I have a set of 2 recessed bulbs controlled by the same switch. After one of them burned out (it was an incandescent bulb), I replaced it with an LED bulb, which worked fine. Right after, I replaced the other incandescent bulb in the set with another LED from the same box, and now both bulbs are significantly less bright than the first LED was on its own when it was paired with the incandescent bulb. The first LED is also less bright when there is no bulb in the second socket, and in both cases the LED bulbs take longer to turn on than the LED plus incandescent set did. What could be causing this, and will I need an electrician to address it?

The are connected to a dimmer switch, and the replacement bulbs are both 65W equivalent dimmable LED bulbs.

  • 5
    But does the dimmer like LEDs? Older dimmers of incandescent age sometimes work differently, that LEDs do not like.
    – crip659
    Commented Sep 30, 2023 at 22:58
  • Maybe while you’re pulling out the dimmer to check its specs, you can check for loose connections and any adjustment pots/sliders on the dimmer. Commented Sep 30, 2023 at 23:04
  • Put a tungsten bulb in, it should brighten it back to where it was. If so you have the wrong dimmer.
    – Gil
    Commented Sep 30, 2023 at 23:41
  • 4
    Try a plain switch rather than the dimmer and see if the weirdness goes away. The reality of LED-compatible Dimmers and Dimmable LEDs working together is uglier than you might expect.
    – Ecnerwal
    Commented Oct 1, 2023 at 1:44
  • Try different/better dimmable LED bulbs, many newer models work fine with old dimmers that give lesser bulbs issues.
    – dandavis
    Commented Oct 1, 2023 at 23:30

1 Answer 1


It's the 'switch'

It's a timer, dimmer, motion sensor, smart switch, lighted switch, or other sort of dingus which requires electricity to power its own internal functions.

Normally when you want to power a thing, you grab always-hot and neutral, typically black and white at most receptacles. However, there is a thing called a switch loop which provides only always-hot and switched-hot to a switch; not neutral.

To cope with switch loops, the heritage way to power a "powered switch" was to leak a small amount of current through the incandescent bulb. Which by nature don't mind that. The current is too little to make them flicker or glow.

However now in the LED age, that does not work.

Our classic litmus test for this, in multi-bulb fixtures, is to use all LEDs except make 1 bulb a real incandescent. if the problem vanishes when you do that, then the above is the cause. Of course, you've already done this test in reverse, and got a positive (in the medical sense) result.

So cure #1 is come up with a path for the leakage current. Either use LEDs designed for this, typically marked as "dimmable", or add a LUT-MLC capacitor module which will do the same thing. Cure #2 is to modernize the "switch" or just get rid of it.

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