It's not so much the lighting, but the root warmth, esp. in outdoor space- greenhouse, bldg. I live @ 35.6 Lat. . My girls did well until temps dipped under 28F at night. Moved them inside to finish. Getting 14-15 hrs of sunlight, plants still grew nicely being in the warm zone during the day. Used Wall-o-water tube shrouds to keep heat in at night or dark plastic bottles (1.5 qt) to heat during the day, dissapate at night. Started in April outside w/ Wall-o-Water...no problems . Light inside (cabinet), I do 20/4...saw 20% appreciable difference than 24 on. Twenty percent is not much, but when it's in grams, yep, a difference!! Botany minor in college....plants do better if periods of light/darkness. Photos esp....I did 13.5/11.5 to flower....muy wonderful!