+1 for heat stress.
If the room is hotter than hell, it doesn't matter how far way you keep the lights away from the plants.
But then you say the lower leaves are turning yellow.
That could be a deficiency or lockout. Typically Magnesium.
If MG, the best solution would be to add a tsp gallon of Epsom Salts. You'll get a little sulphur, too.
But I recommend checking your ph first, because if it is out of whack, then the yellowing is most likely a K lockout.
SO. all that said, here's the order you take to troubleshooting this prob:
--Improve the temp/condition of the room
--test/adjust ph. Wait a day to see improvements
--then you raise MG level with epsom salts, cal-mag (advanced), or sweet (by botanicare) if necessary.
Or try my nutes
