Dimming LEDs with 19V DC input

How could I dim clusters of 6 and 2 LEDs(so two circuits) connected to a 19vDC adapter? I was thinking that I could just use a digital potentiometer, but I dunno. And even if that is the best solution, I don't know what kind of digital potentiometer to get. Any suggestions?

suggestions?

schematic, more detail on how these led's are wired and why you need 19v on them

I can tell you this, a digital pot will not do, they only handle the same voltages as other digital parts, and they hold next to no current

what you want to be scoping out is pwm, and how you get that pwm signal from our fragile little arduino to you beefy led setup depends totally on the first part of this post ;)

haha sorry. I have 5 LEDs rated at 4.2V with a connected to the 19V/3.2A power supply with a 47ohm resistor. Then I have three LED's rated at 3.5V connected to the same power supply, but with a series of resistors adding up to around 800 ohm. I didn't want to have to reroute all the wires to the arduino, but hey, I'm no expert, so if that's recommended, thats what ill do. But it would be great if I could just add onto what I have, just to save time ;).

LEDs are just like any other load. You can drive them with a transistor or motor drive:-
http://www.thebox.myzen.co.uk/Workshop/Motors_1.html

You need to know what current the LEDs actually take rather than the current capability of the power supply, in order to select the right transistor that can handle the load.