Dimmable LED's: what am I doing wrong?

December 2, 2014 10:09 AM

I've installed new LED-compatible dimmer switches. But I still find that the dimmable LED's I've bought don't dim all the way.

A year ago I posted this question on dimmable LED's.

It doesn't seem to matter if there are LED's and incandescents on the same switch -- if I remove the incandescents, the dimmer still doesn't go down to zero.

Is this because the dimmers are switchable dimmers (i.e. you can switch them on and off, not just up or down) and those don't go to 0?

How do I get down to truly dim lighting?

posted by musofire to Home & Garden (6 answers total)

So, you're saying, when it's "fully" dimmed on the dimmer, the light is still on? I'll have to try that with my LEDs at home tonight, but I wonder if it's just that the LEDs have so much lower of a power requirement that they can stay lit with much less current than an incandescent can? I know that in my previous house, I had some incandescents on a dimmer similar to this one, and when it was pushed all the way to the bottom, the lights appeared to be off but would make a faint buzzing sound, so they were still getting some power.

Also, what specific dimmers and LED bulbs are you using?
posted by primethyme at 10:14 AM on December 2, 2014

LEDs will not dim as low as incandescent. It's just a function of the technology. You may also find that depending on the bulb/dimmer combo the light will flicker on the lowest setting. This is due to the fact that the dimmer sees the bulb as drawing so little power that it will shut it off while the bulb "sees" the shutoff but basically continues to draw power.

Anyway...long story short, you will not get LEDs to dim like incandescent bulbs. I have LED recessed lighting in the kitchen, 2 hallways, living room and bedrooms. The living room lights will dim on lowest setting with no flicker. The hallways will sometimes "flash" when turned on then go to the set dimmer level. The kitchen will flicker on the lowest setting. The bedrooms are fine.

All this is a function of the low level of power draw from the LED bulb itself. In the end no matter how LED compatible the dimmer is I don't think the technology is there yet to replicate incandescent.
posted by eatcake at 10:16 AM on December 2, 2014

Response by poster: Thanks for asking, primethyme. The specific combination is:

Dimmer: Leviton Sureslide LED/CFL Universal Dimmer
Bulb: Luminus Max LED Par 20 Dimmable 8 watt bulbs (replaces 50W halogen).
posted by musofire at 10:19 AM on December 2, 2014

As already mentioned, LEDs won't dim down all the way to nothing like an incandescent bulb. However, many brands can dim to a very low level - the Philips bulbs I own all dim to around 1/8th of their output, with the warm glow of a dimmed incandescent, which is about the lowest point where the light is bright enough to be useful in the room but still extremely dim. Unfortunately, the specifics of how dim any given bulb can get does depend on the design of the specific bulbs, and minimum light output is usually not advertised.
posted by eschatfische at 10:25 AM on December 2, 2014

Best answer: It will never (and shouldn't) dim down to 0 - that's not the desired property of this switch (to get it to 0 you are supposed to turn it off). That said, though, the dimness level is adjustable. According to the instructions I found online here:

Setting Minimum Light Level (Programming mode)
1. Ensure the dimmer is set to the OFF position.
2. Set the bulb selector switch to the LED/Incandescent position.
3. Push rocker switch to ON position.
4. Set the bulb selector switch to the CFL position.
5. Raise or lower the slide control level to achieve the desired minimum light level.
6. Set the bulb selector switch back to LED/Incandescent position.
7. A momentary flash of the bulb will occur confirming the new setting. 8. Push rocker switch to the OFF position.
9. For dimmable CFL lamps you must return the bulb selector to the CFL position.

I just installed a Lutron branded LED/CFL dimmer that had a little adjustable knob to set the desired lowest level. But again, this level shouldn't be 0 - it should be the lowest it will go before it starts flickering.
posted by brainmouse at 10:59 AM on December 2, 2014 [1 favorite]

The minimum dimming level of leds is normally 10% of full output. This is usually specified in the data sheet but these appear to be cheap Costco generics and I can't dig up a sheet for them. Anyway, you won't get to zero and you should be switching them off when you don't want them in any case.
posted by deadwax at 12:54 PM on December 2, 2014