Those that are vibrating in more than one direction -- in more than one plane such as both up/down and left/right -- are called unpolarized light.
Generally, unpolarized light can be considered to be vibrating in a vertical and a horizontal plane. To polarize light, one can transmit the light through a polariod filter which will only allow light of single polarity to pass. The resulting light will be polarized light of half intensity. If two polaroid filters are used and placed so that one is rotated 90 degrees to the other, no light will be able to pass.
Some polarization will also occur during reflection, refraction, and scattering of light. When reflecting off non-metallic surfaces, the resulting light will be polarized parallel to the reflected surface. During refraction, a beam of light will be split up into two polarized beams, one polarized parallel and one perpendicular to the boundary. Scattering also causes partial polarization.
Characteristics of Polarization
Polarization is a phenomenon peculiar to transverse waves, i.e., waves that vibrate in a direction perpendicular to their direction of propagation. Light is a transverse electromagnetic wave (seeelectromagnetic radiation ). Thus a light wave traveling forward can vibrate up and down (in the vertical plane), from side to side (in the horizontal plane), or in an intermediate direction. Ordinarily a ray of light consists of a mixture of waves vibrating in all the directions perpendicular to its line of propagation. If for some reason the vibration remains constant in direction, the light is said to be polarized.
It is found, for example, that reflected light is always polarized to some extent. Light can also be polarized by double refraction . Any transparent substance has the property of refracting or bending a ray of light that enters it from outside. Certain crystals, however, such as