Considering your probly a beginner and should only be keeping beginner corals (which need for the most part less light then some of your more difficult corals) something like the coralife aqualight double strip (260 watts for a 55 thats 4.7 watts per gallon with the recommened 3 to 5 watts per gallon) should work well thats what I have and I am even supporting some of the more high light corals that I was told wouldnt survive under the light I have (of corse those corals are as close to the surface as possible I think that light set me back like $200