulbs from a large supermarket chain and put one in my son's room. After he turned the light off it flickered every 30 seconds or so, at the top of the bulb. He got around the problem by removing the bulb each night. I tried the other bulb and it did the same thing.

I had an electrician check the circuit. He disconnected the fader on the switch, but it still flickered. He reckoned that there was nothing wrong with the circuit.

I tried the bulb in another room and it did the same thing.

I could understand one flicker as a capacitor discharged, but not multiple flickers.

Any idea what could be going on?

Thanks

James

My mind is aglow with whirling, transient nodes of thought careening through a cosmic vapor of invention.

Hedley Lamarr, Blazing Saddles (1974)

yahoo2

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Joined: 05/04/2011
Location: Australia
Posts: 1166

Posted: 02:26am 28 May 2012

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quote from silicon chip magazine may 2007

Comment: we recently observed the flashing CFL effect ourselves in a number of lamp fittings. We have concluded that it is not a fault in the CFL or the 240VAC wiring but an artefact of the capacitance of the wiring to the light switch (from the ceiling junction box). In a typical home, this will be about six to eight metres of sheathed twin cable and this can be expected to have a capacitance of maybe 300pF or more.

In effect, this cable capacitance across the switch lets the CFL bridge rectifier build up sufficient DC to let the circuit fire the CFL tube, collapsing the DC and letting the cycle repeat ad infinitum. It is acting as a relaxation oscillator.

While you are aware of the flashing effect only at night, it happens all the time. If it worries you, it could be stopped by connecting a small capacitor across the CFL socket, say .01mF (10nF) 250VAC class X2. Alternatively, the effect could probably be stopped if the cable to the switch was changed to "twin and earth".

This leakage capacitance effect also occurs with incandescent lamps (and any other load for that matter) but it is of academic interest only.

I'm confused, no wait... maybe I'm not...

James_From_Canb

Senior Member

Joined: 19/06/2011
Location: Australia
Posts: 265

Posted: 01:49pm 28 May 2012

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Many thanks.

I returned the bulbs to the supermarket and bought the more expensive 'name brand' ones. They don't flicker, and my son is much happier.

Again, thanks for the explanation.

Regards

James

My mind is aglow with whirling, transient nodes of thought careening through a cosmic vapor of invention.

Hedley Lamarr, Blazing Saddles (1974)

yahoo2

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Joined: 05/04/2011
Location: Australia
Posts: 1166

Posted: 09:22pm 29 May 2012

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I do wonder about the quality of some of the bulbs sold at large supermarket chains.

I recently purchased a couple of halogen bulbs. Not only did they have bits of flux around the B22 terminals causing corrosion, the halogen element has no UV filtering built into the glass. Using a globe like this in a reading lamp is just asking for skin cancer.

The worst thing is I can buy a quality name brand halogenGLS bulb with UV cut, for half the price that I paid

The LED globes cant come soon enough, CFL's are a pain.

I'm confused, no wait... maybe I'm not...

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