Nope, no formula to it really. You can go with a wider reflector so you spread the light more... for instance, use a 90* reflector optic instead of a 60*. This spreads the beam of light out to make it less intense. You will want to go with at least 3w LEDs... I'm not really up to snuff on the ins and outs of the different Bins and manufacturers, but there are others who are. I would search on here for LEDs and see what you come up with, there have been a few discussions concerning them as well as a few links to other DIYers threads.