well the cfm's are measured by an unobstracted push/pull. so your 500+ cfm fan has now been cut in half just with the bulb, and then the block that you have at the other end. I could be wrong, but i would definitely look into that as far as how much air your sucking out and then how much air your pushing in. Just a thought is all, other than that, i think your doing a great job....keep up the good work.......