Why would my dimmer switch only dim lights about halfway?

Question

I have a 3-way Lutron dimmer switch installed at the end of a 4-way circuit in my home (there are three switches controlling the lights to our 1st floor staircase, 1 downstairs and 2 upstairs). I don't know anything about circuits or switches; I just follow directions. That said, I'm pretty confident it's wired correctly.

I have read online (on this question, in fact) that for a 4-way circuit you need to install a 3-way dimmer switch on one of the ends. I've tried both ends (one of the answers to the above question claims it matters, though the top-rated answer asserts it doesn't), but either way the switch works but only dims lights to about 50% when the dimmer is all the way down. All the other dimmers I've installed in the house take lights down smoothly to pretty much 0% when the dimmer is all the way down, so I don't think this is working like it's supposed to.

Am I making some simple mistake? Is this a fundamental limitation of putting a 3-way dimmer switch on a 4-way circuit? Does it have anything to do with the number of lights on the circuit, or the distance between the switches (like I said, they're above and below a staircase). Or do I most likely just have a defective dimmer switch?

In case it matters, one other potentially relevant piece of information: most of the bulbs on the switch are dimmable LEDs, but there is one incandescent bulb in the middle (replaced a recessed can light with a pendant light). Not sure if that could be responsible for screwing everything up.

Answer 1

Most new dimmers rated for CFL/LED use have an adjustable low-point setting. Check and see where yours is set.

Refer to the "Dimming Range Adjustment" section of the instructions here: http://www.homedepot.com/catalog/pdfImages/cb/cb27dfa7-40a6-4788-9112-c2a619a4b2e0.pdf

Answer 2

A dimmer might be built with one of several circuit types: Leading edge, trailing edge, and sine wave dimming. See here.

What that boils down to is that the cheaper dimmers use cheaper designs and so don't have as broad a range as more expensive dimmers. In particular, the cheapest dimmers are in series with the load and have no neutral reference, so the more dimming called for, the more "off" the dimmer electronics are. That is, at minimum power, the dimmer is limiting the current flow so much the dimmer itself doesn't have enough current to function.

In a 3+ way dimmer, there probably aren't as many (easily available) choices of electronic design used. It likely is easier to obtain acceptable results by adjusting the wattage of the bulbs (by swapping them out) so that the total load is close to about 80% rating of the dimmer.

That is, for a dimmer rated at 400 watts, the ideal load is about 400 w x 0.8 = 320 w. If only 10 watts were on the dimmer (which is now readily possible with LED lights), the dimmer will not work at anything other than 0% and 100% settings. With 200 watts, it might work from 40% to 100%, etc.