What is polarized light?
Polarization of Light
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The spots seen on rear windows when wearing polarized sunglasses are the stress marks of the plastic layer in between the two layers of glass in this safety glass. The spots, created during the manufacturing of the glass, act like polarizing filters and therefore block some of the light, creating small, circular, dark regions in the otherwise transparent glass.
Light is an electromagnetic wave that consists of an oscillating electric field and an oscillating magnetic field. The two fields are perpendicular to each other. In most cases the direction of the electric field has no preferred direction because different parts of the source produce light with electric fields in different directions. Such light is unpolarized. Some sources, however, like laser pointers, emit light whose electric field is always in one direction. Such light is called polarized.