Run Intake when lights off?

Simple question - Is it necessary to run ventilation during lights-out if there's no heat issue? I'm guessing no since photosynthesis isn't happening.

If it makes a difference, I'm using a 400w cab with a 6 foot footprint, using a 170cfm fan (it's so loud!!).

It never hurts since more fresh air = better carbon exchange. If your not using CO2, IMO it make sense to keep fresh air entering the cab, even during lights out.

CK