As with any light, as close as you can get it without burning. This depends in part on strain hardiness, ambient humidity, watering schedule, and temps, but generally within 2-3" is the right distance.
stinkyattic Reviewed by stinkyattic on . fluorescent lights Instead of using those corkscrew CFLs can I use something like an 18inch or 24inch fluorescent light to give seedlings light? What if I don't want to get a sodium pressure light, what happens if you use one of these fluorescent lights while it buds? I know less yield, but what else? See attached image Rating: 5