New LED bulbs pulsing when off!!! - Page 1
Forum section: electronics / general

author: metrologist
author_rank: Super Contributor
timestamp: November 25, 2017, 12:41:16 am
content: I just bought replacement screw in LED bulbs and noticed there was a slight light pulsing when the switch is off!!! The switch is a wall dimable switch and I did buy dimable bulbs...The other fixtures in this house are 4-prong CFL and I'm about ready to go candle lighting...

author: BradC
author_rank: Super Contributor
timestamp: November 25, 2017, 01:59:42 am
content: Induced emf in the active charges up the bulk storage cap until it tries to start, discharges the cap and the process repeats.

author: hermit
author_rank: Frequent Contributor
timestamp: November 25, 2017, 02:20:23 am
content: Just a shot in the dark here and maybe completely irrelevant but the LED's I've looked at all say they need some kind of specific dimmer. Is your wall unit for an old incandescent fixture? I've wondered about the dimmers but haven't been close enough to buying the LED's yet to check it out more closely.

author: TerraHertz
author_rank: Super Contributor
timestamp: November 25, 2017, 02:52:27 am
content: Old style dimmers usually have an RC snubber network in parallel with the triac, to protect the triac from fast mains spikes.Unfortunately that RC network passes enough energy to the active line, to charge up the mains rectifier circuit/cap in the LED bulb, to where it will try to start.

author: BradC
author_rank: Super Contributor
timestamp: November 25, 2017, 02:55:02 am
content: Quote from: TerraHertz on November 25, 2017, 02:52:27 amNot to say they don't exist, but I've never seen a dimmer that is used as a switch by dropping the duty cycle to 0. All the dimmers I've ever seen have been coupled with a mechanical switch to break the active pre-dimmer.

author: georges80
author_rank: Frequent Contributor
timestamp: November 25, 2017, 04:19:04 am
content: Actually most triac dimmers just stop firing the triac to 'turn off' the bulb. So, if they have a snubber which has a low enough impedance then enough current will flow 'around' the triac to charge the LED ballast (as already mentioned by TerraHertz) and this will keep the LED unit barely lit or it can strobe/flicker.In my current job, I've seen/measured this in actual products. So, indeed, this is likely the problem with your dimmer (get a more modern one that is compatible with dimmable LED bulbs).cheers,george.

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2017, 04:26:06 am
content: Quote from: BradC on November 25, 2017, 02:55:02 amQuote from: georges80 on November 25, 2017, 04:19:04 amMost of the light switches in my house are dimmer switches and all of them have a mechanical off position that isolates the bulb circuit.Quote from: metrologist on November 25, 2017, 12:41:16 amIf your wall switch does not have a mechanical off position (a solid click) then you might replace the switch with one that does?It is possible even then that the bulbs might flicker. LED bulbs are very sensitive and induced voltage in the wiring might cause visible flicker in dark rooms.

author: Halcyon
author_rank: Unknown
timestamp: November 25, 2017, 04:26:29 am
content: Good example of what can happen with some switches/dimmers:Skip to about 8:10 if you can't be bothered watching it all.

author: georges80
author_rank: Frequent Contributor
timestamp: November 25, 2017, 04:47:25 am
content: Quote from: IanB on November 25, 2017, 04:26:06 amThe mechanical switch is to change the bulbs - i.e. it mechanically disconnects the power path. Many don't have that mechanical switch. It is a little lever/clip/etc separate from the main dimming/control functionality.Most modern dimmers use the triac to turn off power to the load. I've opened enough of them to know how they functionThe flicker at 'off' is more than likely due to the snubber that was designed prior to LED bulbs becoming common.cheers,george.

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2017, 04:53:43 am
content: Quote from: georges80 on November 25, 2017, 04:47:25 amI'm sorry, but every phase angle dimmer I have ever encountered or owned has had a mechanical disconnect off switch that completely isolates the current path. (I'm talking about ones with a mechanical movement, not touch sensitive dimmers.)Therefore there is no way to say whether the OP has a switch with or without a mechanical disconnect. You cannot assert what you do not know, you can only speculate.

author: georges80
author_rank: Frequent Contributor
timestamp: November 25, 2017, 05:07:33 am
content: ^ Well, you have had old ones. Modern ones do NOT have a switch. Modern wifi/bt etc dimmers do NOT have a switch - regardless of touch operation or mechanical button/slider etc. I have a little experience with modern dimmer design.Even non-'smart' dimmer units (newer lutron, leviton, ge etc etc) use their Triac to turn off the load - NO mechanical switch in the 'off/zero' position of the dimmer.I'll speculate that the OP's problem is the snubber causing the LED to flicker (older dimmer design). I have seen older products that have that issue due to the extremely low energy required to charge the ballast to a point it triggers.cheers,george.

author: Falcon69
author_rank: Super Contributor
timestamp: November 25, 2017, 06:59:24 am
content: to the OPThis is so funny that you say they are pulsing, and seems those are house bulbs.I just bought some LED bulbs for my truck. When I turn the lights off, they pulse and flicker as well. It's weird sometimes. Almost like the strobing of police lights. I wonder if it has something to do with the automatic light function of the truck (turns on when it starts getting dusk outside).I even tried manually turning them on and then turning off when I turn the key to the off position. They still flicker.

