Stewart has two styles of perforated screens. One for typically used in commercial theaters and the THX rated "micro perf". The hole diameters in the micro perf are considerably smaller.
The actual light loss from a Stewart THX micro perf will run between 8% and 9%. The human eye, however, cannot perceive a change in light intensity of less than 10%. Thus, while there would be a measureable decrease in the reflected light from the screen, you could not perceive that difference.
The THX microperf is available on all the screen materials used in their screens (except rear projection). This includes the Studio Tek, Ultramatte, Video Matte, and Silver 3D. The MicroPerf process does not cause a color shift, increase hot spotting or change off axis characteristics of the screen.
This is also true of the Cine Perf (more commonly found in commercial and military applications).
The MicroPerf are used in the screening rooms at Skywalker Ranch.
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[This message has been edited by Dennis Erskine (edited July 18, 2000).]