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Thread: Faint glow with LED recessed cans

  1. #1
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    Nov 2007
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    Faint glow with LED recessed cans

    I recently finished a new build. Customer called and says that he has a room where the can lights have a faint glow when turned off.

    It's only noticeable with total darkness.

    This particular room has 8 of the total 70+ cans I installed. All of the trims are the same brand and model.

    I won't be going to look at the issue until Monday evening.

    I do know that the switch bank where the switch is located also has 2 Diva dimmers that are back lit devices.

    The can lights in question are controlled with a single pole switch. The 2 back lit dimmers are controlling other lighting.

    All lighting in that switchbox is fed from the same branch circuit.

    The only thing that's different from any other switching with all the other cans is the presence of the 2 backlit dimmers.

    Any help on what to look for would be appreciated.

  2. #2
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    If the dimmers don't have a neutral terminal, they are in series with, and thus powered through the load. Incandescents have low enough impedance to stay dark when in series with the dimmer illumination, but the LEDs' internal power supplies are apparently energized enough to slightly light up the LEDs. The solution is non-illuminated dimmers.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  3. #3
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    Even with the dimmers controlling totally different loads they are the cause?

  4. #4
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    I’ve seen lighted switches cause LED to stay on and lit up at a low level. Start with that.

  5. #5
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    Larrys post stated as much.

    I would not have thought that dimmers controlling other loads would cause the lights on a separate switch to still be getting a source of power.

    This forum is very helpful and informative

  6. #6
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    Quote Originally Posted by nizak View Post
    Even with the dimmers controlling totally different loads they are the cause?
    No, I didn't catch that. Troubleshooting is a process of elimination.

    In that case, I'd start by disconnecting the switched wire on the load side of the switch.

    Also, you could temporarily attach an incandescent bulb at one of the offending LED lights.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  7. #7
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    Placerville, CA, USA
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    Also turn off the breaker that is feeding the LEDs, and if it is a different breaker the one feeding the backlit dimmers.
    Possibly the interaction is happening because the lighted dimmers are feeding current to an EGC which is not solidly bonded to the neutral back at the panel. Energizing the EGC at a low level might cause reverse current through the EGC connection at the unlighted dimmer/switch for the can lights in question.

  8. #8
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    Quote Originally Posted by GoldDigger View Post
    Also turn off the breaker that is feeding the LEDs, and if it is a different breaker the one feeding the backlit dimmers.
    Possibly the interaction is happening because the lighted dimmers are feeding current to an EGC which is not solidly bonded to the neutral back at the panel. Energizing the EGC at a low level might cause reverse current through the EGC connection at the unlighted dimmer/switch for the can lights in question.
    OP stated all are on the same branch circuit. The switches are also in the same box.
    Cheers and Stay Safe,

    Marky the Sparky

  9. #9
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    The only thing that's different from any other switching with all the other cans is the presence of the 2 backlit dimmers.

    I would start by disconnecting them and seeing if the problem goes away.
    Cheers and Stay Safe,

    Marky the Sparky

  10. #10
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    Springfield, MA, USA
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    LEDs will illuminate with very little current flow. All of the shoplights that I've purchased from costco light up (very dimly; not even enough to bother me when sleeping but enough to see in a dark room) just from leakage across their built in switch.

    Question: the single pole switch feeding these lights, is it 'inline' with the circuit feeding the lights, or feeding by a 'switch loop'. My though is that if you have a 'switched hot' sitting in a cable next to an 'unswitched hot' then capacitive coupling between the wires might be enough to dimly illuminate the lights.

    Question: do the lights turn off completely if the breaker is opened?

    Question: is there a source of RF that might be powering the lights, eg a nearby radio tower?

    -Jon

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