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coming to the experts because I can't figure out what's going on and why.

Goal Install a smart 3-way dimmer switch that allows 8 recessed LED lights to turn on/off and dim correctly.

Background

  • In my living room, I have 8 recessed LED lights that were previously on a Lutron dimmer light switch that worked perfectly and dimmed the lights correctly.
  • I replaced the Lutron dimmer switch with a TP-Link smart 3 way dimmer switch and all 8 recessed LED lights turn on from both switches.
  • The lights are Sylvania RT6 and are currently installed using a retrofit adapter that screws in to the light socket in the can, and has a cord coming out of it with a plug that attaches to the plug on the light itself.

ISSUE: Though the lights do turn on with the smart 3-way dimmer switch, the lights do not dim anymore.

Troubleshooting Steps

  • Validated the smart switch wiring and confirmed it was correct on both the main and satelite switch
  • Added the Lutron switch back to confirmed it was able to dim the lights correctly using the same wiring.
  • Reinstalled the smart 3-way dimmer switch
  • Called an electrician and had them confirm the wiring was correct, even though they didn't know what would be preventing the dimmer from working as they weren't as familiar with smart switches.
  • Bought a few different varieties of similar LED recessed lighting, installed in one of the 8 recessed lighting spots, and found they all turned on, but the dimming did not work.

Interesting Findings

  • Today, with the smart switch installed, I removed one of the recessed lights completely, and just screwed in a dimmable LED bulb directly into the light socket, and that bulb turned on AND was dimming as expected with the smart switch reinstalled.
  • In addition to that new bulb working and dimming as expected, all of the other recessed LED lights now began to dim as well.
  • I took the LED bulb out and the other recessed LED lights would turn on, but would no longer dim.

Please Help! There must be a reason that installing this LED bulb allows all other LED recessed lights to turn on and dim as expected, but I can't figure out why.

I'm wondering if I should try removing the retrofit adapter and just splice the cables from the LED recessed light directly to the power cables. However, since I know that all of the other recessed lights are installed the exact same way with the adapter, and I've seen that they can be dimmed with this smart switch, I don't think that answers the question.

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Update 1 Thank you all for the comments so far. I did test removing the adapter from the equation and connecting the pre-existing Sylvania LED light directly to the hot and neutral. The light turns on correctly but it and the other lights still do not dim. This confirms the adapter is not the issue.

Update 2 The new bulb I added that allowed dimming on all 8 lights seems to be pretty standard. It’s a GE LED, 800 Lumens, 2700k, 10w, 104mA, 120VAC, 60Hz. Model: LED10DA19/827.

Update 3 For anyone who may have a "try this", please let me know. I'm willing to try just about anything, but hoping to avoid having to replace all 8 recessed lights.

Update 4 When thinking about this more, I realized that the answer lies somewhere in the former Lutron 3-way dimmer switch that was previously installed. Since this switch allowed the lights to dim before, it means that there is something in this switch that allowed the lights to dim. Whatever "it" is, my smart switch doesn't have it.

The only difference that stands out is that the old switch did not require a neutral, while the smart switch does. Does that shed any light? (pun intended)

Here is the link to the Lutron switch that was on there before: https://www.lowes.com/pd/Lutron-Skylark-Single-Pole-3-Way-White-LED-Slide-Light-Dimmer/4165017

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    The short answer is that LED and dimmer circuitry varies, and you have stumbled upon an incompatibility which the LED bulb substitution rectifies.
    – isherwood
    Commented Nov 1, 2022 at 16:20
  • The retrofit adapter is not the issue. I checked and the RT6 is a 120V bulb, so the retrofit adapter is purely "mechanical" - i.e., it makes everything fit right and connect properly but it isn't a transformer or rectifier or driver circuit, etc. Actually, if it was any of those then splicing the cables directly would release the magic smoke. Commented Nov 1, 2022 at 16:36
  • What is odd is that dimming works with one alternate bulb, but that is similar to (though likely a different technical reason) circuits that leak current through hot when "off" for operational purposes (timers, motion sensors, etc.) that won't work (or cause flashing) with all LED but work OK with one incandescent and the rest LED. Commented Nov 1, 2022 at 16:36
  • As updated in the description, I can confirm the adapter is not the issue as I have the light connected directly to the hot and neutral now and the dimming does not work.
    – Tim Dee
    Commented Nov 1, 2022 at 18:29

3 Answers 3

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Well, I never figured out the real answer, but I ended up having to remove and replace all 8 recessed lights and replace them with new ones. Once I did that, all 8 new lights started dimming on the new switch.

Thanks for all the tips!

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LED dimming is a tricky business. While there are some general standards, compatibility is not complete, as you know, between all brands/types of lights and all brands/types of dimmers.

I know this is a little late here, but it is possible that an equivalent smart switch from the same brand that worked as a simple dimmer (https://www.casetawireless.com/us/en). That is not an option for everyone - in particular, if you already have one brand of smart switch elsewhere in the same house then using a different brand in another part of the house, and therefore needing two phone Apps, two web pages, etc. for remote control isn't necessarily a great option. But if you don't have any other smart switches then before replacing 8 light fixtures it would make since to try a different brand of smart switch, especially if there is reason to do so based on a previous non-smart switch.

(Not an endorsement of Lutron per se - the exact same type of problem could happen with a different brand of switch and a different brand of light fixture.)

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I am suspecting that the new LED fixtures do not have their electronic drivers grounded. since they are just wired to hot and neutral through the plug in connection that is screwed into the old bulb socket. The new smart switch runs electronics through circuits that have built in resistance using the ground. ( we are talking milliamps) When you added a bulb it provided the electronics a ground through the old can fixture. Depending on the design of the new LEDs you may be able to add a ground from the old can to the new LED Update: additional info check out this site Dimmer info

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  • Interesting theory. Except that the installation guide I found for TP-Link Kasa shows that it requires neutral, which normally means that it does not use ground except during a fault. Commented Nov 1, 2022 at 17:06
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    Yeah I hear ya , But I have often found the guides just that... guides. I usually refer to my electronic friend...and he usually dissects things to a ground issue. But you are correct it is theory
    – RMDman
    Commented Nov 1, 2022 at 17:22
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    Correct, both the main switch and the satellite switch require neutral or they won’t work at all.
    – Tim Dee
    Commented Nov 1, 2022 at 18:25
  • For clarity here I am not saying the switch needs a ground instead of a neutral. The point I am trying to make is the smart circuitry may depend on reading a certain resistance that it cannot do with a fixture not carrying a ground. Which the new LEDs are not. I am expanding on @isherwood's answer above.
    – RMDman
    Commented Nov 1, 2022 at 20:14

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