Polarisation by reflection

When white light illuminates the surface of a transparent material, the electric fields of the waves interact with the surface molecules, giving rise to partial polarisation of the light.

The reflected and refracted waves come from a single beam of unpolarised light, so if the reflected wave is partially polarised in one direction, the refracted wave is also partially polarised in a way

which complements it. (If the two were to be rejoined, the resulting light would be unpolarised.)

Sunglasses reduce glare

Polarising filters are used in sunglasses. Sunlight reflected from smooth horizontal surfaces such as water is strongly polarised in the horizontal plane. Sunglasses are worn with the polarising axis of the lenses vertical and much of the horizontal component of the light is absorbed, significantly reducing glare.

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