about 20-24"......lower it day by day,,,by about the second week you can have it about 10" above ya plants if you have a fan blowing over the top of um,,,12"if not ,,by about the 3rd-4th week you can get as close as 8"with a fan blowing over the tops pushing the heat away..you may get very minor stretching at first but thats very easily fixed when you repot!i started all my plants under a 400watt mh and they grew all bushy...there flowering nicely under a hps now.peace