FAQ Request: Dimmers, Smart Bulbs, Flickers, Buzzing

I see a lot of topics where being able to point to a FAQ on this topic would help a lot. I’ve got a few personal rules of thumb for lighting installations, but I thought it would be a lot better if someone who’s written one of the ST dimmer handlers wrote it so they could mention anything ST or Smart App specific. So this post is definitely a request for a FAQ, not a FAQ itself. But just to get things started…Feel free to use, edit, or toss any of the following.


Dimming is either controlled by the amount of current the switch sends on the wire to the bulb or the amount of current the bulb decides to draw from the wire.


A switch that controls the amount of current sent may be networked or not.

Some switches don’t control the amount of current sent–they send a command asking the bulb to change the amount of current the bulb is drawing. These switches don’t even need to be on the same circuit as the bulb. They may physically look like a regular switch, but the instructions are being sent by radio wave to a receiver in the bulb.


Bulbs can be incandescent, LED, Dimmable LED, or Smart LEDs. The first 3 types dim based on the amount of current they receive. More current, brighter light.

The Smart LEDs, however, dim by deciding how much current the bulb is going to draw. Usually these are most efficient when the current available is high and the bulb itself is deciding how much of it to use.

(One additional caution when using smartbulbs to replace dumb bulbs in existing fixtures… @Sticks18 has pointed out that there is often a warning deep in the fine print for these bulbs that they should not be used in totally enclosed luminaires as they may overheat.)


Incandescents need to be matched with a switch that will change the amount of current the bulb receives on the wire. The switch can be networked or not as long as it controls the actual amount of current flowing to the bulb.

First generation LEDs and dimmer switches confuse each other, usually resulting in flickering, buzzing, and the bulb sometimes not turning on at all.

Second generation “Dimmable LEDs” that are not smart bulbs can be used with most of the same dimmer switches that control incandescents, although there may still be some hum or buzz at the lower levels. A few buzz at the highest levels in certain fixtures. They work the same way as the incandescents: the switch increases current flow and the bulb gets brighter.

Smart bulbs, though, work by the bulb choosing how much current to draw. In general, they match up best with switches that can’t themselves change the amount of current sent. So usually you don’t match a smart bulb with a dimmer switch. A smart bulb matched with a dimmer switch that can change current levels almost always results in flickering, or even bulbs that appear to randomly turn on and off. It can also burn out the switch itself, which can cause additional electrical problems.

The alternative for smart bulbs is a switch that doesn’t control the current, but rather sends radio commands to the bulb. It doesn’t matter whether this is a keypad/remote with different “scenes” or a switch with a slider as long as the current level to the bulb stays the same and the switch is sending radio requests for the bulb to change the draw.

Or you just use a smart bulb with a dumb toggle switch, leave the switch turned all the time so the bulb has current to draw from, and control the bulb from a mobile app, tablet dashboard, or through automatic scheduling. (Many people put switch guards or childproof locks on the switch to keep guests from turning the current off.)


Flickering can have multiple causes.

You might have a bad matchup, like a smart bulb and a dimmer switch that changes current strength. Or a first generation LED and any dimmer control.

Someone might have manually turned down a dimmer switch that controls current strength to smart bulbs, making it difficult for the bulbs to follow the commands sent to them.

You might have something else drawing extra power from that circuit occasionally, like a microwave or hair dryer or fan. (Older GE/Jasco networked dimmer switches were particularly sensitive to changes in draw to the circuit as a whole.)

You might have interference with the radio signals to a networked switch or smart bulb.

You might have a physically bad bulb, fixture, switch, or wire.

There are also some issues specific to network traffic and dimmer switches that control current strength. Changing a switch’s schedule, adding new bulbs or lamps, even just sending a message to ask the switch which lights are on (polling) can cause some dimmers to reset their inner timers, creating unexpected results.

The first thing I personally always check is is there an efficient matchup between switch type and bulb type.


