The electrician has been correspondeding with Nayuta, manufacturers of constant current power supplies, and they had the perfect model, with the right voltage and the right range of currents that could be varied. The problem was, they did not know how to vary the current. The power supply has a screwdriver trimmer wheel on it, and there are terminals to connect something to vary the current, but they do not have the something, nor could they, or the electrician, find one. If you can understand that, please explain it to me, because it does not make sense.
I also found some power supplies from AudioQ (Japanese only), with volume controls, which looked promising. They put out up to 350 milliamps, which should be about right for a 12 volt, 4 watt bulb, between 2 and 26 volts.
We want 3 bulbs on one circuit, which at first I thought would be no problem--they would just not come on at full brightness. Then I remembered the VI curve for LEDs and that the D is for diode. If there is much less than 12 volts going through each LED, or 36 volts total, then they will not come on at all, however many amps are available.
So this would only work if we had two bulbs on each circuit. Also, the electrician seemed much happier with something in a box, rather than having to install a bare circuit into the wall.
There is another nagging worry though. Even if the current could be adjusted, and the voltage kept at suitably high, would the bulbs actually respond properly, or would their circuits mess things up?
I'm sure the parts must be out there somewhere, but after a few months of searching we haven't been able to find them, so it's time to go to plan B, which is to use a standard voltage dimmer switch, get LED bulbs that work with dimmer switches and hope for the best. The danger with this is incompatibility between dimmer and bulbs, leading to flickering. As there are three bulbs, one of them may flicker at any level, and we'd be left with an elaborate on/off switch.
I'm about to order some lumilux fully dimmable LEDs from EarthLED, which apparently work with magnetic transformers and dimmer switches. These seem to be available, although the electrician's first suggestion was a switching power supply and a pulse wave modulation (PWM) dimmer switch. As each of these, and no doubt the controller within the dimmable LEDs, are electronic circuits, each with their own frequencies, the chances of interference, harmonics or beats is quite high.
Not at all relevant, but here's another constant current, non-variable, power supply.
