Large LED display control

Hi all, I am building parts of the set for a show. In particular I am making a large LED sign using 600 odd LEDs in 3 channels. What I wish to build is a simple way to dim these LEDs with a FET of some sort. What I do not know is whether I need to make a current limiting circuit or will a voltage control work fine for 200 odd LEDs at ~12 v. (5mm red leds ~30mA max current each) Also the control setup I use will be Arduino generated DMX but fed through a demux which will give me a value of 0 - +10v per channel corresponding to 0 - 255 dmx values.