I converted my 4 foot lights to ballast by pass bulbs. I bought mine from amazon, they cost me about 65$ per 10 bulbs the cost goes down if you by in bigger quantities. If you go to You tube look up Chris Notap he does a demo and gives part numbers. You might not need new tombstones ( bulb holders ) take one fixture apart and look at how it is wired. My bulbs are 5k lumens daylight. They work at sub zero temps. Love em.