Light, like radio transmissions and nuclear radiation, is emitted in the form of electromagnetic waves. Specifically, light travels in transverse waves--that is, while traveling along a generally straight path, light waves will vibrate in many directions perpendicular to that path. However, there are several methods available to filter light, causing it to vibrate in only one plane perpendicular to the path of travel. Such filtered light is called polarized light.

When an electron is excited it will vibrate; if excited further, it will sometimes emit a photon of light. Since the excited electron vibrates in only one direction, that photon will also vibrate along a single plane and, therefore, be polarized. If all electrons in a material vibrated in the same direction, all the light emitted would be plane-polarized. In reality, though, the material's electrons vibrate in an almost infinite number of directions, producing...