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My wife was straightening her hair today when she noticed that whenever the straightener element turns on, the LED lights in the bathroom flicker. The lights are on the same circuit as the outlet (which is GFCI), there are no dimmer switches installed anywhere in the house, the house was just built, and every single light in the house is LED. On this circuit, there are only the 4 LED bulbs, a recessed led light, the bathroom outlets, and the smoke detectors.

I've noticed flickering before, but have been unable to isolate the cause. I tried putting the straightener on a UPS with filtering, to see if it was some kind of noise being generated, and it did not help.

The flickering is visible on the 4 Feit Electric "Edison style" dimmable LEDs, as well as the (unknown branded) recessed light.

  • “Feit” is the problem. One product of Costco’s that is below standard. – Tyson Jun 1 '18 at 0:37
  • Buy GE, Phillip or Sylvania bulbs and I bet the problem goes away. – Tyson Jun 1 '18 at 0:47
  • Four failing at the same time would be surprising even for Feit. (also beware Utilitech and Lights of "America") A surprising good one: Ikea. However I suspect another cost-cutting trick: the backstab. 1500W loads tend to "bring out" backstab failures, another one popped up an hour later. – Harper Jun 1 '18 at 1:19
  • @Harper flat irons aren’t as greedy as you think.. probably 80-170 watts is typical. – Tyson Jun 1 '18 at 2:29
  • Well, that's even more alarming! If the wiring was healthy, the Feits shouldn't even know it's in use. – Harper Jun 1 '18 at 2:32
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this happens when LED bulbs don't have proper (or any) DC conditioning. Cheaper decorative LEDs in the US use a simple circuit of ~50 LEDs in series, with no other regulation. This also means they are off half the time (60 times a second they blink), but some bulbs will have multiple series strands in reverse polarity, so that at least one "filament" is lit the majority of the time and the flicker rate is doubled to a less-noticeable 120Hz.

These styles of bulb are extremely simple electrically, literally about the same as a tungsten bulb. They are nice and pretty and cheap to produce, but they doesn't work very well. Small fluctuations in voltage will have large effects on the light output because the LEDs are unregulated and being driven close to their limit. Unlike tungsten, which has a linear voltage-to-lumen ratio, LEDs produce exponentially more light with voltage above their specification. So while a 2v dip on tungsten might decrease light ~2%, it can cut the LED's ouput by ten times that or more.

You want a more expensive bulb that will properly convert the incoming AC to lower-voltage DC to keep the output steady over a wide variety of input voltages. If there's a short delay from when you turn them on to when they output light chances are they won't flicker no matter what you do.

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