Parallel connected LED lights -last one is dimmer, why?

Question

I have 3 Lutron LED recessed lights (9W) with individual driver each(came with the lights) connected in parallel and wired to a Lutron dimmable compatible switch.

For some reason when switch is set to full dimm mode and turned on, the last LED is not coming on. When it's set to anything a bit brighter than full dimm it comes on but slightly dimmer. The first 2 lights are working great.

When I start on full power and then go all the way down to full dimm the third light stays on but also slightly dimmer.

When turning off on medium dimm level, the first 2 lights go off immediately and the last one takes a bit to turn off. As if it's continuing to use residual electricity or something :/

Lights are feeding from receptacle which is on 15A circuit.

The connection is as follows:

What could be the cause for this behavior?

Answer 1

Not all mains powered LED lights are compatible with all types of dimmers. And when you do happen to get a proper LED compatible dimmer with dimmable LED bulbs/drivers it is not uncommon for not all of the lights to work exactly the same.

If you were to swap the positions of two of the LED bulbs/drivers that you have installed you will most likely see the aberrant behavior of the one LED (like your last one of three) move with the bulb/driver and not be related to the position in the circuit. There are a couple of good reasons for this:

1. The amount of energy used by each LED bulb/driver is so small that there is not going to be any appreciable voltage drop along the typical 12AWG wiring that is used to hook up a string of three lights. That of course assumes that all the wire interconnections were made with really good quality wire nuts and good workmanship so as to eliminate a high resistance connection.
2. The circuitry used in each LED bulb/driver is not going to be a precision designed circuit with carefully tuned behavior with respect to how it reacts to the chopped AC voltage waveform produced by the dimmer unit. Unfortunately the circuits used in LED bulbs/drivers is typically produced in a way that keeps cost to a minimum. This will result in the various bulbs/drivers having different thresholds of chopped AC waveform where they will come on or turn off.

The best advice, if the behavior that you are seeing is too annoying, is to swap in additional LED bulb/drivers until you find a set that all operate to your satisfaction. This need not be an issue having to purchase extra LED bulbs/drivers because in many cases of converting a home from the older incandescent lighting to the energy saving LED lighting you will have some lighting circuits that only have a single light position. You can place units that didn't play well in a group at these locations. And in some cases if the dimming behavior of some units is objectionable you can choose to equip those particular lighting circuits with full on/full off switches instead of dimmers.

I have recently done a 100% conversion of my house over to Lutron smart switches and smart dimmers. I have experienced first hand results of how various LED bulbs and some light fixtures that drivers+LEDs react to being controlled by a dimmer. In several cases I veered away from using a smart dimmer in favor of using a smart on/off switch for the reasons mentioned above. I also experienced some LED bulbs that gave out distinct noise when operated at a dim setting and so replaced those with newer LED bulbs that had a better dimmer compatibility. (This latter has occurred because some lighting positions were changed to LED bulbs a few years ago when regular manual flip toggle switches were in use and the earlier bulbs were just not as dimmer compatible). And finally in some lighting fixtures where there are multiple low wattage bulbs the decision is to stay with incandescent bulbs because of the desire for all the bulbs to exhibit uniform behavior when power to that fixture is controlled by a dimmer. I have not yet addressed two multi-bulb fixtures that use halogen bulbs. These work nicely with the smart dimmers but eventually I will want to look at converting those over to energy saving LEDs. I may be looking at having to do fixture replacement if I end up having problems with multiple parallel halogen->LED replacement bulbs. In that case the most viable solution will likely be a new fixture that uses multiple low voltage LEDs that are sourced from a single driver.

Answer 2

The answer was a bad ballast. Once the offending light was changed including ballast the fixture works as expected with no delay and no dimming issues.