ceiling light flashes

Discussion in 'General Electronics Chat' started by 0001T, Jul 21, 2009.

  1. 0001T

    Thread Starter Member

    Feb 28, 2007
    i am facing this tricky little problem now:mad:

    the ceiling light in my room flashes even though the switch has been off.
    usually notice this during bedtime when i am lying down facing the ceiling. it will flash. is this some kind of 'residual charge' or something like that:confused:

    anyone has experienced this also?
    how can i go about solving this issue?

    thanks a million
  2. Von

    Active Member

    Oct 29, 2008
    What type of lamp.. fluorescent or incandescent?
  3. 0001T

    Thread Starter Member

    Feb 28, 2007
    its flourescent. thks
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    And does it flash a few times and stop, or flash all night?
  5. 0001T

    Thread Starter Member

    Feb 28, 2007
    it will flash & stop, not continuously flashing. it is still on the next day. but i did not monitor throughout the nite cos most of the time i will doze off to dreamland:D

  6. mentaaal

    Senior Member

    Oct 17, 2005
    is it possible that you could have a dodgy switch? does the light ever flash when the switch is on? seems the most likely cause of the problem is the switch... you could try flicking the switch when it is off and see if does anything?
  7. RiJoRI

    Well-Known Member

    Aug 15, 2007
    This is known to occur with CFL lights. I googled "cfl flash" and found some info.

    (fluorescent lights give me depression!)
  8. studiot

    AAC Fanatic!

    Nov 9, 2007
    I think you should have the neutral checked as it can reach several tens of volts (more if faulty) above earth, though I have never heard of it being enough to overcome a flourescent striking voltage.
  9. 0001T

    Thread Starter Member

    Feb 28, 2007
    thanks to all who replied. now with some leads...will check again
  10. millwood


    the wiring is faulty.
  11. Tesla23

    Senior Member

    May 10, 2009
    It sounds like a commonly observed effect with some CFLs. see for example :

    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.
  12. BillB3857

    AAC Fanatic!

    Feb 28, 2009
    Do you live near an airport? Radar can light off fluorescent lights.