PC question??

[frd72]

I have 8 X 65w retro fit PC light. Do i need to put 8 bulb or i can just put 2 or 3 on each set. It has two ballast that control 4 bulbs each?
I experiencing GFCI trip every time i plug in one set, i already changed the ballast..no short circuit what so ever in the canopy. the only thing i have right now is i'm missing some bulbs..Any response will be appreciated..

thanks,
teddy