Whats the best light for a 180 gallon ?

it all depends on what you are trying to accomplish. add these details and you will get a better answer: what kind of tank? Fresh or salt? If fresh, planted or not, if salt reef or show (fish only) do you have an enclosure/canopy? do have a top or want hanging? do you want bulbs to fit your existing housing or redoing completely? what is your budget? with what you have on aquarium that size for what is seems like you want I would at least double what you have (if I read right you have 2 36" bulbs or do you have 2 36" twins for 4?) for starters-- I would want at least 8 36" (4 sets twin) see example http://www.aquarium-supply.biz/72_T5_HO_8_Lamp_Fixture_Lunar_Light_AquaticLife_p/ral01038.htm that one is for reef but come for fresh as well and come a lot cheaper too, just wanted you to see style