Is this one grill or two? Do I need one for each side of the wall?
My goal is air movement from one room to another w/no light transfer.
I cut a hole in a door and fitted it into one side, then taped up the edges on the other side of the door, so I only needed one. You probably only need one if you are ok with having the interior of the wall exposed inside your darkroom (like an open hole in the wall) -- otherwise, get one for each side of the wall but don't expect a ton of airflow (in my opinion). I wish I had installed a fan in the wall, sucking fresh air into the darkroom rather than just a louver.