Re: adding the third LED out of four caused the dimmer to stop working?
Dollars to donuts it's a compatibility issue between the dimmer and the LED bulbs.
The dimmer is a standard incandescent dimmer which works fine for what it was designed to be used for --- simple resistive element load of incandescent lamps.
However , with LED/CFL lamps they have finiky electronic circuitry that produces a reactive load to the dimmer. The electronics of those LED/CFL lamps are sensitive to the way the standard incandescant dimmer outputs the manipilated duty cycle to the lamp --- incandescant lamps aren't as sensitive which is why they work fine.
Quality of the dimmer is also a factor. Cheap quality dimmers can have more hysterisis reaction to line and load along with more radio interference --- which also plays havoc with LED/CFL lamps --- than a high quailty dimmer.
To add , different manufacturers lamps will react differently because of design and component differences.
There are manufacturers of lighting controls that are making dimmers specifically for LED/CFL lamps.
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