I purchased a doran fan and 2 louvers recently and installed them in my darkroom.

I've printed about 4 or 5 times over the last two weeks and always at night.

I went in today during the afternoon and found light pouring in thru the supposedly light-tight louver.

Any hints? Did I install it wrong (I did follow the instructions). Can I fix the louver? The one on the fan is perfect.

Just modify the discharge side.

Put duct work on it pointing down, or build a box around it with the opening on the bottom...

or if it needs to point straight out make a box around it as wide as need be about 12-18 inches deep and put a woman's black headscarf over the opening -- like shooting glamour on a sunny afternoon. ;)

When I've mounted vents on a hollow wall I've always offset the louvers from each other by as much distance as the wall will allow and not be on the floor to gather dust. Spray black paint inside the holes as far as you can from both ends and you will find very little light can make it around the corners you've built.