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.
TWO PHYSICAL WAYS TO CONTROL DIMMING
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.
DIFFERENT KINDS OF SWITCHES
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.
DIFFERENT KINDS OF BULBS
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.
- Should I get smart bulbs or smart switches?
- if you suspect network interference, the following FAQ may help
- 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.