With them only being 15" wide, you would have to raise them up pretty good to get one to cover the entire tank. Problem with this is you will loose PAR.
Softies and LPS will do just fine with 1 unit (obviously your outer edges will be much weaker with light). SPS will do ok +/- as long as you center it under light and have higher up in the tank.
+1 on the 2 lights. You will need one light for each 24inches of tank length. If you have any concerns about the ability to grow coral check out my build thread.
You can get away with one. I had a 120W over my 75 gallon and the corals did ok. They didnt really grow fast, but slowly, they did. Just know that it is better to go with 2, but you can get by with one.
I have the older versions over my tank if you ever want to come check out my tank in Loveland. I can recommend a specific eBay seller who has had great customer service and repairs bad units in the US, so no shipping to china if one fails.
With them only being 15" wide, you would have to raise them up pretty good to get one to cover the entire tank. Problem with this is you will loose PAR.
I have the older versions over my tank if you ever want to come check out my tank in Loveland. I can recommend a specific eBay seller who has had great customer service and repairs bad units in the US, so no shipping to china if one fails.