Polarized sunglasses reduce glare by blocking light waves vibrating in one particular direction.

The longer version

Light scattered from a flat surface such as water or a road becomes partly polarized, with its waves vibrating mostly in one plane. A filter whose molecules are aligned in a fixed direction absorbs waves oscillating along that axis and transmits the rest, cutting the glare.

The idea came from nineteenth-century work on polarized light, and the same filter appears in photography to darken skies and remove reflections from glass. Two crossed filters block nearly everything, which is how they are tested. Some animals orient themselves using the polarization pattern of the sky, which human eyes cannot see without help.

Where this entry sits

These facts explore how light behaves and how human eyes turn it into the colors we see. Along the way you meet rainbows, prisms, mirrors, shadows, lasers, and optical tricks that fool our vision every day. The full list sits on the Color and Light page, where every entry is listed in order.