Polarized sunglasses have a filter that blocks intense, horizontally polarized light, which causes glare. Polarized lenses are useful for outdoor sports because they reduce glare and make it easier to see clearly. However, seeing glare is desirable when downhill skiing because glare off ice patches warns skiers of the danger.
Although the filter blocks glare, the filter sometimes makes it difficult to see certain screens such as instrument panels in boats. People wearing polarized sunglasses need to make sure that the lenses do not interfere with visibility of critical instruments. Polarized lenses are available as bifocals as well as in photochromic lenses, which are lenses that change tint depending on the amount of ambient light.