here, you gotta put these in perspective......
1ft for the bucket
1ft for the actual light (if using H.I.D.)
1ft of space between light and ceiling (heat issues)
1ft AT LEAST for space between light and plants.
so just by that right there, is 4ft that you NEED without the plants being there... so really if you want a 4ft tree at harvent you need 8ft of heigth total..... Im letting mine go in veg til 24in. they MAY double or triple but I doubt that