or you could build a cheap box to house the grow in with ventilation and then not worry about light getting out because it wouldn't leave your box...
my grow chamber right now is made of two rubbermaid containers flipped onto each other with the lights and exhaust fan in the top container and...
I'm pretty sure that everyone here might be wrong...
That looks exactly like a pool filter we used to have at my old house... I'd almost bet my grow on it being that type of filter...
Searched "Pool Filters" in google :