Depending on how cool the area is I would try to keep it no more than 15 inches away and a FT if temps are cool. Make sure you have a little fan blowing between the plants and the light, but remember seedlings are still pretty week and can get bent up by a fan that is too high. Once they get a little stronger then I would try to get down to about 8 inches or so. I keep a 175MH on my clones and it is about 8 inches away and sometimes they still want to strech out to grab at it.
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