I t should say on the bulbs. How many bulbs are in the fixture? If I had to make a guess, it is a 110 watt fixture with 2 55watt bulbs. They are 48 inches long.
my 24" compacts are 65 watts each, total of 2 of them, so I would guess that your 48" bulbs are higher watts, more like 96 or somethin in that area. Do you still have the box they came in, it should say on that or maybe on the bulb.