I can't get T5 bulbs in the four foot length at my local big box store, so for me T8 flourescent shop lights are the most economical. T5 means the bulb is 5/8 ths of an inch across. These bulbs are very flexible for a glass tube. T8 is a bulb 8/8 ths of an inch across or a one inch thick bulb. Both T5 and T8 use electronic ballasts. T12 flourescent bulbs ate 12/8ths of an inch thick or 11/2 inches, and use the old style ballast instead of electric. They are the cheapest to buy but the more expensive to run. Check the box stores in your area to see if they carry T5 or T8. I've been using the fixtures with two bulbs per fixture. If you want to increase the light, you may want to go with a four bulb fixture.