Polarized 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 polarization, much like a venetian blind controls sunlight through a window.

Sunlight itself is not polarized - 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. Polarized lenses have a laminated surface containing vertical stripes. These stripes only allow vertically-polarized light to enter the wearer's eyes. Glare is eliminated because the horizontally-polarized lightwaves cannot bypass the polarized filter.

Polarized lenses do not provide universal protection from glare, however. If the wearer tilts his head past 45 degrees or so, some of the horizontal light can enter and cause some bright spots. Some wearers who use polarized lenses in snowy areas may find that they lose some contrast between snow and shadows. Fishermen and drivers seem to derive the most benefit from polarized lenses because they deal with mostly horizontal surfaces. A fishermen wearing polarized sunglasses can see below the surface of the water to search for schools of fish or hidden obstacles. Drivers are no longer affected by a constant reflection of light from their hoods or the road ahead.

There are some limitations to the use of polarized lenses, however. Because the vertical polarizing stripes reduce the amount of light entering the eye, polarized lenses cannot be used for regular eyewear with clear lenses. Prescription sunglasses can be tinted a very light gray to acccomodate the polarized laminate, but most contact lenses cannot. Some drivers discover that polarized lenses can cause distortions in liquid crystal displays (LCDs). Onboard clocks and other instrument displays may be temporarily unreadable.

Both horizontally and vertically-polarized lenses are used to view three-dimensional movies. Some of the light reflected from the movie screen is vertically polarized, which means only a lens with a similar vertical laminate will receive it. The other lens only receives horizontal lightwaves. Your brain takes both of these images and combines them to create a realistic sense of depth.