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Polarized Sunglasses

Polarization is a process by which the direction and orientation of light waves changes on account of refection, scattering and refraction of light. It causes unwanted effect such as glare and distorts vision. Glare from surfaces such as snow, concrete, water etc curb the ability of the viewer to correctly observe object details. This can be easily observed when we observe water in a lake. The light waves incident on the surface of the water are polarized due to which we are not easily able to observe details of objects underwater.

Polarized sunglasses use filters to selectively block polarized light which is aligned in ways that obstruct vision. A polarized filter can be likened akin to an opaque sheet with slots in it at regular angles. The light waves striking this surface are aligned in all directions. The opaque nature of the sheet does not allow any other light to pass other than that which is aligned with the slots. All other light waves which are not aligned with the slots are blocked or reflected back. Polarized filters in lenses are implemented by coating a special chemical film on the plastic or glass surface of the lens. The coating normally is comprised of molecules which align parallel to each other. This can be likened to the opaque and it functions much in the same way as the opaque sheet described above.

Most of the glare encountered in day to day life comes from horizontal polarization. When light waves strike surfaces such as snow, concrete or water the polarized waves match the angle of the surface. Thus the polarized lenses used in sunglasses are in actuality vertical polarized filter i.e. they allow only vertically polarized light to enter. Polarized sunglasses do decrease the intensity of light they allow to pass through because of losses in the chemical film used. Thus the viewed surface would be darker but sharper. They find use in water sports and fishing as they reduce glare and thus help in getting a better view of objects underwater. Polarized sunglasses also find application during driving in the day. The light which is reflected off the car in front is usually horizontally polarized because the sun will be approximately perpendicular to reflecting surfaces. Thus the filter of the sunglasses would assist in reducing the glare and ensuring a more comfortable ride.