Polarized Light, light in which individual light waves are aligned parallel to one another. The fact that light can be polarized shows that it is made up of transverse waves, because only transverse waves can be polarized.
Light may be polarized partially or completely. Light is polarized when it is reflected from a transparent material, such as glass. The degree of polarization depends on the material and on the angle at which the light is reflected. In the sky, light is polarized by being scattered by particles suspended in the atmosphere. When light is passed through certain crystals, such as Iceland spar, it is split into two polarized beams. When a beam of light is passed through certain other materials, such as tourmaline or Polaroid plastic, one polarized beam emerges. All materials that polarize light are called polarizers.
The light waves of the beam of light that emerges from a polarizer are aligned parallel to the axis of polarizaton of the polarizer. Polarized light can pass undiminished through a second polarizer, called an analyzer, only if the analyzer's axis of polarization is parallel to that of the first polarizer. If the analyzer is rotated so that its axis of polarization is at right angles to that of the polarizer, the light is completely blocked.
Polarizers have a number of pratical uses. The glare outdoors on a sunny day is composed of light partially polarized in a horizontal plane. Sunglasses made of Polaroid plastic have the axis of polarization in a vertical plane. These sunglasses, therefore, block out the polarized glare. Polaroid camera filters block out the polarized portion of the light coming from the sky, thereby darkening the sky in the photograph to increase the contrast between the sky and the clouds. They are also used to reduce glare in water scenes.