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Strange electrical issue - any electricians or electrical engineers here

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70herald

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Discovered something very strange. A few days ago I put a little LED light in a wall sconce. It gives off a bit of light which is all I need, but strangely enough, when I turn it off it continues glowing, not on, but still slightly glowing.

So I checked voltages and discovered that there is 12v on the lamp even when turned off. Then I unplugged the LED lamp and the voltage on the circuit disappeared!

This was interested so I took a look at other bulbs on the same circuit and found that there was 45v (live side turned off to 0) across a CFL on the same circuit. When I unscrewed that bulb the voltage also vanished.

Since it the voltage vanishes when the bulb is disconnected I don't think it is a short?

The only thing that makes sense is that there must be inductance from the live wire in the same conduit, but how does it cause such high voltages, and enough current to partially light the LEDs? And how can I turn those LEDs off, it bugs me seeing them half on.
 
I'm not an electrician. I wonder though if there is a wall switch upstream of that outlet and the switch was wired to neutral instead of hot. That way, hot is always feeding electricity.
 
Just a WAG... is there a transformer built into the base of the bulb so it is "instant on"? I would think that LED's should come on instantly, but CFL's need time warm up time unless this is their solution for instant on... really, just a guess.
 
No transformer on the LED, I didn't take the CFL apart, but I don't think modern ones use transformers either. Its all electronic. The only think I could see on the LED circuit was a bridge rectifier and a few capacitors.

What is so weird is that I only measure voltage when the lamp is part of the circuit. As soon as I disconnect the bulb the voltage I measure drops to 0.
 
It's possible that you have an open neutral, and the second lamp is somehow completing the circuit via the ground. I had a similar situation recently. When I opened the refrigerator door and the light came on, a radio on the same circuit would come on. I thought the house was possessed. Thankfully my BIL, the electrician figured it out. We found a broken neutral wire in another box on the circuit. He said that those type of issues can cause fires.

It merits further investigation by a pro.
 
OK at home for the day with a sick kid, and lots of time to experiment.
I took an extension cord, disconnected the ground wire on the plug end and hooked up the LED between neutral and the no longer connected ground wire. Then I plugged it in and --- The LED weakly lights up, just like in the fixture. A quick check of the voltage also shows that it is identical to the voltage when it was in the fixture.

So apparently what happens is that the LED needs so little current to start lighting up that the induction between the always live supply line and the switched line between the bulb and the switch is enough to partially light the LEDs. Kind of neat.
 
I have (had) 20 strings of C9 LEDS on my old house.
All were running thru about 5 different timers.
On one timer it always had a slight glow to the lights in the off position.
For 5+ years I worked on this and never did find the cause.
I did some Google work and this is a known occurrence from LEDS
Check Google on it
 
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