T-5 high output fluorescents (thinnest tubes) are hotter than you would think. A lot depends on the size of your closet. The more area to dissipate the heat, the less heat issues you have...to a point.

I don't know anything about T-8s but T-12s (the old standard fattest tubes) can be used in some low light situations, like seed sprouting, cloning or keeping mothers. However, they are pretty inefficient for the light they put out. And more importantly, you won't be able to bloom well, if at all.

If you have a small area, consider using CFLs, although I have no personal experience with them. You would have to do your research.

In almost all circumstances, you have to have ventilation to bring in fresh air/CO2 and remove heat buildup.

Even if you can't do a site search, you can go into the grow forums and read the stickies and some of the highest rated threads.