yup under you mean 12 hours of light a day is plenty for a plant just as long as the humity is right and temp and ovcourse and your soil is moist
more light hrs help build strong root system thats y ppl go 18/6 and than 12/12 in flower cause thier root system should be very strong by than to hold all that heavy bud ;P
u need a grow room for 18.6 and keep them in a place for the same so the hum stays the same and gets no stress what so whever i got my veg under 64 watts sunlight works great and then flower under 430 watts hps