I would use the fan and filter this way:

Filter first, then fan, then ducting thru light. You will be pushing filtered air thru your light. The cfm rating of your filter usually means max airflow. If your fan pushes more air or makes more noise than you like just add a rheostat and you can adjust airflow.
grey1223 Reviewed by grey1223 on . Questions on some products I'm trying to plan my grow room redesign coming soon after this flowering phase finishes and I was wondering if anyone has insight on the following products: Odor Sok: these are filters that are much lighter than conventional carbon scrubbers. They are made with fabric made out of virgin activated carbon as opposed to being filled with the carbon pellets. I was curious how well do these flow and how well do they filter out the odor? SolarMax 400watt MH conversion bulb: These are normal Rating: 5