i have 3 VHO and 24 PC lights on my 55gal/with custom canopy. so i would say you could probably get away with 6 or 8, and that is A LOT of light. my icecap endcaps mounting brackets are 2 1/2" and the bulbs are 1 1/2" wide. i have the URI bulbs, but am getting a coralife VHO 10000k tomarrow. then i will be running 1 10,000k, 1 white actinic, and 1 super blue actinic on the VHO's and 2 50/50 PC's.