I have a 600w HPS that i switched my 6 seedlings over to a day ago. I started it at about 32" away, the next day it seemed like the plant on the outside leaned a little, so i lowered it to about 28", and now i just lowered it to about 2' away. The temps at plant level are right around 76-81*. Using a 450cfm exhaust w/ carbon scrubber and a 250cfm passive intake. I have a small oscillating blowing on the tops of the seedlings. I'm hoping this isn't too close for these little guys. Seems to me I should be able to continually lower it until it's about a foot away, since i'm not giving them nearly as much light as the sun would Anyway, here's some pics, and the cotyledons are looking yellow already, are they supposed to be yellowing out already? It also looked like the new leaves coming in were a bit yellow but people just keep calling me paranoid They were just transplanted into FFOF a day ago also. The first one seems to be curling under quite a bit, but I've been told it looks fine and healthy... Oh, i've also kept light on them for 24/0 so far. I think tomorrow, since they are now under the HPS, i'll switch to an 18/6 schedule.
They look ok. That's not too close but don't move it any closer until they grow more. Here is a useful chart to help you gague light intensity in this other thread: http://forum.grasscity.com/absolute-beginners/305883-please-help-lighting-issues.html