I let them grow a bit too high and they were touching the lights on the left side and they burned up up a little bit. Nothing to severe but definitely something to note. Once they get within an inch away from my marshydro300''s they will fry.
not too sure about my 600's my guess is 2-3 inches maybe even more. I haven't let them get that close yet, but I am running out of headroom
Checked the plants yesterday for the first time in a few days and they grew so fast that a few of the tops grew into the lights again and they got fried yet again, only about 4 of the tops so it's no biggie. I've raised the lights again and they are now and the highest setting. I might have to start bending them down if they keep stretchin