Thanks for the input! I figured it would be alot of light and likely overdoing it, but are you basing that on Crees? The Bridgelux don't have as much oomph as the Cree LED's from what I have read. What kind of PAR values would 5 Crees vs 5 Bridgelux have at the substrate?
Bottom line is that I have to go with atleast 12 LEDS because the driver I have is for 12-20 LEDS. With this in mind, my rationale for it being doable is that:
1)the bridgelux don't produce as much PAR as the Crees
2)I can dim the fixture
3)I can raise the light as high as I want
In terms of first hand experience, I have been playing around with the fixture (32 LED's) for the last couple of weeks over my reef tank and the dimmers do quite a remarkable job...at the lowest setting my mushrooms would start reaching up for the light which never happened with my 4bulb T5HO odyssea fixture. This suggests to me that the light level for 32 Bridgelux LEDs (dimmed to the minimum) is less than the T5 4 bulb fixture. I am currently running 2 T5 bulbs (Odyssea) over my shrimp tank with no problems so 13 Bridgelux LEDS dimmed to the minimum should be less than the 2 bulb fixture.
Alot of assumptions I know...but my goal is too have a highly versatile fixture that will be usable over a wide range of tank sizes and light levels. If it proves to be way too much light, I can order a new driver and take out some LED's...or get a bigger tank for it haha.