Moving air but blocking light? Venting two rooms together..

I need to get air through a 4 inch circular hole cut in a wall. I have a little 4 inch inline fan and flexible ducting.

Am having a goofy time finding the right material to knock down the light but that still will let the fan breathe..?

A simple bend (rigid)
And non reflective material is what I've done.
Like a periscope

Easy to make.
Good materials.. Black spray paint. Cardboard yoga pants
guerilla and electrical tape

Or idk

I use black air conditioner filter replacement foam on an upside down "U" bend semi rigid duct like said above through the shared wall between my flower and veg rooms. The ac is in the veg room window.

In the summer to help with flow I add an intake fan to one of the ducts. And 2 or 3 layers of black foam usually is lightproof with the ends near the floor with the cool air.

You can buy insulated flex piping at any HVAC supply store and yup put a loop in it

While the site was down I did exactly what you all said. Just cutting the ducting long enough to have a bend it did the trick. Covered the intake with panty hose I had from making worm tea and not because I have ladies panty hose. Usually.

Thanks all.