page_title: Polarization
section_title: Polarization filter
hierarchical_section_title: Polarization / Light / Polarization filter
context_page_description: Polarization is a property of some types of waves. Some waves have motion in another direction as well as the direction of the wave. In water, for instance, the wave will move across the water, but the wave will also move water up and down on the surface. Light waves are similarly transverse waves though they are also particles. Sound waves do not have polarization, since they are longitudinal waves.
context_section_description: Polarization of light is useful, after it has been filtered. A filter will separate light with one type of polarization from other types. Most daylight, or light from a light bulb, has a mix of polarizations (lasers are an exception). The filter works much like trying to put a playing card through a comb - only if the card is turned the right direction will it fit. Light that is turned a different way will be blocked by the filter. Liquid crystal displays (LCDs) use this to block light to make letters or numbers on a display. Glasses that have different polarization filters for each eye can separate light meant for the left eye and for the right eye. This is a common way to make 3D movies and 3D television.
  In nature sometimes light that bounces off of a surface has the same polarization - this is called 'glare' from a window or water. A polarization filter on a camera will remove this glare to help see through the window or water (or can increase the glare, depending on how it is turned).
  The photograph on the right was taken through polarizing sunglasses and through the rear window of a car. Light from the sky is reflected by the windshield of the other car at an angle, making it mostly horizontally polarized. The rear window is made of tempered glass. Stress from heat treatment of the glass alters the polarization of light passing through it, like a wave plate. Without this effect, the sunglasses would block the horizontally polarized light reflected from the other car's window. The stress in the rear window, however, changes some of the horizontally polarized light into vertically polarized light that can pass through the glasses. As a result, the regular pattern of the heat treatment becomes visible.
caption: Polarizing sunglasses reveal stress in car window (see text for explanation.)
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