I really should think all these post though rather than just posting like 5 times in a row but wheres the fun.. i found this and a link to help you understand
"The bulbs are limited by their design to draw only so much current and no more. If you double the amount of current, you wonâ??t get a bulb thatâ??s two times brighter because the efficiency drops off a bit. So even after the increased current is made available, a bulb driven by a factor of two times its normal supply, only gets 1.7 times brighter." http://www.geocities.com/teeley2/overdrv1.html

so for my application i over drove 4 40w lights which become 68 watts which is 272w of fluros cooled with only a computer fan keeping it in check. Or 136 for every 2-light shop fixture i overdrove.. cost... 7. for the shoplight 18 for the ballast