Yesterday and last night we tested more films for the projection screen facing Hennepin Ave. There were several candidates. One from a Kimoto a japanese company, a 3M film, a standard rear projection fabric by Da-Lite as well as their Holo Screen and a version of their standard fabric applied to plexiglass.
The 3M film is not an optical film just a vinyl film meant to simulate frosting. Surprisingly in combination with the frosting that is already on the glass we get pretty good light dispersion. There are still hotspots on this during the day but they are not bad. This solution has the advantage of being cheap, fast to install and less obtrusive to the curtain wall because it adheres directly to the glass. It also comes in a variety of colors and opacities so we can better match the color of the glass.
The Kimoto film looked very bright. It dispersed the light better than the 3M film but not as good as the Da-Lite screens. Being a film that could be applied to the film this has most of the same advantages of the 3M film. Unfortunately they can not manufacture this in a 6ft width so our window would have seams in it; also this manufacturer is in Japan and not is not carried by anyone locally so it would take at least a week for delivery. There are still hotspots in this film but they are not very noticable.
The 3 Da-Lite screens are manufactured to be used for rear projection. The heavy gray screen gave us the sharpest picture and the greatest viewing angle. It was also had the best viewing angle during the day with a lot of ambient light. As a product of its light dispersion it actually looked the dimmest. The Da-Lite rep said they have a fabric that would be twice as bright with a smaller viewing angle. The brighter fabric would have the same physical properties (ie opaque and gray) as the fabric we have now. The sample of the rear projection fabric on plexi has the same light dispersion properties as the heavy gray screen but in a rigid application. The Holo Screen is the most transparent screen during the day. It disperses the light well at night and has a high light gain. It does not perform well when projecting on it during the day and it does not read very well from the inside at night. It could be used in a rigid application with plexi. It also has the disadvantage of being by far the most expensive and taking the longest to order (about 5 weeks).
And here are some photos: