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Light fixture uses dimmable LEDs and a dimmer switch, but flickers -- how can I fix this? Question
My dining room includes a chandelier ceiling fixture with five sockets, controlled by a dimmer switch on the wall. I've lived here for 20 years and this was already in place when I moved in; I don't know any more history. There is no documentation, but I was verbally told that it was rated for no more than 60 watts per socket. (This was in the days of incandescent bulbs.)
I would like to be able to have brighter overhead light available -- it's fine for eating and entertaining, but sometimes we play board games on that table and want more light. Since LEDs consume only a small fraction of the power that the original incandescent bulbs did, I reasoned that I could use brighter LEDs so long as they are marked as dimmable.
I replaced the bulbs with dimmable 8W ("100 watt equivalent") LEDs, and I now get intermittent flicker, sometimes mild and sometimes extreme. It doesn't come from only one socket, though it doesn't always come from all of them at the same time.
How do I debug and correct this? Is my problem likely to be with the bulbs, the dimmer switch, the whole fixture, or the wiring? I'm not an electrician; what (if anything) can I investigate on my own before hiring one if it turns out I need to replace something?
1 answer
The following users marked this post as Works for me:
| User | Comment | Date |
|---|---|---|
| Monica Cellio | (no comment) | Sep 7, 2023 at 20:55 |
The first thing I would try is to replace the dimmer. New dimmers work differently than old dimmers, at least the right kind of new dimmer.
Old dimmers worked by turning on their output for part of each power line cycle. A power line cycle is a sine wave, and these dimmers kept the output at 0 at the start of the sine cycle, then jumped to the full output later in the cycle. The amount later controlled the dimness of the output.
This worked for ye olde fashioned LEBs (light emitting bulbs) because they just by heated up from the applied power. More power meant higher temperature, which generated more light. That's also why dimming such bulbs made the light more orange. Lower temperature not only results in less emission, but that emission is shifted toward the red end of the spectrum.
LEBs took multiple cycles to meaningfully change temperature, so chopping up individual cycles didn't matter. The resulting average1 is what mattered.
One drawback to such dimmers was that they caused nasty radio interference. Any sudden jump, like when switching from 0 to where the power line cycle happened to currently be, radiates lots of radio noise that the FCC and other regulatory agencies increasingly prohibit.
Another problem is that LEDs don't work on heat at all, and can't just be connected to the power line directly like the old LEBs could. LED bulbs actually have an electronic power supply inside that convert line power to something very different that the LEDs use internally.
The power line sine looks like a wildly varying voltage to the LED power supplies. They are designed to handle that, so that's OK. However, they are at least partially designed to smooth out the power to the LEDs, even though it comes in as two lumps (positive and negative) per power line cycle. In effect, the power supply tries to keep the power to the LEDs somewhat constant despite the wildly varying input power. Note that this largely defeats what old dimmers do.
The power supply in dimmable LED bulbs still needs to smooth out the power to the LEDs because light flicker at the power line frequency is quite annoying. However, they track the rough average input power and adjust the level of the smoothed out LED power accordingly. The LED brightness then fluctuates with the level of input power.
The old style dimmers that cut off parts of the power line cycle and cause large sudden jumps make it more difficult to create the smoothed out power to run the LEDs internally in the bulb. It can also confuse the circuitry about the average input power that it's supposed to adjust the LEDs brightness to.
Another issue with old dimmers is that they expect the load being dimmed to draw power at any voltage. The LED power supplies might not do that, so an old dimmer can sortof flicker and sputter on and off. This is probably the effect you are seeing. Note that your LED bulbs already draw way less power than the original LEBs, even when fully on. It's quite possible they just don't draw enough current for the old dimmer to work, especially when dimmed.
New dimmers work on a different principle that causes less radio interference and is more friendly to the power supply in LED bulbs.
Since you already have the LED bulbs you like, go back to the same store and ask for a dimmer that works specifically with those lights. You should be able to replace the old dimmer with a new one. This is a do-it-yourself project if you're comfortable with things like replacing light switches and power outlets. Otherwise, hire an electrician to do it. It shouldn't take long, well under an hour. Since they often bill in hour increments, maybe you can find a few other projects for them to do while they're already out there.
1 Actually the RMS (root mean square), which is different from the average, but that's a nit that would only be a distraction to this level of question. I'm putting this here only to head off the otherwise inevitable outrage from some users about how it's RMS and not average, blah, blah blah.
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