I had some kind of plastic based transparent material that I was taken from my unlucky lcd tv. The mission of this material was homogenizing the light imo. Because it was placed between the lcd screen and cold cathode flourescent bulbs (in my ..... tv).
Anyway, I put this homogenetic lol material onto my cheap(-est) curtain and shocked with the results

. As you could see that on the picture; brightness & color temp. was dramatically increased. It also provides much better "black" than usual projection screen...

You can see its transparency level in this photo.

I'm not sure where to find this material, but I think it can be found in decoration stores (or somethin' like that lol).