I have a 30" tall tank and the key is to get an idea of what you want to keep before you buy the lights. It would also help if you have a placement location. Neither are critical but coral type and tank placement can sort of help guide which light to purchase or if you want to go the DIY route. The reason why I suggest this is because not all lights are the same with regards to the lens they use, or spread, and you will compensate by height. Height of course will impact the par. MH, T5, LED, combo, etc.
Like I mentioned I have a 30" tall tank - total gallon is about 210 so a 54" W x 30" T x 30" D. I went DIY route and using a wide angle reflector which helps punch through the water. I've seen 300 par at the top and 75 - 100 par at the sand at 80% intensity. If I was to do something off the shelf I would probably consider the Kessil. Especially the new model which seems to have a better lens and form factor thus limiting the light splash. I personally want the light kept in the tank not pushing through hitting the wall, floor, etc.
TL;DR - look for lights that have a lens to focus light and punch through. Wider lens can spread and provide topographical spread.
Edit: Forgot to add. Get the manufactures coverage or light foot print. Use that to then see how much 1 light would cover.
