You would need two fixtures to cover the 48 inches I would believe. I had one radion gen 2 over my tank 36 inch length and it covered it well but I would think two in your case is necessary. As far as difference thereis a lot of difference. For one I guarantee you a radion is far far far brighter than whatever T5 fixture you have. But just some general differences the radions are completely controllable, more energy efficient, there's no changing bulbs every year like with T5's or MH, there's no heat transfer, IMO LED's are better than any previous form of lighting in just about every way possible. Now I stated IN MY OPINION because there's lots of debate. Some people have preferences, some people have a "if it ain't broke don't fix it" mentality meaning they like their T5's and halides so why change it. Some people don't think LED is proven enough so aren't fully convinced enough. As for me I'm convinced. LED's are fantastic. If you can get past the sticker shock for a radion or even other LED fixtures they are worth every penny. But even if you think LED's are too expensive you can go used or there's great other fixtures for less for example Reef Breeders are great, Rapid makes nice fixtures as well. So yes I'd say if you can afford it go LED.