After building a couple smaller RGB lamps, I decided I wanted to see how far I could take the concept. The control circuitry is basically the same, it's just a matter of using a beefier LED driver!
My finished lamp measures 30"x30" square and is 3.5" tall. It hangs 5.5" off the ceiling, and uses 9x 3W RGB LEDs controlled by a PIC 16F1829 microcontroller.
Originally the lamp had an attached control panel for color and speed adjustment. Then one day I found a perfect IR remote control with Power, R/G/B, and Up/Down buttons and even a built-in switchable backlight! I decided this would be a fun and functional addition so I wasted no time hacking the IR output signal and interfacing it to the controller.
The lamp starts out in white-light mode (like a normal ceiling light). At the press of a button, it switches to RGB Color Fading. From here, you can adjust the speed with the Up/Down buttons or even pause the color at any point in the RGB fading cycle.
Hopefully this instructable will give you some construction ideas or inspiration for your own large-scale RGB LED project!