I have a grow rack that is at the south facing set of glass doors. It's actually a foot away from the glass, which is as close as I can get it. There is an eave that juts out a foot and the space between the racks is also about a foot. As the sun gets and stays high in the horizon, as it is doing now, the sun gets cut off by the eave and the proximity of the rack tiers. Therefore, I need to supplement the window light with fluorescent lighting.

I basically turn on the light and open up the blinds around 8 am and go to work. I don't get home from my job until around midnight, long after the sun has gone down, leaving the artificial lighting as their source fo light.

My question is what are the plants responding to? Do they think that they are receiving a 16 hour photoperiod? Or are they really responding to what shines through the glass doors? Are they distinguishing between winter and summer light or do they think it's perpetually summer?