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We have a Lutron Caseta dimmer switch which controls a set of four downlights.

I tried replacing the bulbs with Hue downlights (knowing full well that these wouldn't play well with the dimmer, except perhaps at maximum brightness), and observed the following behaviour:

  • None of the lights would receive power when all four downlights were smart bulbs.
  • The lights would all receive power if three downlights were smart bulbs, and one downlight was the original regular downlight. However, in this state:
    • The smart bulbs pair and operate properly, except that:
    • If the smart bulb's app-based dimmer was set to below 50% brightness, then all the bulbs, including the regular bulb, would turn off completely instead, then all four bulbs would turn back on again about two seconds later.

What could be causing the app-based dimmer to cause the entire circuit of lights, including the regular bulb, to briefly turn off then on again?

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You're looking at the problem upside down. You are thinking the smart bulbs are causing it. Actually, the Lutron Caseta dimmer is causing it.

The smart bulbs are behaving normally, however their normal behavior is breaking the dimmer.

The dimmer can't deal with four smart bulbs downline of it because (very typically) the dimmer doesn't have a neutral and needs to pass current through the bulbs at all times. The Hue bulbs aren't cooperating with that, that's why it needs one plain bulb still present. This is stock advice we give around here when someone tries to put n LED bulbs on a dimmer (try changing 1 back to incandescent; success = incompatible dimmer).

When you set the smart bulbs below 50% brightness, again there is now too little current going through them for the Caseta dimmer to function.

You knew this wasn't going to work. Convert the Caseta to a plain switch and don't look back.

Hey, free dimmer! :)

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  • I am shocked (pun not intended) that code hasn't baned those types of smart switches by now. I've seen new lutron motion switches as recently as last year that didn't work unless ground was connected. And their entire casing was plastic. May as well have been double insulated. They were definitely using that ground as a neutral for whatever mili-amp it needs to run a photocell and 555 timer.
    – Billy left SE for Codidact
    Commented Jul 5, 2021 at 23:02
  • @BillyC. they actually got a concession to allow them. UL requires they be built to be bulletproof in terms of inability to leak a dangerous current onto the ground wire. And NEC calls out a maximum of 10(?) smart switches per circuit, so the UL-allowed bypass current isn't enough to trip GFCIs. They got it all figured out!
    – Harper - Reinstate Monica
    Commented Jul 5, 2021 at 23:14

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