I've had cold growing situations - it's not good for plants, especially very young ones. Get a heating pad and put it on a timer to go off once or twice an hour, or more frequently when your lights are off. (You have to get the kind of timer that has the click down tabs in 15 minute increments) Hang the heating pad vertically (with clothes pins) to keep the foliage and soil surface warm. It really helps. You will have to fiddle with it to get it just right for your situation.

Do not put pad where it will get wet!