Everywhere you go, light is reflected from every surface. Some surfaces reflect light better than others, which can become a problem when you need to see clearly. Wet roads, fallen snow, windows, and hot road surfaces can all reflect sunlight. This light is bounced off in all directions and can appear as harshly bright glare. The effect is also visible when the sun itself is directly in view. This is extremely dangerous when driving. Not only is it distracting, it can cause eye irritation and worse still, the glare can distort your vision.
Sunglasses reduce glare which makes for safer, more comfortable vision. Certain coloured tints, such as yellow and brown lenses, improve the contrast between light and shadows, which can help to alleviate these problems and improve vision.
Polarised sunglasses however, use horizontal polarisation to eliminate horizontal light waves - the type and wavelengths of light that causes glare. These lenses are therefore especially effective at heavily reducing glare especially when driving - not only during the day in the sun, but also at night under the artificial street lighting.