Polarized lenses reduce glare by using a filter that blocks light reflected from flat surfaces or smooth water. Sunglasses that use polarized lenses are popular among boaters, fisherman and people who enjoy outdoor activities that benefit from glare reduction, such as skiing or biking.
When sunlight hits a flat surface, it becomes horizontally polarized instead of being scattered in all directions. This causes the reflection to travel in a horizontally oriented direction, which results in glare. Human sight requires light that is vertically oriented to be able to see, making polarized lenses useful because they eliminate the horizontally aligned light waves that induce discomfort and pain while allowing vertically aligned waves. Sunglasses that use polarized lenses are particularly useful when driving a car during clear weather as they reduce the bright reflections from the road and the vehicles ahead.
Expensive and higher-quality polarized lenses that are made using polycarbonate, an impact-resistant material, provide protection against ultraviolet light. This property is important because the eye allows in more ultraviolet radiation as the pupil dilates in response to the overall reduction in light.
The downside of polarized lenses is that they reduce the visibility of images and information displayed on liquid-crystal and light-emitting-diode displays, found on dashboards or automatic teller machines. GPS screens and cell phone screens are also difficult to see with these lenses. They can also prevent skiers from spotting patches of ice because they block the glare from the ice that normally reflects more light than the surrounding snow.
Lens polarization is widely available and can be used with bifocals or progressive glasses, as well as photochromic lenses.