Leaves are turning upside down.

remember that if the lamp is properly ventilated you should 1) never have to open your closet door and 2) you should be able to keep ur girls as much as a foot a way from your light.

Hi,
I have the same problem.
I have 300Watts (3x100W) in 75cm² with two computer fans circulating the air. One on the top pulling air out and one on the bottom pushing air in. It can get to 40°C in there but that is only at midday.
But for some reason one of the plants, the largest, turns her fan leaves over for a few hours and does not turn them back over till the light has been off for a few hours. I am not too sure when she turns them back over because I am asleep.
It has happened twice. Once all the big fan leaves went on strike and turned over and yesterday only one turned over. Today they are all back on the job.
Not too worried about it any more, but I am just interested in know what would cause this to happen. I have never seen anything like that in nature.
It only takes the plant about 4-5min to turn the leaf 180° degrees too. I thought that was amazing.

Cheers, and happy growing