Put your hand above your plants and if your hand gets really warm after a min. or so then your bulb is too close. You could probably get 6-8 in. should be alright. Dont go by the color of your pistils go by trichome production. There's all kinds of factors that can make the hairs turn colors. If i were you id go to radio shack and get a 60x handheld microscope for 13 bucks. If the trichomes are clear to cloudy its a more uppity high and if they have more amber coloration its more of a couchlock high. Thats the best way to tell when your buds are ready. Hope that answers your question.