[quote author=Stuart Faust link=topic=178319.msg1359886#msg1359886 date=1377012806]
where would i link it in?
would i use it to control the voltage going into the leds from the constant current regulator?
so
12v -> cc/cv -> ardiuno -> leds
if is is the arduino going to like 1.4a multiple times?
[/quote] Feed the PWM signal into the base/gate of the transistor/MOSFET controlling the 12V to your LEDs.
By varying the mark/space ratio of the PWM signal, you vary the brightness of your LEDS. The arduino isn't supplying the LEDs, the 12V is. All you're doing is switching (through the transistor/MOSFET) the 12V on and off very quickly using a very low current at 5V.