I've seen okay results with T-12s, but you need a lot of them. What's cool about T-12s is that they put off zero heat on the tube itself. The only hot parts are at the two ends of the bulb. That means you can have plants touching the light without any damage. Negatives of using T-12s is that light penetration/intensity sucks. You'd be better off with CFLs, T-5s, or T-8s.