I was changing some light bulbs in a sting of three fixtures that had 20 watt two foot flourescent bulbs that were t12s. I couldn't get the new 20 watt bulbs to work even though there was power to them. I took the cover off and the ballast said it was for 15.2 watt lamps. I don't know how long the bulbs had been out but I guessing it won't power a 20 watt bulb and a two foot 15 watt bulb can't be had. Time to update the ballasts or fixtures as they are old would be my guess. Thanks for any help.