3D Television Technology

Polarization of Light: Videos

Linear polarizers, or polaroids, are sheets of semi-transparent material which only allow light through of the correct linear polarization. All light with linear polarization perpendicular to the sheet's polarization axis is blocked. By putting two polaroids in series, as shown in the video below, it is possible to block all incident light. The light striking the first polarizer is linearly polarized in one direction, and as the second polarizer is rotated, it will reach a point where it is perpendicular to the first and will block all the light.

Natural light from the sun or light from an incandescent light bulb is randomly polarized, with light rays of no particular polarization. Useful for home experiments with polarization of light is the fact that light from an LCD screen has a constant linar polarization, as shown in the below video where a polaroid is rotated in front of a laptop screen. This will also work with most cell phones and high-definition TVs. Note that the light is not circularly polarized, as needed for 3D effects, and as such LCD screens alone cannot be used for passive polarization 3D effects.

Florida State University hosts an interactive applet showing how polaroids block polarized light. The Java applet shows two linear polaroids with unpolarized light incident upon them. With the ability to adjust the angle of the polaroids, it is possible to allow all light of a particular polarization to pass, or completely block the light.

There is the rare occasion where the worlds of art and science collide. Polarization art just happens to be one of them. Austine Studios specializes in polarized light art, with a video on their main page showcasing the art very elegantly. The principles behind it, however, can be easily seen in the classroom.

A simple test is shown in the video below. The only materials needed are two polaroids, a transparent projector sheet and regular Scotch tape. The Scotch tape is a bifringent material. This means that when light passes through it the angle of polarization is rotatated. The degree of rotation depends on the wavelength of the light (recall from the wave nature page that the wavelength determines the colour of the light). By placing pieces of the tape on the transparent sheet at varying thicknesses and placing the sheet in front a polaroid, the polarization of light through the sheet will be linear but with an angle varying with colour. When a second polaroid is placed in front of the sheet, as it is rotated different colours appear at different angles, never fully blocking out all light. This can be seen in the video below and is easy to try with any set of two polaroids (or a laptop screen and one polaroid, as seen in the video). Try it with a clear CD case to see something really cool!

OK, so thats what polarization and polarizers are, so what? What does that have to do with seeing the 3D image on the screen? By linking polarizers and how the human eye perceives depth, it is indeed possible to trick the eye with two sets of images. To test your knowledge on polarization, try the quick polarization quiz. To see how the brain perceives depth, continue on to learn about stereopsis. If you want to see how polarization is used in 3D display and already know how depth perception works, skip ahead to how passive polarization works.