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Wazzup with these new fangled LED's?
Posted by: Buzz
Date: March 19, 2017 03:23PM
Replaced the old school non-LED rated dimmers with (then) new LED rated dimmers a bit over a couple of years ago. A hanging ceiling light w/ 100W equiv LED had been working fine until a few weeks ago. It recently decided it doesn't like being set in low mode, and has started to sometimes flicker indiscriminately. Actually, perhaps a more accurate verbal description would be erratic slow-ish pulsations punctuated by intermittent series of 2 - 4 popping bright flashes. Sometimes just ramping the light back up and then re-dimming it solves the problem. Sometimes that doesn't work, so I either turn it off, or set it up to medium.

Bulb works fine in tests w/ floor lamp, but that lamp has a different/built-in dimmer, and is a base down vs. the base up position of the hanging fixture. The hanging fixture is open and well vented, though the bulb is rated for enclosed ceiling fixtures so I don't think heat is an issue. When it does get warm in the room, the fixture is close to the window, and is also above the oscillating fan on the dresser underneath it which bathes it in flowing air as it goes thru its paces.

Bulb? Dimmer? Combo thereof? Fluctuations in the building's power that I can't otherwise tell? Late 1960's building w/ original wiring that is way under current code. Any other easy/convenient tests to do to help figure it out? ...It was a $20 (+tax) bulb that was supposed to outlast me.
Thanks.
==
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Re: Wazzup with these new fangled LED's?
Posted by: Onamuji
Date: March 19, 2017 03:55PM
Most LEDs do not dim like incandescent bulbs do.

They are either wholly on or wholly off.

So, the dimming effect is actually a strobe that's too fast for most people to detect.

If you're detecting the strobe effect then the most likely scenarios are either it's not getting clean current and that's interrupting it during a critical part of the cycle, or else the chip that's governing it is flaking out.

But another option just occurred to me. Your spinning fan may be casting a shadow or reflecting light back and making the strobe effect detectable. I don't think that this is the case because of the "popping" you've described, but it might be worth playing with the fan for a couple of minutes to see whether it makes a difference.



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Re: Wazzup with these new fangled LED's?
Posted by: billb
Date: March 19, 2017 04:00PM
loose connection in a vibrating light ?
fan off still flickers ?



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Edited 1 time(s). Last edit at 03/19/2017 04:01PM by billb.
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Re: Wazzup with these new fangled LED's?
Posted by: Carnos Jax
Date: March 19, 2017 04:41PM
Quote
Onamuji
So, the dimming effect is actually a strobe that's too fast for most people to detect.

Fascinating, I did not know this.
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Re: Wazzup with these new fangled LED's?
Posted by: TheCaber
Date: March 19, 2017 05:13PM
Pulse-width modulation



=TC
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Re: Wazzup with these new fangled LED's?
Posted by: Buzz
Date: March 19, 2017 08:21PM
Cabe- I think that mighta made sense to me about fifty years ago... now, not so much. :-)

Doc/Bill- fan does not seem to have any effect on light symptoms*, and fan is only on when it gets too warm in the room. The pulsating is a rather slow ebb and flow of dimming and brightening within a few percent range; the popping is quite bright, not sure how close it is to full brightness, but the pops are quite bright. *There is sometimes a slightly noticeable strobe effect associated w/ the pulsing, but I haven't paid close enough attention to tie it to the fan, though FWIW, the 120Hz HDTV is pretty much always on in conjunction w/ the subject light, and Cabe's link had something in there about dimmers operating at that frequency. The fan has been on less than a third of the time.

Still doesn't explain everything, but I can see (pun accidental) how the competing frequencies might accentuate the perception of the symptoms. So, still looking for a test/fix... is it the chip in the light? or the dimmer? or flaky current from ancient wiring? or some combo of two or more? There have been wiring related issues over the years around here, so all desktop computers always go on high grade UPS's. Again, it's an intermittent issue, as sometimes when dimmed the light is OK. When it happens, it's either instantaneous, or within a few seconds of dimming; if it doesn't happen within about fifteen seconds, it seems good for the long term, though a couple of times it acted up after an hour and a half or two of being dimmed... so not sure if it would always eventually happen now, as we're only talking about heading into bedtime and turning the light off.
Thanks.
==
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