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I've got a metal ceiling light chandelier thing which takes 4*G9 bulbs. I recently replaced the halogens with LEDs (specifically, http://ecotradeuk.co.uk/index.php/product/lumilife-5-watt-g9-led-bulb/)

The weird thing is, when the lights are switched off, the LEDs emit a very soft glow (but the Halogens didn't). Does that mean something is wrong with my wiring?

I'm in the UK, and the light is serviced by 2 switches. Also, if I turn off the main circuit breaker for the lighting, they do stop glowing.

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  • Are either of the switches "smart" switches?
    – Tester101
    Commented Feb 19, 2016 at 9:24
  • No, regular switches. Each of them switches 2 lights
    – xorsyst
    Commented Feb 19, 2016 at 9:26
  • You might possibly have a switched neutral.
    – NKY Homesteading
    Commented Feb 19, 2016 at 12:00
  • @JasonWhipple, could you expand on that in an answer - how would I tell, what's the fix? Could it just be that the light fitting live and neutral are the wrong way around, or something in the switches?
    – xorsyst
    Commented Feb 19, 2016 at 12:25
  • I saw this problem before within the last month, possibly also in the UK. I don't recall what the answer was.
    – Harper - Reinstate Monica
    Commented Feb 20, 2016 at 0:58

2 Answers 2

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You have something else in the circuit that uses a small amount of power and which bypasses the switch.

A smart-switch of some sort will do this but there are other devices that also do this, for example a switch illuminator (so you can find it in the dark)

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The issue here is that, at switch locations you generally do not have neutral present. Just live and switched live (and earth). So the illuminator cannot be wired in parallel but mus be in series with the lighting circuit. When you turn the switch on, it turns the illuminator off because the switch shorts the illuminator so that there is no longer a potential difference across it.

These things pass a very small current, at lower voltage, through the rest of the circuit. This is insufficient to make incandescent or halogen bulbs glow, but is enough for some LED driver circuits to start to work.

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  • This certainly sounds feasible - but I don't think I do! Is there an easy way to track down what's doing this with a multimeter or similar?
    – xorsyst
    Commented Feb 19, 2016 at 9:50
  • @xorsyst: If your multimeter is Cat-II rated (or better) and has probes rated for >250V and has shielded probe-tips, you could use it to measure the AC voltage at the light fitting with the switch off and the current passing through the light fitting with the switch off. Neons used to illuminate switches typically drop about 70V I think so I'd expect to see 230V-70V=160V at the light fitting. I think the current would be a few tens of milliamps for a neon illuminator. Tracking it down will be tedious (and potentially lethal, so take care).
    – RedGrittyBrick
    Commented Feb 19, 2016 at 9:56
  • Could it be something on a completely different light in a different room? I'm thinking perhaps my bathroom extractor fan
    – xorsyst
    Commented Feb 19, 2016 at 10:15
  • @xorsyst: In a conventionally wired standard-sized home, all lights on one floor are part of the same circuit. However each light typically has it's live wire independently switched at one point. Hallway and stair lights may have two-way switches. So unless there is a wiring fault, your bathroom extractor fan should not be able to bypass the switch in a different room.
    – RedGrittyBrick
    Commented Feb 19, 2016 at 10:23
  • If the fan is a later addition to the house, it is possible whoever fitted it picked up power not from the bathroom ceiling-rose/junction-box (etc) but from that of an adjacent room that was more conveniently located or more accessible (typically in the roof space). It isn't immediately obvious to me how this could be miswired to produce the effect you describe but it may be a possibility. Fans often have a run-on facility (e.g. 10 mins after lights turned off) that require a permanent-live as well as a switched live - so there is scope for doing something silly.
    – RedGrittyBrick
    Commented Feb 19, 2016 at 10:27
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Electroboom answered this well in a youtube video https://www.youtube.com/watch?v=_bgUy6zA0ts

It's basically using the switch wiring as a capacitor, and is not a wiring fault.

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