I just got a 4 bulb 4 foot shop light for T8s. I intend to set my timer for 14-16 hr on and 8-10 hours off. I also intend to pay close attention to keeping the tubes as close as possible to the seedlings. It does depend on what you are going to be growing. Different types of plants can be real fussy in different ways. Mostly that will be for a few tomatoes, some peppers, some broccoli and some cabbage. (I might also cheat on some sweet potatoes.)