I like keeping mine about 3" inches or so , just because I have had the plants grow into the lights and burn my plants If I moev them too close. Also some fan leaves on my sativa plant likes to grow into the cfl's so I have to keep them about 6" away from her fan leaves to keep her from trying to touch it. Its amazing how quick my sativa plant can move looking for light If i take her out her grow box while I am doing things to the plant she will bend the top of herself toward the grow box in less than 30 minutes. My indicas dont do that for some reason.