Why does my LED light flicker when turning it on using a dimmer switch?

Question

I replaced a flushmont light fixure with a new dimmable LED Flushmount. I also replaced the old switch (see images below) with a dimmer switch. When I turn the LED on there is a flicker while it is turning on. After that initial dimmer it seems to work fine and the dimming feature works well.

Here's a video of the light turning on.

The dimmer switch that I installed is a toggle dimmer (this one) with 2 brass screws, one copper screw, and a ground wire. There was no ground on the old switch, so I connected one black wire to one brass screw, the other black wire to the other brass screw, and the blue wire to the copper screw. Since I am using this as a single pole switch, my understanding is that it shouldn't matter much.

My questions: 1) Is this simply due to having a single LED light on a dimmer? 2) Should I be concerned about my connections in the flushmount fixture or switch? 3) The old switch had the two black wires under one screw. Should I do the same on one brass screw in the new switch?

Thank you for any help!

Answer 1

Connect it electrically the same as before

Based on the pictures, the original connection was:

• TWO black wires to one screw
• A blue wire to another screw

In that case, the blacks are both hot. One is the incoming hot, the other is an outgoing hot to another location. That is a little odd because there is already a wire nut, so instead all those wires should have been connected using the wire nut with just one short wire (pigtail) to the screw. Under most circumstances, you should only have one wire per screw.

The blue wire is switched hot.

The new dimmer only needs two wires, unless it is used as part of a 3-way switch (i.e., 2nd switch elsewhere).

The instructions are not terribly clear in certain respects. However, it is pretty clear that for a single (not 3-way) switch, it does not matter which wire goes in which screw, as long as you put one wire on one color screw and another wire on a different color screw. Therefore, you put a black wire (just one, more below on that) on the screw that is a different color from the other two screws and the blue wire onto the screw opposite that screw (i.e., other side of switch rather than above it on the same side of the switch). That gets you hot and switched hot connected properly.

Now to the second black wire. The instructions actually say "Your wall switch may have two wires attached to the same screw. Tape these two wires together before disconnecting." but then never (as far as I can tell) actually says what to do with the taped wires. Taping is not a valid way to permanently connect wires, and I don't think they actually meant "tape together electrically", but rather "tape together so you know where each of these wires that all look the same should go". In this particular situation, what you need to do is wire nut the two wires together and attach a pigtail (short piece of same colored wire) to the screw. Since your picture already shows a wire nut & pigtail, all you actually need to do is move the "extra" wire (the one that was originally on the screw and is not a pigtail) to the wire nut with everything else.

By connecting one black to one brass screw and the other black to the other brass screw, you effectively treated your hots (plural) as if they were travelers (used between 3-way switches). What that actually did (I think) is something like:

• switched hot became "common"
• hot (incoming) became "traveler 1"
• hot (outgoing) became "traveler 2"

When switch is in "traveler 1 ON" mode:

• common connects to traveler 1 == Light on
• traveler 2 OFF == something elsewhere in the house isn't going to work

When switch is in "traveler 2 ON" mode (which is the same as "traveler 1 OFF" == "just flip the switch":

• traveler 1 OFF == Light off
• common connects to traveler 2 == everything else in the house works normally

As far as the blinking when turning on the light, I suspect that is simply the way the bulb is handling the initial signal form the dimmer. It is possible that other bulbs will work better, but hard to say. Dimming LEDs is a tricky business - almost amazing that any of them can dim at all when run on AC.

Answer 2

I have had flicker problems with some combinations of LED's that were rated for dimming and different brands of switches that were rated for dimming. Your specific brand of led may be the problem. Check the instructions for your dimmer and see if it has your led listed as compatible. The wire on the 1 screw looks to be looped not 2 separate wires (2 wires under a screw like this would be a code violation). If your new switch has screws do the same if it has leads run the lead to the pigtail. If leads on the new switch you might need a larger size wire nut I cannot tell the color of that one. But verify the LED compatibility and that is probably the root cause of the flickering.

Answer 3

You should have the installation instructions but they are here if you tossed them.

The first thing that jumps out at me is this note:

Helpful Hint: If you are replacing a single-pole switch, the screw on the same side as the different-colored screw is not used

Which is a great achievement in confusingly worded instructions. Here's what that means: You only use one of the screws on the side with two screws for the single pole function. It doesn't really matter which one other than which position will be 'on'. If you use the brass screw on the side that doesn't have the copper screw, I would expect on to be the 'up' switch position which is what people expect. Some pictures might help:

A single-pole switch is simple. Open is off (current can't flow), closed is on (circuit is connected):

A three way switch is slightly different in that each position makes one of the load sides screws hot. Up position makes brass screw that is alone hot (I think) and the down position makes the brass on on the side of the copper screw hot. The copper screw is where you are supposed to attach the source hot from the circuit based on the diagram from the instructions. You need two of these types of switches to make that work as shown here:

But since this is a single-pole configuration, you don't care about the second screw. You just need one. You can ignore the other one but it's not a terrible idea to tape it because it will be hot whenever the light is off.

The fact that the two black wires were under one screw means that one is a pass-through for power to something else. Something that was always on is now on this switch that was not before. You need to connect those two black wires again. A wire nut and a pigtail is the correct way to do this.

The blue wire is what goes to the light. You reconfigured this incorrectly but that's not causing the flickering. If the dimmer is set to low when you turn it on, it can either flicker or not come on at all. You might get better results if you turn it up to full brightness first and then lower it.

Answer 4

I tried all of the suggestions above and the issue persisted. I am convinced that the LED light with the dimmer is the problem (which most folks seemed to agree on). It is odd to me that the flicker only occurs when I initially turn it on. Typically I seem flickering issues with LEDs to be constant while they are on.

Regardless, I purchased a standard single pole switch and all is well. Looks like dimming just isn't going to be an option in that room.

Thank you all!

Answer 5

Modern LED bulbs mostly use switching power supplies, which charge up a capacitor to a specific voltage, run the KED from that, and recharge them when the voltage drops low enough to need a recharge.

If the input voltage is too low, it may take several AC cycles to charge the capacitor enough for the LED to light, and the bulb will flicker.

Note that this becomes more obvious when you have a fixture with many LED bulbs close together. Limits on inrush current and sanple-to-sample differences between bulbs can cause some interesting interactions when the dimmer is set close to or below that needed to keep everything charged up.