Hudson88 is correct in that younger plants need to be farther away from the light. If new clones are exposed to an HPS system at close distance shortly after just being under flourecents without an adjustment period it could prove fatal. You should ween your plants gradually up to the larger light by increasing the distance over the course of a week or two. Once they are adjusted it doesn't really matter their size.

A good easy test is described as follows: Cup your hand over the limb of the plant closest to the light. (This must be done after the adjustment period). If it feels comfortable for you to hold still for at least 30 seconds to a minute then it should be considered safe for your plants. If not burning but uncomfortable, then just increase the distance an inch or two and check again.

Hope this helps and good luck. Keep up with their progress!

TGT
Tom Green Thumb Reviewed by Tom Green Thumb on . LIGHT DISTANCE FROM PLANTS (PICS) how far do i keep 2 1000w MH lights from my plants? Rating: 5