Modern day lofts are closed in, doors close flush and most have glazed windows. When darkening lofts down you invariably have to stop light coming in through the vents to get the desired effect, by doing this you’ll no doubt interfere with the ventilation. If you find by stopping light entering the lofts and you've also restricting the amount of air entering/exiting at the same time the best way to get the equilibrium right is to keep less pigeons.