I use normal CFLs on a 16 hours a day timer. I have two Acer Buergerianum seedlings, 7 Syzygium australe seedlings; one Polygala myrtifolia seedling and a two-year-old Ficus Natalensis I hope will grow over a beautiful rock.
Manofthetrees is correct that you should keep an eye on the colour temperature of the light that you use. I am currently using a 11W Cool white(4000K) (only one I had in the house), but my trees get a little bit of sunlight trough the window (1Hr in the summer, 3hr in the winter).
I would however recommend using a combined total of around 40W of florescent lights for best results. Then you wont necessarily have to give them 16 hours of light a day, like me. My trees grow very well with CFLs, but I do take care not to shock them with a sudden change, i.e. from lots of sunlight to CFLs. My big trees are however outside. I will keep them all in the tank until after winter (around August). The Natalensis I am planning to leave in the tank, and maybe the Polygala myrtifolia, its growing like there is no tomorrow.