LED bulbs flashing

[SandyLyon]

My daughter has a 4 lamp light fitting in her kitchen, the bulbs are all Phillips 4.5W, 2700K, GU10, it is wired with a 2 way switch by the back door and a 2 way switch by the dining room.

This set up has worked satisfactory for approximately 6 years, last night when she was about to go to bed, she turned off the lights and they started flashing rapidly (say twice a second), turn them back on all good, turn them off and rapid flashing again.

She has had no electrical work done, nothing has changed, any ideas as to why this has suddenly happened and how to fix it.

Thanks in advance.

Sandy.

 

[SandyLyon]

I’ve just changed one of the bulbs for a Halogen one and it now operates correctly.

Puzzled as to why it’s worked ok for so long then suddenly this ?

 

[FrodoOne]

If both switches involved are "mechanical" and not "electronic" in any way I can see no reason why the Off condition of these lamps would not be a complete open circuit.

"Flashing" (how brightly ?) at 500 mS intervals indicates leakage - of some sort.
The fact that installing one Halogen lamp in the set "cures" the problem virtually proves that there is leakage somewhere.

Does the problem exist in both "Off" combinations of the two-way switching?

 

[bernardgreen]

I can see no reason why the Off condition of these lamps would not be a complete open circuit.

The circuits never a complete open circuit, there is capacitive coupling between the conductors in the cable(s) to the switch(es). This capacitive coupling is in parallel with the open switch(es) and as such provides a path for a small amount of current ( energy ) to reach the driver in the lamp.

The driver in the LED lamp will accumulate this energy until it is enough to cause the LED element to light up. That depletes the store and the LED goes dark until the driver has enough energy to create another flash of light,

 

[SandyLyon]

If both switches involved are "mechanical" and not "electronic" in any way I can see no reason why the Off condition of these lamps would not be a complete open circuit.

Both switches are Single Gang 2 way standard mechanical type, not dimmer switches.

"Flashing" (how brightly ?) at 500 mS intervals indicates leakage - of some sort.
The fact that installing one Halogen lamp in the set "cures" the problem virtually proves that there is leakage somewhere.


Probably about 50% brightness, rapid strobing at first, a couple of times a second, then after a while once a second.

Does the problem exist in both "Off" combinations of the two-way switching?


Yes,

I’ve done a bit of research on the net and it appears to be an all too common problem with LED bulbs, what puzzles me is to why it’s suddenly started doing it after years and years of normal use.
There has been absolutely no electrical work in recent months.

 

[SandyLyon]

The circuits never a complete open circuit, there is capacitive coupling between the conductors in the cable(s) to the switch(es). This capacitive coupling is in parallel with the open switch(es) and as such provides a path for a small amount of current ( energy ) to reach the driver in the lamp.

The driver in the LED lamp will accumulate this energy until it is enough to cause the LED element to light up. That depletes the store and the LED goes dark until the driver has enough energy to create another flash of light,

Thanks Bernard, as above reply, having done some research it appears to be a well know problem with LED bulbs, but this issue has only just occurred following approximately 6 years of trouble free use ?.
I don’t recall her even changing a bulb during that time, certainly no electrical work carried out on the lighting circuits.

 

[ericmark]

The use of a load capacitor will stop it, likely there was a load capacitor or resistor built into the bulb, and this has failed, electrolyte capacitors have a limited life, and do fail, it is as @bernardgreen has said due to using the British system of taking power from light fitting to light fitting and then switch wires from fitting down to the switch, had they been wired power to switch and then to fitting the inductance and capacitive linking would cancel each other out, this is why we use coax cable to TV aerial, but until the compact fluorescent and LED lamp at 50 Hz we could get away with treating it like DC.

The reaction of LED lamps and electronic neutral less switches has been a problem for a long time, be it a wifi switch, or dimmer switch, in the main simple on/off switching is not a problem, however with two way switching the length of cable is much longer so the problem is common with two way switching.

Often swapping one bulb will fix it, it does seem odd, specially with the shimmer when switched on that swapping one bulb with stop others from the shimmer, but it does, and does not need to be a tungsten bulb as the odd one out.

The bulbs I had problems with were G9 the small bulb would flash (when off) and shimmer (when on) there was a glass tube which screwed over the bulb, swapping one bulb for a quartz or for the larger bulb would stop both, but clearly the cover would not fit with larger bulb, so had to change all 5.

 

[bernardgreen]

Alternative is this device

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 )
RS Stock No.: 206-7869
Mfr. Part No.: PMR209ME6470M100R30
Brand: KEMET

There are other sources

 

[Harry Bloomfield]

If both switches involved are "mechanical" and not "electronic" in any way I can see no reason why the Off condition of these lamps would not be a complete open circuit.

"Flashing" (how brightly ?) at 500 mS intervals indicates leakage - of some sort.
The fact that installing one Halogen lamp in the set "cures" the problem virtually proves that there is leakage somewhere.

Does the problem exist in both "Off" combinations of the two-way switching?

The flashing is a common problem and is due to capacitive coupling between the live and switch wires. That is enough to allow some leakage of current to the LED's, which then causes them to build up enough voltage to enable them to flash occasionally. Simply adding a normal incandescent lamp will discharge the voltage and prevent the flashing, or you can buy a small resistor to connect between switch wire and neutral to fix it. Another way, as it is not detrimental is to simply ignore it.

 

[bernardgreen]

It is strange that it is now happening after 6 years of problem free operation.

Possibly a slight increase in dampness ( condensation in the kitchen ) has increased the leakage from Live to Switched Live in one ( or both ) switches and/or in the lamp fitting,

 

[bernardgreen]

small resistor to connect between switch wire and neutral to fix it.

NO..... not a resistor. it is a capacitor that s needed. Preferably a capacitor with a series resistor to act as a fuse in case the capacitor fails and becomes a short circuit across the mains.

 

[SandyLyon]

Thanks for your replies guy’s, it’s not practical to re-run the cables to the fitting so will look at putting a capacitor across the light fitting

 

[Harry Bloomfield]

Thanks for your replies guy’s, it’s not practical to re-run the cables to the fitting so will look at putting a capacitor across the light fitting

You will need to research the correct part to fit. It fits at the ceiling rose connection.