I just bought a house with LED lights in the dimmable ceiling fan that never shut off. I thought the fan was defective. But I put new dimmable LED bulbs in, and everything worked fine. I found that with even one new bulb in the socket, all of the bulbs turned off correctly. So I presume that the old bulbs were defective, but I'm curious about what's going on, and wondering if it's safe. It seems like if the switch was actually off there shouldn't be current, and the bulbs would be off. And if the defective bulbs can glow on that circuit, then there must be energy being wasted even though the "good" bulbs appear to be off.
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\$\begingroup\$ Does this answer your question? LED lamps keep glowing when dimmer is turned off \$\endgroup\$– winnyCommented Mar 9, 2022 at 8:23
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2 Answers
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Bulbs are not defective, they are just cheap as they don't have a mechanism to prevent lighting up with capacitive leakage current.
A lamp that does prevent lighting up will add enough load to prevent all the other lamps from lighting up as well.
The phenomenon is safe. When the switch is off, there is long unpowered wire next to long powered wire and two conductors with insulation in between is a capacitor, so it is capacitive leakage.
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LEDs start to slightly glow at extremely low currents in the microamps range. And wire leads from and to the switch are often parallel which leads to slight capacitive coupling. Also, switches have some capacitive coupling, that's just physics and nothing to worry about.
Now old incandescent light bulbs have a loe resistance when they are cold. So they just conduct that small current away without anyone noticing.
LEDs are completely different in that and it can happen that they will always slightly glow. Newer LED bulbs have changed the electronics, so they don't show that behaviour.
Does it mean, that there is something dangerous going on? No, it does not necessarily mean, that there is something wrong or even dangerous going on. It's even probably, that noting is wrong!
Does this mean, that there is nothing wrong than? No, it does not mean that everything is alright! It COULD be a symptom of someting being wrong with your wiring but it is not necessarily the case.
This Article explains some possible reasons and how to mitigate them.
