Okay, why even stack LEDs when you can buy 1 10w LED from LedEngin?
Now I am thinking about putting 1 BLUE LED (LZ1-10DB05) and 1 RED LED (LZ4-00R215, this is a 15w device).

Would it be okay to assume that the luminous power efficiency of the LedEngin High power lights is about 20%, meaning that 20% of the electrical power is converted into light energy?

Thanks again veggi, this is what has been bugging me since I started working on the controls for the Luxeon K2 and the Luxeon III.

Now I am thinking of just having 12v across each high power LED bank with space for a relay or transistor that I can add in the future.

EDIT: A lot of these devices are back ordered.