Light is an electromagnetic wave, composed of electric fields. A single wave of light only oscillates in one direction, while a ray of light, which contains a myriad of light waves oscillates in many directions. When light, whether it be a singular wave or multiple, only oscillates in one direction, it is polarized.
Also known as “polarization by use of a polaroid filter,” the most common method of polarization is polarization by transmission. A polaroid filter is composed of a thin plastic material, and as evident by its name, “polarizes” light.
If two polarizing filters are placed perpendicular to each other, then no light would pass through. This happens because the first filter would only let light polarized in one direction through, while the second would only let light oscillating in the perpendicular direction through. Thus, no light would pass through, leaving the area of intersection between the two filters pitch black.
Polarizing filters have many surprisingly interesting applications, ranging from sunglasses to making 3D movies possible.
When light reflects off a surface, it is polarized. This phenomenon is known as “polarization by reflection.” A combination of polarization by reflection and transmission come into play regarding polarized sunglasses. Polarized sunglasses are meant to reduce glare consist of the lens being a vertically oriented polaroid filter. When light bounces off a horizontal surface, it is horizontally polarized. Thus, if the sunglasses only let vertically polarized light through, then the glare doesn’t reach the user’s eyes. Using this same principle, what if one of the filters in polarized sunglasses is rotated 90 degrees. Thus, each lens lets light polarized in completely different directions through. This is how 3D glasses work. In real life, our left and right eye see slightly different images, creating the perception of 3D. 3D movies, likewise, display two images, one polarized vertically, the other horizontally. When generally looking at the screen with special glasses, it may appear blurry, but with 3D glasses, the characters seem to jump out!