It should say on the side of the bulb what it is like 40 watts {1 or 2 bulbs} if it's 2 bulb you would need a ballasts that has wire for 80 watts {2x 48in bulbs}, you can find those in Lowes, Home Depot or Light Stores
it's when you get into VHO, t5, HQ's an MH you will have to order the ballasts on line.