  1. Should I get smart bulbs or smart switches?
  1. if you suspect network interference, the following FAQ may help
  1. best switches to use with smart bulbs

Anyway, that’s just some basic lighting installation stuff, independent of SmartThings. If someone else could add a ST specific context, particularly if there are any UI or smartapp issues, I’m sure that would go a long way towards making it a real FAQ.

  • note: I didn’t bother to distinguish between a controller that communicates directly with the smart bulb and one that sends a request to the hub which then sends the request to the bulb because it doesn’t really affect the outcomes discussed here. A light not turning on at all might benefit from direct association with the local controller, but it would be really rare for flickering to be an issue that could be solved by direct association.

The following video shows a Z wave light switch that doesn’t require a neutral (the GE switch in the video has been discontinued, but Cooper still makes one) tested with four different kinds of bulbs:

A conventional incandescent,
A conventional CFL,
A dimmable CFL,
And a white only dumb LED bulb

They didn’t test a smart LED.

Even in this very simple test, you can see the flickering problems with the CFL bulbs.

The plain white LED actually works pretty well, although not as well as the incandescent.

I still think it’s best to use a neutral wire, but it is possible if you only have the two wires available and you get the right switch and the right fixture and the right bulb.

We should also note that sometimes you’ll only see flickers at full on or below 25%. There are many people who only dim between 50% and 90%, so they might not see flickers while someone else who uses a wider range does. This is why sometimes only one person in a household will complain about flickers.


Hey JD, wasn’t there somewhere you mentioned that some devices like the GE 12724 dimmer required a minimum load and that when switching to LED’s, you might find that the load is high enough?

Trying to work out if the 12724 is going to be okay attached to one LED bulb…

Yes, most dimmers require a minimum load and that can cause issues. It should be in the device specs.

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So interestingly, looking at this page:


Minimum Load: 40W”

That being said, having looked at the actual documentation, it doesn’t specify a minimum load anywhere?

That definitely holds true in my house. The dimmers in my house are mostly old which were not meant for LED. Typical example are the ceiling fans with lights which can be dimmed. 4 bulbs (Candelabra Base). Once I changed those to LED’s, it flickers when dimmed and/or does not tun off completely. Same thing happens with my recessed lights dimmer. Places where I have 40W plus in LED (multiple bulbs), I do not have flickers even with the vintage old dimmers.

But I don’t think this should apply to the newer dimmer these days. The CFL/LED compliant ones.

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So I have a GE 12718 connected to one ‘vintage Edison’ style LED bulb, specifically listed as dimmable however, it buzzes the instant you dim at all (< 100%) and it starts flicking when you get down to about 50%, itwill dim lower than it can turn on.

So for example I can dim it below say 10% and it will stay on (buzzing and flickering) but if I switch it off, it won’t ‘light up’ again until I turn the dimmer up to say 25%

I use Globe smart bulbs in my home for Alexa. They have been amazing & changed my life since I got them as a gift @ Christmas.
But recently one of them has started “glowing” or flashing randomly when it has been turned off. I will wake up in the middle of the night to it flashing like a fire alarm type of flashing or just a low glow.
Neither of these can be stopped by turning the device off or on, uninstalling/reinstalling.
Is this an indication that the light is near burning out already? It seems unlikely since it’s only been 4 months & it is supposed to be an energy efficient bulb.
The wall switch that controls the plug & the lamp stay on.
How do I stop this?

If it only started recently, it’s most likely the Bulb failing. I would contact the manufacturer.

The only other likely alternative would be if you recently added a new device to the same circuit like an air purifier or a window air conditioner that might be making heavy use of the circuit. To test that you could move one of your other bulbs of the same model to the same location and see if it shows the same flashing behavior. if it does, the problem is not likely the bulb, it’s something environmental on that circuit.

But if the second bulb is fine in that location and the first bulb is not, then, yes, it sounds like the bulb going bad. So again, check with the manufacturer.