Three dimensional (3D) sunglasses are an entertainment accessory that take advantage of our binocular vision and are able to make a specially prepared two dimensional image appear to be three dimensional. Binocular vision is the term used to describe the image resulting from two eyes being used simultaneously, as humans do. When an image or film has been prepared for use with 3D sunglasses, it is actually comprised of two images, one intended for each eye. The 3D sunglasses force each eye to see only one of the images, and the brain then combines the two, which creates the illusion of a three dimensional image "popping out" from the surface the image or film is being viewed on.
Binocular vision results in a single image being perceived as a result of binocular fusion, which is the process in which the brain takes the two slightly different perceptions of each eye and combines them. This is an useful ability that produces a wide field of view, increased depth perception, and the ability to see faint or far-away objects more easily than if the viewer had only one eye. This is the primary driving force behind the function of 3D sunglasses, which filter distinct images into each eye. Binocular fusion causes the brain to unite these images so that, while there are two images, the viewer perceives only a single picture.
There are several different ways in which 3D sunglasses accomplish the isolation of each image for each eye, but the most commonly used are dual-color lenses and polarized lenses. The lenses in dual-color 3D sunglasses are usually red and blue or red and green. The image that has been prepared for viewing shares these colors. Polarized lenses make use of light polarization, which is the process in which light waves are made to move in only one direction. Each polarized lens detects one source of light.
Images or films intended to be viewed with 3D sunglasses will have two different images that have been spaced slightly apart, either in colors that correspond to those on dual-color 3D glasses or as light patterns intended to be viewed by polarized 3D sunglasses. Polarized images are generally considered superior to dual-color images as they allow for full color to be viewed. Since dual-color 3D sunglasses use color to separate the images, the quality and richness of the color is significantly reduced.