Polarized light reflected from an ordinary motion picture screen typically loses most of its polarization, but the loss is negligible if a silver screen or aluminized screen is used. This means that a pair of aligned DLP projectors, some polarizing filters, a silver screen, and a computer with a dual-head graphics card can be used to form a relatively high-cost (over US$10,000 in 2010) system for displaying stereoscopic 3D data simultaneously to a group of people wearing polarized glasses.
In the case of RealD a circularly polarizing liquid crystal filter which can switch polarity many times per second is placed on front of the projector lens. Only one projector is needed, as the left and right eye images are displayed alternately. Sony features a new system called RealD XLS, which shows both circularly polarized images simultaneously: A single 4K projector displays two 2K images one above the other, a special lens attachment polarizes and projects the images on top of each other.
Optical attachments can be added to traditional 35mm projectors to adapt them for projecting film in the “over-and-under” format, in which each pair of images is stacked within one frame of film. The two images are projected through different polarizers and superimposed on the screen. This is a very cost-effective way to convert a theater for 3-D as all that is needed are the attachments and a non-depolarizing screen surface, rather than a conversion to digital 3-D projection. Thomson Technicolor currently produces an adapter of this type.
When stereo images are to be presented to a single user, it is practical to construct an image combiner, using partially silvered mirrors and two image screens at right angles to one another. One image is seen directly through the angled mirror whilst the other is seen as a reflection. Polarized filters are attached to the image screens and appropriately angled filters are worn as glasses. A similar technique uses a single screen with an inverted upper image, viewed in a horizontal partial reflector, with an upright image presented below the reflector, again with appropriate polarizers.
On TV and computer screens
Polarizing techniques are easier to apply with cathode ray tube (CRT) technology than with Liquid crystal display (LCD). Ordinary LCD screens already contain polarizers for control of pixel presentation — this can interfere with these techniques.
In 2003 Keigo Iizuka discovered an inexpensive implementation of this principle on laptop computer displays using cellophane sheets.
One can construct a low cost polarized projection system by using a computer with two projectors and an aluminum foil screen. The dull side of aluminum foil is brighter than most silver screens. This was demonstrated at PhraJomGlao University, Nônthaburi, Thailand, September 2009.
Health care
In optometry and ophthalmology, polarized glasses are used for various tests of binocular depth perception (i.e. stereopsis).