T8 vs. T12

I am growing a few plants right now and i have a 4 foot shoplight fixture with both T8 and T12 bulbs. I was wondering what type of bulb is better off for the plants? to me i think the T8's are brighter.

the smaller the number the brighter the bulb.

a t8 bulb in a t12 fixture will burn the ballast up.

and yes the t8s have more lumens / less watts

thanks for the reply's...appreciate it