Polarised lenses are used in sunglasses to reduce glare from reflective surfaces such as the surface of a lake or the hood of a car. They accomplish this feat through a process called polarisation, much like a venetian blind controls sunlight through a window.
Sunlight itself is not polarised – light from the sun will either be absorbed or reflected horizontally, diagonally or vertically. The problem this causes for fishermen and drivers lies in the horizontal reflectivity. Sunlight bouncing off a horizontal surface will strike the viewer’s eyes at a similar angle. This means the glare from the surface of the water or the road or the car hood will be strong. Polarised lenses have a laminated surface containing vertical stripes. These stripes only allow vertically-polarised light to enter the wearer’s eyes. Glare is eliminated because the horizontally-polarised lightwaves cannot bypass the polarised filter.