Why some LED bulbs glow or flash when turned off

I've noticed that a few LED bulbs continue to glow slightly, flicker or flash even though the power switch is off. This video explains why this happens.

[prashanthb]

I have wasted 1 entire day looking for house wiring mistakes !
My small 1 watt led bulb was glowing even when switched off.
Thanks for this video.

[CJWarlock]

Nicely done, explained well even for laymen. As someone who had to talk to laymen about tech stuff I can recognize a well put explanation with examples. Cheers!

[rich]

Using the same process, you can make an oscillator out of a single transistor, a capacitor and a diode(or LED). Capacitor charges until the voltage is high enough to flow through the LED, discharges, and then repeats. You can even control the oscillation rate with a pot that controls how fast the capacitors charge, and you can tweak the oscillation frequency range by changing the capacitor value. The output is typically a triangle wave.

[MrBurakvatansever]

Thanks a lot John! I have a toaster plugged in a switched socket that is also plugged in a wall outlet. I know it is unorthodox a bit but I wanted to be able to switch the toaster on and off since it has not a built-in switch. I realized that toaster's LED indicator stayed on dimly when I switched the socket off. But when I turned the dial to increase heat (increasing resistance in a way) while the switch was off, the LED went off.

While I was searching for the reasons of this issue, I came across this video and when I heard capacitive coupling, I tried to turn the socket 180° and plugged it in (an European wall outlet) again to tackle this phenomenon. Guess what... It worked :)

I think because of wiring in that socket, the switch was located on the neutral wire. Turning the socket caused the switch to be on the hot wire. Thus, unlike the beginning, LED of the toaster stays off now when the socket's switch is also off.

I am not sure if my approach is the exact solution for my case but hope it helps who has a similar problem. I would like to hear from the experts and broaden my electrical knowledge :)

[curtchase]

You are brilliant! Spot on there! We never had issues like that with old Edison bulbs did we! LOL. Having a wall switch wired wrong is something that would have made no difference with a incandescent lamp. I learned about leakage when I tried using my old skool X-10 switch modules with CFL's several years ago. I'd turn the module off and the tube would still glow and flicker! Learned that the modules had a current bleeder that was used to manually turn on a lamp from it's switch without needing the command from the controller! So, now, if I use a CFL or LED on one of those modules, I have to make an internal mod to kill the bleeder so the bulb won't get the trickle current flow. Kinda tricky. Again, very interesting!

[gandsnut]

"Frank, come look at this... Our neighbor is doing something with a video camera. pointing a wired stick at the power lines." "That's nothing. His wife told me she found him hunched over in a dark laundry room by his dryer, muttering something about capacity couples..." I'm just glad you didn't yammer on about free energy and Tesla.

[jp-umfr]

John my friend, your thumb was VERY close to that 110V. Sort of don't do what I do, do what I say. We don't want to loose you. Where I am it's 245V - OOER! Real tingle time.

[Lilmiket]

wow this is one cool video! i've always wondered why those leds do that. I especially loved the part where it lit up under the power transmission lines! very cool. reminds me of Nikola Tesla lol.

[tqdomains]

Had no idea that an exposed LED can summon the Bifrost. 0:55

[RG-vctr]

Solved my problem. Thanks so much, man!

Installed an outdoor flood light. When I turned it off, there was still some glow to it. Not good. Swapped the white for the black wire in the switch and it works perfectly now. Who knew....? Great explanation here. Thanks.

[Rudolf_Edward]

Hi John! Thank you so much for this video. It now explaines why my IKEA-LED lightbulb was flashing when i hooked it up to my remote-controlled switch WHEN IT WAS SWITCHED OFF. (Here in Amsterdam, it's 230 V 50 Hz, btw). It's a switch that you plug in the socket and then it has a socket by itself and you can dim or switch it by a remote. I really thought that it was a complete switch-off, but appearently it is not the case. Also thank you for the video-bit of 'stealing' current from the high voltage live-wires. As a kid, me and my grandpa were fantasizing about a coil made up of wire and a drum. You showed me it actually works!

[jpridie]

Very interesting video. I have a bathroom fixture with three Philips flat style 60Watt dimmable light bulbs. If I unscrew one bulb out of the three the other two stay on and won’t turn off but they are quite bright still, it’s really weird. I hope the leakage current isn’t costing me on the meter to the house. The outside light fixture on the garage was a 70Watt sodium light with a ballast and I just screwed in a cheap LED bulb to replace the sodium lamp and it works very well.

[MarshallDudley]

What you say is correct, but there is another reason why these bulbs will glow a while after turning off. If the glow dims over several minutes and finally goes out after turning off it is because the white bulbs use a blue LED with a fluorescent coating to convert some of the blue to green and red to get white just like fluorescent bulbs do. This fluorescent coating also has some phosphor properties, where energy is absorbed but not emitted immediately. This energy keeps the phosphor in an excited state for some short time, and as it decays off emits light.

[JisINSANE]

I found 2 problems that cause this. No ground on the circuit causing the neutral to act as a ground which neutrals are technically grounds but a 2nd ground absorbs all the neutral feedback bleed power. And 2 the cheaper led bulb manufacturer making dimmer compatible bulbs never added a bleed circuit resistor around the triac which any little voltage detected can switch  the triac  gate on and cause the bulbs circuit triac  to be permanetley closed and  then glow from the small voltage feedback from the neutral since triacs are used in dimmer compatible bulbs and accept voltage from both directions.

[thezombieguy]

*0:43** Says be more careful to us, but if you notice closely he's accidentally about to touch the line wire.*

[tripjet]

You might wish to include a bridge rectifier for a finer sine stream.

[discerningmind]

Fascinating.  I've wondered why one of the LED units in my home did that.  I don't know much about electrical workings, but in my infantile understanding I figured it was something like this.  I enjoyed the part with the outdoor transmission line.  Thanks!!!

[GaaraMeepo]

This video was informative. I'm going to try re-wiring my switch so that it's on the hot line instead of neutral.

[CommentsAllowed]

9:00 You are a brave man. "Standing here under the 240, 000 watt lines"
Holding a lightning rod in your hand. Thank you for risking your life for science, but we would like more videos, too! ;-)

[JohnAudioTech]

The bleeder resistor can't discharge the capacitor if the resistor is on the AC side of the bridge rectifier. Error on my part.