The angle is the advertised cone angle of the optic, not half of it. I corrected this on the spreadsheet, and added a calculation for the LED current for Cree XM-L and Cree XP-G LEDs. But, I don't know how to attach an Excel spreadsheet to this post. Once I know how to do that we can include both the correction and the added calculation.

I used the Cree pdf for each LED model and derived an equation that works for most of the range of the Lumens vs current graphs here. The equations work for the 350 to 1500 mAmp range for both of them. For the XP-G the equation breaks down for lower currents, and for the XM-L it breaks down for higher currents, overestimating the lumens produced, in both cases. But, I wouldn't even consider using a higher current for either LED, just because of the cooling that would then be required for the heatsinks.

Thanks to fizzout I learned how to to this: Here is the updated calculator, for which fizzout gets 95% of the credit.

**Edit: Added Cree XP-E-Q5 LEDs which are available at DealExtreme, and which are more suitable for lower height tanks.**
Attachment 44862
**Edit:** Added Cree XR-E-P4 Bin WD (5700-6350K), which are less than $3 each on DealExtreme.

Attachment 44874