It all depends on penetration. You could probably keep sps 12"-16" from the light. I have a 30 gallon with some sps on the tops of my rocks. They are doing well about 3"-5" below the surface and I have my 4x24 watt light mounted about 10-12" from the surface. You wouldn't be able to keep a full blown sps set up with it if thats what your asking.
I had a 4 bulb t5 fixture over a 55g (23" deep) and I was able to keep easy sps and a clam on the bottom, more difficult sps up on the rocks. A 6 bulb fixture would be better, but if a 4 is all you have, it can work.
Yeah the 4 bulb fixture is what I have right now. I just bought this set up and promised the woman that I would sell it and make some money, but, I ended up Decided that I'm going to set up another tank up in my house. ;-) I'm all led on my other reefs but figured I'd try the t5 until I can order something else
You will be able to keep some sps but its gonna have to be high up and directly under the bulbs. A 6 bulb would work way better but you should be ok for now as long as its not alot of sps lower in tank.