Heating

please help!!!

just finished my 2nd grow and my yeild is half from my first one. everything is the same apart from the temps.
I now have an air cooled light and i think the temp at night is gettin to cold about 6-9 degrees would this cause low yeilds???

thanks

It is great to have a 10 degree drop in temp at night, it helps promote nice dense nugs during flowering.