LED spot light dim glow when off

frank999 · 6 May 2021

Hi,

I recently had to replace an LED spot light, just a cheapo one from SF (not LAP though !):

https://www.screwfix.com/p/luceco-slimline-led-floodlight-black-10w-1050lm/714kj

I have an outbuilding, SWA runs from a House CU for approx 10-15 mts, terminating in a wiska box in the outbuilding.

Running from a spur on a single pole socket in the outbuilding, when turned off, and it was dark, you could see the LEDs glowing very very dimly. It would turn on OK at the switch. After about18 months the lioght failed to operate at the switch.

Could there be any form of induction or other way that power is leaking. I have checked the voltages coming into the outbuilding, and there appears no leak across N and earth. Polarity all looks good.

I have a new light I need to fit, I should fit that - could it be a duff light ?

Bit miffed if anyone can help.
Thanks

Taylortwocities · 6 May 2021

Probably induced voltage. It doesn’t take much for a LED to glow. You’ll probably find that a change to a better make of lamp will fix the problem.

some lamps (esp budget makes) need a snubber installed to reduce this problem.

bernardgreen · 6 May 2021

There is capacitive coupling between Live and Switched Live in the wiring to the switch, this allows a small amount of power to bypass the switch ( when OFF ) and an LED lamp can glow on this small amount of power.

This leaked power can be absorbed by a snubber connected across the lamp

Capacitor 0.047uF micro Farads 250 volts AC in series with Resistor 100 ohms

Which come pre-packaged as a contact suppressor from RS Components.

As a contact suppressor it would be fitted between Live and Switched Live at the switch BUT as a snubber it has to be fitted between Switched Live and Neutral at the lamp..

( If there is a Neutral at the switch it may be more convenient ( space wise ) to fit it in the back box of the switch )

KEMET RC Capacitor 470nF 100Ω Tolerance ±20% 250 V ac, 630 V dc 1-way Through Hole PMR209 Series
RS Stock No. 206-7869
Manufacturer Evox-Rifa
Manufacturers Part No. PMR209ME6470M100R30

There are other sources

Read more: https://www.diynot.com/diy/threads/...till-glow-when-isolated.555283/#ixzz6u5dSjCok

frank999 · 6 May 2021

Thanks for this info, very helpful.

This glow would not have occurred with old incandescents, as the current draw required was higher to make the element glow - where as LED's will illuminate (glow) on a far lower current.

I have previously had a leak in the outbuilding - which has been fixed, but wondered if this was related - but see that is not the case.

TimboTwo · 6 May 2021

I have the same problem with the 4 downlights in my bathroom. Can't be bothered to do anything about it.

frank999 · 7 May 2021

I had a feeling the unit would fail, and fail it did, and it was the all in one type, very wasteful.

What is this 'capacitive coupling' - is not a contact in a switch either on (240v) or not (0v)

Are LED lights - if tickled with a very low current from the capacitive coupling, prone to premature failure ? seems a poor design to sell these things without anything built in to deal with any encountered 'capacitive coupling'.

ericmark · 7 May 2021

Your thinking DC but the supply in your home is AC and so you can get inductive and capacitive linking in the cables, I got a load capacitor from CEF but most electrical whole sale outlets have them This one from Screwfix

JohnW2 · 7 May 2021

frank999 said:
What is this 'capacitive coupling' - is not a contact in a switch either on (240v) or not (0v)

'Capacitive coupling' exists between any two objects which are in proximity to one another. In the context we are discussing, although there will be a very small amount of 'capacitive coupling' between the contacts of a switch (when it is 'off'), more important is the 'capacitive coupling' between wires in cables in the lighting circuit.

With alternating current electricity, very small amounts of current can flow through this 'capacitive coupling' (potentially enough to make an LED flicker). A good example is seen in the infamous 'neon test screwdrivers'. If you touch one onto 230V,the neon should not light, since the other side of the neone is not connected to anything (as if there were a switch which were 'off'). However, if one touches the other end of the screwdriver, then the 'capacitive coupling' between one's body and 'the earth' (which is roughly at "0V") 'completes the circuit' and allows the neon to light up.

frank999 said:
Are LED lights - if tickled with a very low current from the capacitive coupling, prone to fail then ?

I would imagine that any such tendency would be trivial. Whilst one can obviously be unlucky, in general ('on average') LEDs, even those which 'flicker when off' last very much longer than traditional ('incandescent') light bulbs.

Kind Regards, John

frank999 · 7 May 2021

Thanks for those explanations, very helpful.
Could 'capacitive coupling' be described as a 'leak' of current, between the Live and Earth - at very high voltages you get an arc across a gap, and a 2Kw heater plugged into an uncoiled extension lead will heat up - in extreme cases melt the casing.

Whilst one can obviously be unlucky - would it shorten the normally expect life of an LED.

davelx · 7 May 2021

frank999 said:
and a 2Kw heater plugged into an uncoiled extension lead will heat up - in extreme cases melt the casing.
.

That's just down to the resistance of the extension lead, which causes power to be lost into the surroundings as heat. With the cable unwound, that heat dissipates into the surroundings and the temperature does not rise that much. When the cable is coiled up the heat cannot escape so fast, so the temperature rises, sometimes high enough to melt the cable & drum etc.

JohnW2 · 7 May 2021

frank999 said:
Thanks for those explanations, very helpful. Could 'capacitive coupling' be described as a 'leak' of current, between the Live and Earth ...

Sort of - a 'leak' of current between live and anything else - in the case we're talking about, probably a 'leak' between a wire in a cable which is at 230V and a wire in a cable feeding the LED.

frank999 said:
- at very high voltages you get an arc across a gap, and a 2Kw heater plugged into an uncoiled extension lead will heat up - in extreme cases melt the casing.

Arcs and the overheating of coiled-up cables are both totally different issues from 'capacitive coupling'.

frank999 said:
Whilst one can obviously be unlucky - would it shorten the normally expect life of an LED.

What I meant about 'unlucky' was that a few LEDs (like traditional light bulbs, and many other things) do fail early. However, if you had, say 100 LEDs in service, I doubt that the phenomenon we are talking about would make any difference to how long (how many years) it would be before 50 of them died.

Kind Regards, John

frank999 · 7 May 2021

Thanks, some Googling on Capacative Coupling ... finds him again, sure I'd seen something about this a while before:

https://www.davidsavery.com/index.p...when-off?responsivizer_template=responsivizer

Some bed time viewing ...

£5.76 for a 'corrective capacitor', thanks for the link.

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LED spot light dim glow when off

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