Just made up a LED Luxeon array to test
( mix of blue and red 3W LEDs).
As far as the spectrum I am using this chart...
Botany online: Photosynthesis - Absorption Spectra - Chlorophyll a and b
Since I am concerned about power cost I matched the number of LEDs and type ( Red and blue have different voltage drops ) to equal 12V so no dropping resistor is needed.