Polarization

Linear polarization

A single "ray" of light has a particular polarization direction, perpendicular to direction of propagation.

Ordinary light usually is polarized equally in all directions.

A polarizing filter allows only light polarized a certain direction to pass through.

With 2 polarizers, we can either allow light to pass through, or block all the light.
(Where "all" = 90+%)

Put one filter on a projector, second in glasses.

Problem: tilting one's head affects filtering and hurts stereo.

Circular Polarization

Combining a linear polarizer and a quarter-wave retarder produces circular polarization.

Circular polarization can be left-handed or right-handed (clockwise or counterclockwise).

Circular polarization is immune to the "head-tilt problem".

General problems:

• Many projection screen materials de-polarize light.
  
  
• Mirrors can also de-polarize light, at larger angles of reflection.
  
  
• LCD projectors polarize light internally (green one way, red & blue another way)