Polarized sunglasses are designed to reduce the glare from surfaces like water, snow, and glass. They can be highly useful for sports, driving, and fishing by helping the participant in these activities to see more clearly, allowing for the avoidance of potential hazards. While they may be somewhat more expensive than conventional sunglasses, some consumers prefer polarized sunglasses because they selectively block out glare, rather than making the whole field of vision dimmer, which can be dangerous in some situations.
Light has many interesting properties, especially when reflected from another surface. Polarized sunglasses take advantage of one of these properties, known as polarization. Normally, a light source produces waves which go in all directions. When light is bounced from a surface like glass, water, or snow, the light waves polarize, meaning that they orient along an axis, which is usually horizontally. A vertical polarizing lens can reduce the brightness of these light waves while still allowing optical information through.
Because of their vertical polarizing orientation, these sunglasses are ideal for dealing with reflective glare conditions, depending on the angle. Experimentation with polarized sunglasses can yield an angle at which no light is filtered out, because the glasses are horizontally aligned along with the glare. At other angles, the sunglasses will filter out some or all of the glare, allowing the wearer to see with comfort and without potential eye strain. Polarized sunglasses are unfortunately not as useful when the sun is directly overhead or low to the horizon, because the angle of the reflected light waves changes from this horizontal configuration.
These sunglasses are primarily used in situations where the wearer needs to be able to clearly see, but also needs to have dangerous glare filtered out. Glare makes vision difficult because the light hurts the eye and obscures details which may be hidden behind it. Conventional sunglasses will block out glare, but they will also block out subtle details about the wearer's environment which may be dangerous. These polarized sunglasses designed for outdoor use usually come in a variety of configurations from very lightly tinted and mildly polarizing to heavily tinted and strongly polarizing. Some also integrate color tinting for visibility in specific conditions such as snow.
Some 3-D movies also use polarizing glasses. Usually one lens is horizontally polarized and the other one is vertically polarized, so that each eye sees a slightly different version of the movie screen. The eyes attempt to reconcile the two images for the brain, and the result is the illusion of a three dimensional image. Experimenters with several spare pairs of 3-D glasses lying around can play with the effects of polarization for themselves.