author: Rerouter
author_rank: Super Contributor
timestamp: November 25, 2017, 07:40:21 am
content: Falcon, same deal there, some european standard trucks run a light check process, where they keep on checking to make sure a bulb has not blown, they commonly do this by running them at less than 1% duty on the assumption that this would be too low to normally see,Older trucks uses drivers that needed a small load to truly remain off, without a resistive bulb they will build up enough charge,for a few makes i have seen, a 10K resistor in parrellel with the 12/24V led bulbs was enough to stop the older style flashing, but not the newer style bulb check.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 25, 2017, 09:10:04 am
content: Replace one LED on the dimmed circuit/branch with an incandescent lamp. Problem solved.Tim

author: Kleinstein
author_rank: Super Contributor
timestamp: November 25, 2017, 09:50:27 am
content: Some LED lamps can flicker even with very low capacitive coupling. I have this with one light controlled by 3 old style mechanical switches - thus no dimmer or snubber, but quite some length of cables (maybe close to 20 m) and likely this cable capacitance is enough. In my case, I don't mind the flashing - it more like a feature and not a bug.Different LED lamps use different internal circuits. So chances are a different type of LED lamp can stop the flashing.

author: metrologist
author_rank: Super Contributor
timestamp: November 25, 2017, 12:28:09 pm
content: I had two thoughts:If it does not damage the lights, then I don't care, aside from whatever wasted power. They are not really pulsing much and are just very dimly lit. It is hard to see during the day.It might be that the circuit is mis-wired, perhaps to a parallel neutral. It is in a 3-way circuit (or two switches), and one of the panels has a total of 6 switches. So I could see the worker getting confused.The switch is a flat rocker with a small slider on the side, and is a Luton switch installed about 7 years ago. Another room uses the same switch and I installed LED bulbs, and they do not pulse. A different brand bulb, not dimmable so I blocked the dimmer.One more detail is that this actual switch is illuminated when off. I opened it up and this is the switch, D-600P:http://www.lutron.com/TechnicalDocumentLibrary/0301689.pdfI installed one of the old inc. bulbs and it stopped pulsing. I might just go get a replacement switch without a dimmer. Dimming is lame anyway.So I install LED's to save money and immediately spend all that savings on new switches.

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2017, 01:08:29 pm
content: Quote from: metrologist on November 25, 2017, 12:28:09 pmThat's a really important detail!The way illuminated switches work is they draw current through the bulb in order to drive the illumination (e.g. neon lamp). So if the bulb is really sensitive it might flicker from the switch illumination current.

author: Vtile
author_rank: Super Contributor
timestamp: November 25, 2017, 05:24:54 pm
content: Quote from: IanB on November 25, 2017, 01:08:29 pmHmm......And forementioned capacitive coupling I tried a few months ago ask around about it, but no hit. I were particularly interested if someone knows anything at all if the standards do take these account with the led lights / bulbs. None didn't know and I didn't find anything on real on the subject searching the internet back then. I see that troublesome as many older houses do have really bad capacitive coupling going on in their wires.

author: kripton2035
author_rank: Super Contributor
timestamp: November 25, 2017, 05:43:20 pm
content: my leds didn't bulb, but they where very little on even when the switch is off... happens only with a two-way switch in the house.I had to install a small capacitor (100nF 400V) in parallel with one led in the circuit, and everything went really off.

author: Seekonk
author_rank: Super Contributor
timestamp: November 25, 2017, 06:15:36 pm
content: I use standard 120V 10W LED as a night light for my dog. I just put a 0.1uF capacitor in series. This is actually pretty nice for a porch light. Just put the cap across the switch and you have enough light to find it to the porch and get the right key and it runs for about nothing in cost. Some <$2 bulbs dim, flash as stated and some don't turn on at all. I always used .1uf RC networks from the company I worked for since they were free on the load to solve leakage problems.

author: Falcon69
author_rank: Super Contributor
timestamp: November 25, 2017, 07:52:47 pm
content: I just got a reply back from Kensun on my issue of the LED headlight bulbs pulsing and strobing when turned off. They were very nice and quick to send them out. Hopefully it works. If it works, I'll probably by a couple sets (Fog, High Beam, and Low Beam) for the car from them. That was good customer service from them.They didn't even ask for a picture of what it is doing or even argue with me about the install or anything.They are sending me some resistors (i suspect they are the same kind, aluminum wound, that I put on my flashback LED's turn signals to stop them from rapid flashing) to put on the bulbs. They did say they get hot.So it sounds like it is a discharge issue of an internal capacitor.I've also read that some computer systems on cars send small voltage signals at low current to the LED's to check to see if they are still on, and that could cause the flashing/strobing/pulsing when turned off. But that's in newer cars. Mine is 10 years old now.As far as inside house bulbs doing that, I've never noticed it before. I have noticed bulbs only lasting a year or so, when they are suppose to last like 12 years.Before they die, they are random as far as turning on when you hit the light switch. Sometimes they don't work at all, sometimes they do. This goes on for a few weeks before they completely die. Maybe it's the brand, cheap Home Depot ones.