Re: polarized light sources

Interesting enough, a number of years ago I was directing in television. We bought a couple of the Rosco polarized sheets that Mark referred to. We trimmed and mounted one of them into a blank circular baby fresnel scrim frame, built a motor driven bracket to hold and rotate the polarizer in front of a baby and with it back-lit a regional weather map that was drawn on a 4'x5' sheet of ground glass. We then randomly cut out weather symbols from the other Rosco sheet.
When the weather person placed the symbols (with double-faced tape) onto the map they randomly blinked and no one could figure out how we made the little symbols blink. Kind'a fun for those days.