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Compact Fluorescent Flashing.

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My friend still has a collection of compact fluorescent lamps. He has a coiled glass style one in his outside light fitting. It is time switch controlled. It was working well until.....wait for it.............wait for it. Today as it was getting dark and before it had switched on, it was gently strobing dimly. It was regularly lighting dimly and then turning off etc. I suppose the frequency was about 3 Hertz.


Has this strobing anything to do with me connecting up his main earth terminal to the official previously unused U.K.P.N. P.M.E. earth terminal? (All main bonding is in place).


Or, did I just not notice this strange strobing before?


Z.
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    damp, or possibly capacitive coupling if the permanent live and switched live run parallel for some distance.

    CFLs  do this if very small currents can flow in, and over several hundred cycles, that charge up the electronics that strikes and then runs flat and starts again.

    If it is annoying, one fix is to put a small C, about 100nF is enough, across the load, to make the voltage division such that it never reaches striking voltage.

    I also have had to do this for a boiler with a very meandering control circuit, that used to half heartedly fire its far too sensitive electronic ignition even when the thermostat said it should not.

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    It could just be damp in the electrics.  The most extreme case I have seen was a CFL at the end of a long damp tunnel.  When turned off, it would strobe brightly for several tens of seconds, before the strobing gradually dimmed to nothing.
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    The one above my bed does it, but I can see it only when my eyes have become dark-adapted.


    Try measuring the voltage across the pins with the switch in the off position. It may be surprisingly high - of the order of tens of volts. You can also measure the current which flows when the switch is off. IIRC, I found about 1 mA.
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    Thinking about it, it has only showed this strobing when a nearby light was left on, so it may be capacitive coupling due to parallel cable running. It is hardly noticeable except at low light levels.


    Z.
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    I remember sitting on a London Underground train some years and watching “black rings” rolling along inside the fluorescent lighting tubes. That was every lamp and only a couple had the tings going the opposite direction  to the majority.


    Andy B.
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    I have seen this phenomenon in linear fluorescents and on one occasion it was down to reverse polarity after a new meter was fitted.
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    I remember sitting on a London Underground train some years and watching “black rings” rolling along inside the fluorescent lighting tubes.




    Some of the older trains used to  run the tubes direct off the DC traction voltage. all the modern ones have a switched mode supply 'HF ballast'


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    A relative of mine has this effect on a landing light controlled by two-way switching. The house was built circa 1960 and lighting cables did not have earth conductors. The effect is caused by capacitative coupling across the conductors of the strapping cable. It sounds like something similar could be happening in your case, or, as others have suggested, dampness somewhere causing a high-resistance path.
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    All of the above can occur as mercury vapour lamps reach the end of their life, just before failing totally. I not sure, but I seem to remember it has something to do with the mercury vapour concentration gradually reducing due to it condensing into tiny droplets. You sometimes see these in failed lamps. I'm not sure why it condenses though....


    regards

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