LED glows when off

Discussion in 'General Electronics Chat' started by andrew24, Oct 1, 2010.

  1. andrew24

    Thread Starter Active Member

    Aug 20, 2008
    76
    0
  2. Nik

    Well-Known Member

    May 20, 2006
    55
    3
    Check your insulation !!
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Probably for the same reason a neon lamp glows when it is connected to hot (and nothing else). LEDs respond to very low levels of current, the kind of current you might get when there is a slight capacitive coupling to earth (which is pretty much everywhere). Sometimes electronics isn't as straightforward as it seems.

    Is it so bright as to need fixing? If so Nik is probably right, you have other issues.
     
  4. andrew24

    Thread Starter Active Member

    Aug 20, 2008
    76
    0
    Yes it's noticable even in the daytime. I've found that some people suggested connecting a capacitor across the lamp terminals and that actually helped.. But how?
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    It is responding to radiated energy, possibly 60Hz, possibly RF from a local radio station (I'm betting line frequency). A capacitor will divert the energy around the LED.

    Where did you get the bulb?
     
  6. andrew24

    Thread Starter Active Member

    Aug 20, 2008
    76
    0
    you mean there is a capacitive coupling between the hot and other wire and that lets a small current to flow to the LED bulb? I measured the voltage across the bulb and that's 20V.

    The bulb is something like the one shown in the link: 2W 220V:)
    http://cdn2.ioffer.com/img/item/162/652/362/p8I3.jpg
     
  7. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Well, putting a resistor parallel might help, but I'd recommend highly against. It would use electricity, generate heat, and kill a lot of the advantages of using an LED, not to mention have you messing around with line current.

    Is one of the two off switch positions better than the other?

    You could also put a large coil in series with the light to see if that helps.
     
  8. andrew24

    Thread Starter Active Member

    Aug 20, 2008
    76
    0
    yes.. one switch position is definitely better than another, what does that mean?
     
  9. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    The brighter side is when the LED is connected to the hot side. The fact it is lighting connected to neutral hints there is a strong EMF in your house.
     
  10. andrew24

    Thread Starter Active Member

    Aug 20, 2008
    76
    0
    what could be the possible sources of this EMF? there is an elevator near..
     
  11. roadey_carl

    Active Member

    Jun 5, 2009
    116
    5
    its to do with EMF's. all the cables in your house are probably run quite close together... in fact, if you isolate the lighting circuit and test the cable I bet you get more then 12v showing.
     
    Last edited: Oct 1, 2010
  12. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    It is actually pretty normal. All house wiring tends to act like an antenna, transmitting as well as receiving. LEDs don't require much to generate light, just like neon bulbs. A common electricians tool is a neon screwdriver, if it touches a hot wire (with only one connection) it glows.

    You might try a 150KΩ ¼W resistor in parallel with the lamp, if that doesn't work I don't have much else to suggest. It is inherent of the LED and that section of wiring.
     
  13. andrew24

    Thread Starter Active Member

    Aug 20, 2008
    76
    0
    but what about a capacitor instead of a resistor?
     
  14. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    More or less the same thing, as is the coil in series. We just looking for ways to suppress stray signals around the LED. The resistor (or capacitor) will drop the voltages around the LED directly by loading what is basically an incredibly weak signal.

    I calculated around 0.1W for 120VAC. You might try it before the cap, the values make a difference here, and you don't want to waste the electricity the LED saves.
     
  15. andrew24

    Thread Starter Active Member

    Aug 20, 2008
    76
    0
    Thank you ;)
     
  16. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    Two switches as in a three-way switch. Worse under one condition than the other.

    Chances are the insulation in one of your switches (or the wiring between them) is starting to break down.

    If enough current is getting through to light that bulb and you don't feel confident changing out the switches I'd get it looked into by an electrician, any leakage current that high could be the sign of an impending fire hazard.
     
Loading...