Light cant bend around corners -only reflect. Get you some ducting elbows and paint those black on the inside, then assemble the bends you need with the elbows(minimum of 2 90* turns) to keep the light from reflecting. There are ways of making light boxes to keep this from happening. I made something similar in my veg room. I share the air/environment with my flower room but need to keep my flower room light proof so I made a 4" dryer vent stack "space saver" and painted the insides flat black. It looks similar to a periscope with an inlet & an outlet. I'll post some pics in a bit when lights come on. As for the cheap foil type ducting....it has a million micro pin holes in it. It isnt 100% light proof to begin with even when proper bends are made.