Question

What are the physics principles involved in making a pair of polarized sunglasses?

Answer 1

When light reflects from water, asphalt, or other nonmetallic surfaces, it becomes polarized—that is, the reflected light is usually vibrating more in one direction than others. Polarizing sunglasses reduce this reflection, known as glare, but only when the polarizing lenses are oriented properly.

The lightbulb produces unpolarized light—each photon is vibrating in its own different direction.

Nonmetallic surfaces, such as black plastic, tend to reflect light that is vibrating parallel to the surface and transmit or absorb light vibrating in all other directions. If the black plastic is horizontal, then it reflects light that is vibrating horizontally, creating horizontally polarized light. The horizontal black plastic reflects less light that is vibrating vertically.

The polarizer lets through light vibrating in one direction and absorbs light vibrating in all other directions. When the black surface is horizontal, the reflection looks dimmest when you hold the filter so it lets through just vertically vibrating light. The reflection looks brightest when you hold the filter so it lets through just horizontally vibrating light.

Horizontal surfaces in the environment, such as the asphalt of a street or the surface of a lake, reflect light that is vibrating horizontally. Polarizing sunglasses absorb this horizontally oriented glare. If you tilt your head sideways, this horizontally oriented glare passes through the glasses, making the surface look brighter