LED light doesn't go completely off

[MyNameIsUrl]

I have an LED bulkhead light inside a cupboard, with a switch outside the door. Recently it failed but isn't completely dead, it still lights faintly. The strange thing is when switched off it still glows extremely faintly.

I wondered if there could be some current going through it when switched off, and I confirmed it's still live inside when the switch is off. (I used a non-contact tester pen to show it's live.)

I looked at the switch and there are two twin-and-earth cables in the box - the installation was after the original housebuild - and I assume one cable is dropped from the lighting circuit in the ceiling void, and the other goes to the light fitting which is only a couple of feet away from the switch inside the cupboard. The thing that looks strange to me though is that the switch is connected across the two black wires, and the two red wires are connected together in a domino connector block.

What's going on here? Should I just replace the light fitting (with the power off at the mains)? Or is there something happening beyond my understanding?

[Urbandreamer]

I have an LED bulkhead light inside a cupboard, with a switch outside the door. Recently it failed but isn't completely dead, it still lights faintly. The strange thing is when switched off it still glows extremely faintly.

I wondered if there could be some current going through it when switched off, and I confirmed it's still live inside when the switch is off. (I used a non-contact tester pen to show it's live.)

I looked at the switch and there are two twin-and-earth cables in the box - the installation was after the original housebuild - and I assume one cable is dropped from the lighting circuit in the ceiling void, and the other goes to the light fitting which is only a couple of feet away from the switch inside the cupboard. The thing that looks strange to me though is that the switch is connected across the two black wires, and the two red wires are connected together in a domino connector block.

What's going on here? Should I just replace the light fitting (with the power off at the mains)? Or is there something happening beyond my understanding?

The answer is simple, you have a ghost!

Alright, it's probably not a ghost. LED lights are not simple things. They are actually a current regulated AC-DC convertor with a deliberate leakage resistor.
The mains charges a capacitor which powers the LED. When you disconnect the mains the capacitor discharges through a leakage resistor.
When LED lights fail, it's often the AC-DC convertor. It looks like the solder connection to your leakage resistor is one of the parts that has failed. Hence the remaining charge powers the LED for significant time.

As for the wiring, it sounds sort of right, though coloured sleeves should have been fitted. Mains goes to the rose/fitting. The live is connected to the red wire of another twin and earth that goes to the switch. The switch connects that to the other insulated wire (black) that should be sleeved in red to indicate that it could be live. The other end at the fitting should also be sleeved red, but is connected to the bulb. The return from the bulb is connected to the neutral.

[Mike4]

Not an answer to your question but I was about to start a similarly-titled thread!

My own LED bulkhead lamp in the conservatory works fine, but like yours, when turned off still glows faintly. This is obvious at night when it bathes the conservatory in what at a casual glance looks like moonlight. Even when there is no moon!

I too wonder what is going on. I have an electronic timer switch on it which I wonder is leaking current, or whether there is some sort of referred voltage keeping it energised.

[Gerry557]

I think it might be a faulty switch.

With mains off disconnect and then with the disconnected wires in a safe condition put the mains back on and check the light is firmly off.

Make sure to switch the mains off again to put it back together.

[bungeejumper]

I have an LED bulkhead light inside a cupboard, with a switch outside the door. Recently it failed but isn't completely dead, it still lights faintly. The strange thing is when switched off it still glows extremely faintly.

I wondered if there could be some current going through it when switched off, and I confirmed it's still live inside when the switch is off. (I used a non-contact tester pen to show it's live.)

Sounds familiar. I was recently testing the electrics behind an old light switch fitting which had been removed (and safely terminated and covered with a blanking plate). And much to my surprise, it was delivering a current of about 50 volts! (Apparently at very low amps, although I didn't have the technical expertise to measure it. I never did really get the hang of my digital multimeter. )

It didn't take me very long to read that this sort of "empathetic leakage" can happen when cables are bundled together in great sheafs. For some reason, Americans with their 110V systems seem to complain about it more often than us Brits. I'm sure that others with more physics in them than me will remember what the phenomenon is called?

BJ

[MyNameIsUrl]

As for the wiring, it sounds sort of right, though coloured sleeves should have been fitted. Mains goes to the rose/fitting. The live is connected to the red wire of another twin and earth that goes to the switch. The switch connects that to the other insulated wire (black) that should be sleeved in red to indicate that it could be live. The other end at the fitting should also be sleeved red, but is connected to the bulb. The return from the bulb is connected to the neutral.

Yes, I follow what you're saying, which is what I understand is how normal ceiling lights operate - there is live at each ceiling rose, and a single cable at the switch which connects live to the red-sleeved black wire. In this arrangement, with a ceiling rose and pendant the rose is always live, but the pendant shouldn't be live when the switch is off. In my situation, the light is live in just the same way, but as it's at shoulder height in the cupboard that's causing me to feel a little different about it. I think from what you say the two-wires-in-the-switch, one-wire-in-the-light approach might be a little unusual.

[9873210]

I have an LED bulkhead light inside a cupboard, with a switch outside the door. Recently it failed but isn't completely dead, it still lights faintly. The strange thing is when switched off it still glows extremely faintly.

Most, but not all, LED bulbs glow extremely faintly for some minutes after they are turned off. These bulbs use phosphors to convert blue light to other colors to get a broader spectrum. The phosphors store a little bit of energy and continue to glow after the LED proper stops emitting blue light.

Usually you do not notice this afterglow, but if this particular LED is in a very dark closet or you are paying particular attention to it you might think it is acting differently than others. Might try using putting the same bulb in a portable lamp (e.g. a work light) in the same location and see if you get the same glow when it's unplugged.

[Spot5]

This happened to me a while ago.
It turned out to be leakage in the cable.
Have you got old rubber wiring anywhere?

Regards,
S

[csearle]

What's going on here?

I suspect you have a polarity issue.

If the light switch is switching neutral rather than line then the light fitting will always have 240V (w.r.t. Earth) connected to it even when switched off!

I'd establish first whether this is perhaps the case before doing anything else.

Chris.

[jfgw]

I suspect you have a polarity issue.

I would certainly agree with that. I can't think why a switch would be between two black wires.

LEDs require knickers-all current to glow faintly. I recall fitting an outdoor light switch with a neon lamp. These neon lamps have a resistor in series which I think is about 330k. These are usually wired across the switch such that, when the switch is off, the neon lamp (with its resistor) and the thing being switched are in series across the mains. A tiny amount of current flows which is enough to light the neon lamp but is not usually enough to affect whatever is being switched. In this case, however, the glow from the outdoor light (an LED floodlight) was very noticeable, even in daylight. Disconnecting the neon lamp solved the issue.

There will be some leakage in the cable and, if the neutral is switched, leakage between earth and the neutral after the switch will allow current to pass. There will always be a very small amount of leakage due to capacitance but I would not have thought that this would be enough to be noticeable. You did say that it glows extremely faintly, however.

If the switch is in the neutral, I suspect that correcting this so that the switch is in the line will stop the cupboard light from glowing when it should be off.


Julian F. G. W.

[gryffron]

What's going on here?

I suspect you have a polarity issue.
If the light switch is switching neutral rather than line then the light fitting will always have 240V (w.r.t. Earth) connected to it even when switched off!
I'd establish first whether this is perhaps the case before doing anything else.

If switching the power off at the fuse box immediately cures the glow. Then this would hint very strongly at a switched neutral problem. Which should be fixed as it is pretty dangerous.

If it continues to glow even with the mains off, that would hint at one of the earlier suggested issues.

Gryff