Light consists of photons which have the characteristics of both particles and waves. Photons emitted from the sun as well as from artificial light vibrate and radiate in all directions. However, when light is reflected from certain flat surfaces it tends to travel in a more uniform direction – usually horizontal such as from a lake, a road or other horizontal surface.  This is “polarization” – when reflected light is more intense in one direction. This intensity of reflected light in one direction causes glare and reduces visibility.

Normal sunglasses use tint to reduce the brightness of light from both vertical and horizontal light.  Polarized sunglasses lenses contain a special filter that blocks this type of intense reflected light, reducing glare.

Because most of the glare that causes you to wear sunglasses comes from horizontal surfaces polarized lenses in sunglasses are fixed at an angle that only allows vertically polarized light to enter. Here’s a diagram:

A drawback is that polarized lenses may reduce the visibility of images you want to see such as your cell phone, tablet or other LED or LCD displays.