Slightly off-topic, but the light from the LCD projectors is polarized.
I particular, the projector in my classroom polarizes green light one
way and blue & red rotated 90 degree from that.
This can make for some fun demos. Show how colored filters will cast
shadows of the same color. Then show that a "gray" filter casts as
green shadow. As everyone is puzzling over that, pull the polarizer
back and subtly turn it 90 degrees and try again.
It also works very well to show color addition of the projectors -- red
and green make yellow.