I asked a similar question years ago and didn't really receive a good answer. IN the years since, I've done it both ways through numerous setups and it really doesn't seem to matter one way or another. Now I turn the fans off with the HPS.
thanks for the info, i did it on my last harvest and they seemed to be just fine i left the fresh air blower on and turned the extractor off. anyone else have any suggestions like is it vital to extract the air during night cycle for growth or should it be on to avoid mold etc?
If you're flowering with a big light and will get thick buds in the last weeks of flwoer, mayber then it would be a good idea to run it in the off hours, to prevent any kind of air stagnation around big, moist colas.
yes just make sure you dont have a moisture problem. I have a little clip fan that runs 24/7 but the extractor and ocilating fan run only when the lights are on.