For clarification, I perhaps someone needs to come out and say it: there are two different functions people are trying to accomplish with dimming:
1) Set and forget dimming: use a pot to manually tweak the "color balance" on your tank by increasing or decreasing the intensity of the white and/or blue LEDs. To accomplish this, you need one dimming control per bank of LED drivers that you want controlled together. In other words, if you want to dim all your white LEDs as a batch, you can use a single pot.
2) Automated dimming: use a microcontroller or some other device to gradually "fade" the lights in and out to simulate sunrise and sunset. For this, you need a PWM or variable DC voltage signal, per bank of LED drivers.
Also, there's a similar concept as far as being able to turn the banks on and off. Regardless of which type of driver you are doing, you need one power cord for each bank of lights you want to be able to turn on and off as a batch. In other words, if you want to turn all your whites on and off together, you need one power cord run to all your white LED drivers. (If you are doing meanwell drivers, or other AC-DC drivers, you just run this power cord right to each driver in that bank. If you are doing buckpucks, you'd typically have a single power cord running to one big DC power supply, then wire all the buckpucks to that power supply in parallel.)
I think one of the biggest changes LEDs will bring to the community will be in how we approach the granularity of control it gives us. If I have a tank with two metal halide lamps, I have two states for two light sources (i.e. they can each be either on or off). There's no in between. I can't spotlight a certain patch of reef, or create a "shaft" of light that lasts an hour at noon every day, or fade light from one side of the tank to the other, or follow the intensity curve of light on a real reef. With LEDs, you can get pretty much infinite control. That same tank with 2 MH lamps might instead have 96 LEDs over it, in 16 banks of 6 LEDs per bank. Now, I can dim each of those 16 banks independently, if I wish. I can also position and angle them independently, to get the EXACT lighting effect I want in the tank.
