If you aren't already doing it, try staggering the bars for more even lighting. Solaroasis recomends a single 60 watt bulb (they didn't specify what kind but I am assuming incandescent) for increased infrared light which is beneficial to tomatoes and I would assume cannabis, it would probably raise your temperatures as well. Temps lower than 60 F will slow growth, try and aim for low to mid 70's.