Blocking Light out

I’m trying to block some light from coming in my room with my 8” ducted fan. Is there any design available so no light leaks in? Thanks

If it’s entering thru the ducting, bend an S shape in the ducting. Or even a 180° bend should stop it.

I bought some 90s and straight connectors. Painted the inside of them in flat black. Stopped the light dead. Took my inline fan out and painted it too inside.