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I have a 'Sputnik'-style ceiling light fixture that accepts about 12 bulbs. I installed 12 LED bulbs into the fixture. However, the fixture was just too bright with 12 LEDs, so I installed a dimmer switch later that evening. The LED bulbs are supposed to be dimmable and the Amazon reviews for the LEDs indicated that people were having success with Lutron and Leviton dimmers. I bought a Leviton Decora smart dimmer.

After installing the dimmer, I found that that the LED bulbs would not dim, they would only turn on or off. I verified that the Leviton app had the bulb type set to 'LED'. To troubleshoot, I decided to remove one of the LED bulbs and replace it with a 60W incandescent bulb. I knew that the incandescent bulb would be capable of dimming.

To my surprise, not only did the incandescent bulb dim, but the other LEDs started dimming as well. If I remove the incandescent, then the LEDs stop dimming. If I install a 20W incandescent, then the LEDs do not dim. It's only when I install the 60W incandescent that all of the LEDs start dimming properly.

How is it possible that the LEDs only dim when a single 60W incandescent bulb is installed in the same fixture?

Edit: these are the LED bulbs (6W each) and this is the Leviton Decora dimmer switch (300W max for LEDs, 600W max for incandescent.

  • Some dimmers only work well with compatible bulbs. Leviton should publish a list of LEDs that are compatible with their dimmers. I have Lutron dimmers and some of the cheap "dimmable" LEDs I bought on Amazon would not shut off completely. They were not on Lutron's list of compatible lamps. I bought some that are on their list and they work fine. – ArchonOSX Jan 15 '18 at 10:39
  • That's pretty much an answer @ArchonOSX especially with the personal experience attached to it. Yes, cheapie/Cheese/Utilitech/Feit/LoA bulbs are pretty unreliable. – Harper Jan 15 '18 at 15:35
  • @Elliot B. can you link to the Amazon product page for the bulbs and dimmer and tell me the wattage of the individual LED bulbs? The comment from ArchonOSX may point to your issue, but it's speculative since we don't know what the products are. – Sam_Butler Jan 15 '18 at 18:24
  • @Sam_Butler These are the LED bulbs (6W each) amazon.com/CMYK-Dimmable-Squirrel-Filament-Decorate/dp/… and the Leviton Decora dimmer switch (300W max for LEDs) amazon.com/Leviton-DW6HD-1BZ-Incandescent-Required-Assistant/dp/… – Elliot B. Jan 15 '18 at 19:17
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In general, dimmers have both a minimum and a maximum load. The most common reason for low loads not to dim, is that they are below the minimum for the dimmer to function. By adding more load, the dimmer begins to function properly. This is further explained by lighting manufacturer Lighting Services Inc (LSI):

Minimum Loads

Dimmers have minimum load requirements because if the LED load isn’t drawing enough current to keep the dimmer’s switching elements closed, the dimmer will have unpredictable behavior. This behavior can include flickering, reduced dimming range, flashing when off, or not even working at all.

Dimmers that are designed for incandescent loads tend to have a larger minimum load requirement because incandescent fixtures generally have higher wattages than LED fixtures. This means that these dimmers will most likely require multiple LED fixtures to meet the minimum load requirement. Testing is necessary to determine the exact number of LED fixtures needed for each incandescent dimmer. Dimmers that are designed for LED loads usually have a lower minimum load requirement and typically only require one or two fixtures. The LED minimum load rating for LED load dimmers is usually given in number of lamps instead of Watts (W) or Volt Amps (VA).

According to Leviton's product page for the DW6HD-1BZ wi-fi dimmer:

It uses the latest generation of Leviton’s dimming technology for smart lighting control for a single LED bulb in a hallway or a strand of holiday lights, ensuring LEDs do not glow when off.

Based on this, it should be possible to perform low-range dimming of low-power LED loads with this dimmer.

The instruction sheet that accompanies the dimmer refers you to a list of compatible LED and CFL bulbs on Leviton's website, a 2015 version of which I found here: http://communities.leviton.com/servlet/JiveServlet/previewBody/4385-102-1-7048/Decora%20Rocker%20Slide%20Dimmer%20Compatibility%20Chart.pdf

Based on the Amazon product title for the bulbs you purchased, which contains the grammatically-incorrect phrase, "Light For Decorate Home", I can assume that these bulbs will not be from one of the manufacturers Leviton have tested and confirmed as compatible.

That being said, the same page lists Leviton IPL06-10Z, DSL06 and VP0SR-1LZ dimmers as compatible with those bulbs. Given that Leviton is a well-respected brand, my recommendation would be to trust their statements over those of the blb vendor/manufacturer and purchase new bulbs that Leviton lists as compatible. If you do not wish to do this, you may choose instead to contact Leviton and seek technical support based on the dimmer's inability to meet the description above.

  • I would say if purchased on Amazon and the sales pitch says they will work go for it. Amazon has been good about returns for stuff that dosent work. The bulb manufacturer may have tested their lamps with Leviton dimmers because they are on the big hitters when it comes to switches and outlets. – Ed Beal Jan 15 '18 at 19:57
  • I'm familiar with the compatibility lists and the risk I was taking by purchasing LEDs not on the list. What I'm curious about is why the LEDs started to DIM only when I installed an incandescent bulb alongside the LEDs in the multi-bulb fixture. Any idea why that would be happening? – Elliot B. Jan 15 '18 at 20:30
  • @ElliotB. I've edited the beginning of my answer to address this more explicitly, I hope it's helpful. – Sam_Butler Jan 17 '18 at 0:27
  • @Sam_Butler It's possible it could be a minimum load issue, but that seems unlikely. This fixture takes 12 bulbs and the dimmer is supposed to work with LEDs -- so one would think the dimmer should expect to handle a power draw less than what my fixture is drawing. – Elliot B. Jan 17 '18 at 1:15
  • As I say in my answer, the dimmer should be able to perform such low-range dimming, but the observation is that it isn't doing so. 12 x 6W = 72W; 11 x 6W + 20W = 86W; 11 x 6W + 60W = 126W. Your dimmer works at a load of 126W, but not at 86W nor 72W. Therefore the answer is that minimum load is the reason this would happen, and according to the manufacturer it shouldn't be happening with this dimmer. Far from unlikely, it's the only explanation anyone has given and it is well reasoned. – Sam_Butler Jan 17 '18 at 1:38

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