We use polaroid sunglasses to minimise glare. When light is reflected from a bright non-metallic surface, it suffers partial plane polarisation. This means that more of the reflected light is vibrating in one plane than the other. For example, if you look at the morning sun reflected from a lake’s surface the light waves that vibrate parallel to lake’s surface have larger amplitude than the reflected wave that vibrate perpendicular to it. Therefore if you look at the surface of the water from an angle close to the horizontal you get more light that is reflected off the surface than light that comes out of the water by refraction. You therefore cannot see what is under the surface, just a bright flash.

To reduce the glare of this light and to view objects under the surface more clearly we can wear polaroid sunglasses. These contain polaroid cores with transmission axes that are oriented vertically so the glasses absorb the horizontally polarised light and as the glare is composed of that orientation of light they therefore reduce the glare. But they are not recommended for safe viewing of sun during a solar eclipse because they do not block out the damaging rays. They just cut down the glare. Fishermen wear polaroid glasses to eliminate reflected glare from the surface of a lake or stream and they can therefore see beneath the water more clearly. Photographers sometimes use polaroid sheets in front of lens to reduce the glare of light reflected from a surface.

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