Two sides plus red and green light gives full color illusion.

Two slides plus red and green light gives full color illusion. Note: Projectors should be level so there is no keystoning. A still-life scene has been photographed twice on black and white slide film, first through a red filter, and then through a green filter. The first slide plus red filter is inserted in projector 1. The second slide plus green filter is inserted in projector 2. When both projectors are turned on, and the two images are superimposed via a beam-splitter, the image that appears on the screen gives the illusion of being a full color rendition of the still-life scene even though much of the spectrum is missing. The variac controls the light intensity of the green projector. References: Scientific American, E.H. Land, May 1959, pg.84 and Scientific American, E.H. Land, Dec 1977