Why do I need a special 3D screen?

The images intended for the right and left image channel are projected simultaneously on the screen. Due to the polarization filters in front of the beamers, the direction of the polarization differs for each of the both image channels. A traditional white screen reflects the impinging light in an unpolarized way. You would see both image channels with both eyes. The effect is similar to when taking off the 3D glasses in a 3D cinema.

A silver-coated 3D screen reflects impinging light while maintaining its polarization and the viewer sees the two image channels separately when wearing 3D glasses. In reality, the so-called silver screen is uniformly coated with a special aluminum color.

Polarization conserving films and plates fulfill a similar function in 3D rear projections.