Light usually scatters in all directions; but when it's reflected from flat surfaces, it tends to become polarized — meaning it travels in a more uniform (usually horizontal) direction. This creates an annoying and sometimes dangerous intensity of reflected light that causes glare and reduces visibility.
Polarized sunglasses reduce glare reflected off of roads, bodies of water, snow, and other horizontal surfaces.
Polarized sunglasses provide superior glare protection — especially on the water.
Polarized lenses contain a special filter that blocks this type of intense reflected light, reducing glare.
Though polarized sunglasses improve comfort and visibility, you will encounter some instances when these lenses may not be advisable. One example is downhill skiing, where you don't want to block light reflecting off icy patches because this alerts skiers to hazards they are approaching.In addition, polarized lenses may reduce the visibility of images produced by liquid crystal displays (LCDs) or light-emitting diode displays (LEDs) found on the dashboards of some cars or in other places such as the digital screens on automatic teller machines and self-service gas pumps.
With polarized lenses, you also may be unable to see your cell phone or GPS device.