Doran DV-99 8×8″ Light Tight Darkroom Louver for D-68 and DVM-199 Fans
Each Doran Light Tight Darkroom Louver is designed to supply just the right amount of air to a particular model exhaust fan.
Note: Exhaust fans work best in a darkroom equipped with fresh air supply louvers or some other kind of air supply. If there is no air supply to the darkroom the fan will be working against a vacuum and can do nothing.