light proof room to room fans?

I'm looking at room to room fans.
I was wondering if anyone knew if they were light proof or not?
I have found dark room louvers, but all of those are black and really too pricey. Anyone know of any white ones or other ones that would do the job and keep the light in check?

Thanks
~~ Flams ~~

Black box the fans simple. Paint inside of a box flat black leave two sides open. Light will not reflect from flat black.

I've thought of this and indeed will do this. but was hoping to find something pre made on this application. I want it to look sleek like the dark room louvers

Paint the louvers flat black........

Try speaker covering cloth it lets air through but not light,it also has the added bonus of acting as a air filter.

Good ideas

does speaker covering cloth really not let light through? i mean it has little holes in it, and you can see through it so how can it not let light through? not sure this works tbh, but id be happy if it could be confirmed, would be a great solution for me.