Lightproofing ventilation

Looikng to make a light trap/stop light leaks from a 12' max fan with the least amount of cfm loss possible..

The fan is between two flower rooms, sharing an ac.

I looked into dust shrooms but they are pretty expensive, but that might be the best route.
I would definitely need two, because I looked at one and it didn't quite do the trick...


Dark room vents seem like they would cut down on flow quite a bit....


Also can anyone can interpret this chart from can fans site? I am not sure what "wg" stands for?
Is it "static pressure" or inches of ducting or something like that?

Performance Data
|--------------------------- in. wg -----------------------------------------------------------|
-----------0" -- .125" .25" .375" -.5"* .75"* 1.0" -1.25" 1.5"
CFM 8" - 667 --650 --630 -610 -585 -520 --420 - 150 -100
CFM 12" 1708 1680 1655 1630 1595 1530 1460 1380 1300
 
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