I have the price of this project down to about $150 now, so I am starting to order parts. I plan to use 24 Cree LEDs, ordered here:
http://www.dealextreme.com/details.dx/sku.2395 in an array of 3 rows of 8 each, on a grid of about 24 inches by about 6 to 9 inches. Here is how I arrived at this:
I spent a lot of time on
http://www.nano-reef.com/forums/inde...c=188085&st=20 and a couple of others. This particular thread gave me some good data to use to calculate what I would need for my tank and to get the PAR I want. So, I plotted the data on log log paper so I could extrapolate it:
This data is from 11 Cree LED's in an array that is 42.5 square inches, and it would give 240 PAR micromols at the 17 inch distance I will use. I will be illuminating about 450 square inches, so, assuming that the illuminated area that the data is from is the same size as the array, to be conservative, I will need 450/42.5 times that many LEDs, or 116, to get the same PAR. But, I only want about 50 PAR, so I need 50/240 times 116, or 24 LEDs similar to those used in the reference. I chose somewhat less efficient Q2 Cree LEDs for cost savings, and because of the conservative calculation I did above.
More to follow.