Light is dimmed when switched off

Question

I have a LED light bulb hanging from the ceiling of the attic room (European electric wiring). This setup used to be all right up until some time ago.

About a week ago I went in the attic and saw that the light although it should have been off it was actually on but dimmed somewhat. So I finished my work there and when leaving the attic I switched off the light. The light was completely turned off. Went downstairs and after some time went back to the attic. To my surprise the light bulb was again on with a dimmed power.

I also noticed that the light sometimes turns off and sometimes just dims down when I turn off the switch.

The attic has 2 lights and one of these, always this one is behaving like this. This specific problematic bulb is connected to a light switch with indicator light (similar to this one ) so when the light bulb is not entirely off (but it should since the switch is off) the indicator light is also not glowing.

Also from what I can remember (not 100% sure of) the switch should control the hot wire (the only in the switch).

Also there are 2 wires the neutral and the phase going to the bulbs. Also I want to mention that outside the house there is another LED bulb (different type/manufacturer) on the same wiring as the attic and kitchen which also is not fully turned off when the switch is off, but this one is always behaving like this, it does not turns off and dims back up later.

I know it's a long description but I wanted to get all the info out there, maybe it helps you guys help me. Thanks in advance for any advice/idea/explanation.

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The switch is not designed to have a nul/neutral connected to it, nor do I have a cable near that switch (although I could install one).

How about if I replace the switch with the indicator with a simple switch (I may already have that someplace) ? Would that help ?

Answer 1

This specific problematic bulb is connected to a light switch with indicator light (similar to this one ) so when the light bulb is not entirely off (but it should since the switch is off) the indicator light is also not glowing.

There's your problem right there.

This indicator is designed to be "on" when the switch is "off", to help you find the switch in the dark. As such, this is a powered switch - similar to motion sensors, dimmers, smart switches etc. The switch needs power to run itself. How do you power a switch?

If power comes to the switch box first, that's a simple matter. But what if power goes to the lamp first, and you have a 2-wire switch loop to the switch? For marketing reasons, you need to cover that case, or half your products will be returned.

With old incandescents, you can leak a small amount of current through the bulb and it won't light up. That is how powered switches solved this. Now they don't need a neutral wire! And so, virtually all dimmers, lighted switches etc. were made without neutral, and relied on this weird trick.

In 2011, North American NEC started requiring neutral at switch loops. As a result, manufacturers are offering powered switches which use neutral and don't leak current through the bulb.

So the switch hasn't been shutting off power at all. It's been leaking some through.

This is "hit-and-miss" with LEDs. LEDs are really good at converting all current into light. Therefore that leakage current causes the LED to glow dimly. (mind you light is perceived on a decibel curve, so 100 times the light doesn't seem 100 times brighter, only 20dB brighter).

And in your case, the leakage current which the LED will permit is not bright enough to light the switch's light.

The simplest answer is change to "dimmable" LEDs, which are designed to expect small leakage current through them. You can also fit a listed bypass capacitor such as Lutron's LUT-MLC.

However the ideal solution is wire in neutral and then use a lighted switch designed to use neutral.