For veg you want 24"-30"
For flower you want it closer to 18"
I'm a total newbie but I own a vipar spectra 600w reflector series as well. I started my clones under a 315w cmh but moved them to the led once I transplanted them. I noticed that my plants (which I just transplanted into 2 gal cloth pots) are starting to yellow a bit. After reading what you suggested tags420, I moved my led up to 24" and gave them a good feed through 2 days ago, I had been going too light on the fertilizer, I think, but with the last feed through I used the recommended amount. I'm using medi-1 fertilizer and coconut soil. My questions are; is my light too close and thats whats causing the yellowing (one leaf is even curling up a bit, little brown on the tip)? And the next question is; how often should I be feeding them, they're about 8-10" tall but not filling out lower on the stem. I'm getting all kinds of different advice, feed feed water/feed feed feed feed water, or with coconut soil the guy at the garden center said I could water and feed more frequently than that and way more than regular soil. I'm worried about over feeding, so the next question is how can I tell if I'm feeding too much or too little? Or should I just give them a light feeding with fertilizer at full strength a few times then a water through (watering or feeding until it soaks thru the whole pot/plant roots)? I never had a problem with my cmh, but its too hot to run in my apartment, so thats one of the reasons I switched to the led. Help?