What is Polaroid Sunglass?

Polaroids are thin and large sheets of crystalline polarising material capable of producing plane polarised beams of large cross section. In 1852, it was discovered by researchers that synthetic small needle shaped crystals of iodosulphate of quinine possess the property of polarizing light. These crystals are not stable. A polaroid sheet is prepared from the suspension of these crystals of nitrocellulose. To impart stability, its thin sheet is mounted between two sheets of glass or celluloid.

It can also be obtained by stretching a thin sheet of polyvinyl alcohol strained with iodine. When such a sheet is subjected to a large strain, the molecules get oriented in the direction of applied strain. If the Stretched sheet of polyvinyl alcohol is heated in the presence of a dehydrating agent such as hydrochloric acid, it becomes strongly stable. Each polaroid sheet is enclosed between thin glass plates so as to provide mechanical support.

Polaroids are of two types. H-polaroid and the k-polaroid. The main difference is that k-polaroid are not strained with iodine.