are there going to be plants in there? And what kind of lighting are you looking to get ....standard T8, T5 NO , T5 HO? A standard 36" T8 or T5 will not be very bright for a 48" tank, and it will give you dark areas on each side of the light. That's what my 48" has now since my other light just broke and it's pretty dim in there except right under the light. Also if you want a glass top J&L aquatics carries them for around $35. They also carry a Sunlight Supply Sun Blaze T5 HO Strip Light (48 Inch, 54 Watt) that would light it up quite nicely. It doesn't come with a reflector , but they sell the one for it there too. The light is $33.45 & the reflector is $18.95 plus tax. Good price for a sufficient high output light for your tank. Here's the link for the light:
Sunlight Supply Sun Blaze T5 HO Strip Light (48 Inch, 54 Watt)
and the link for the reflector:
Sunlight Supply Sunblaze Strip Light Reflector (54 Watt)