Have you ever watched a movie in 3D at a movie theatre? You probably had to wear special glasses in order to get that 3D effect. And if you take them off, the movie looks completely blurry.
The most common way of producing the 3D image is through the use of polarized filters. This principle works by projecting the movie from two different perspectives at the same time, with the light being polarized in a different way in each projection. The polarization refers to the orientation the waves are travelling in, which means multiple light waves of different polarizations can be still travelling in the same direction!
Depiction of how polarizing filters can select for waves of a certain polarization. Credits: Wikimedia
Two filters oriented in the same direction will block little light, as shown in figure 1. However, when they are oriented 90 degrees to each other, they will block out almost all light, as shown in figure 2. This does not work with non-polarized filters (figures 3 and 4). Credits: Wikimedia
By using 3D glasses where each lens filters light of different polarizations, your eyes can receive two different perspectives of the same scene. Your brain combines these images together so you can see a single 3D image.
The next time you go to watch a movie in 3D, try keeping the glasses and experimenting with them. You’ll find that there are many sources of polarized light around you, and that the orientation of the glasses can change the way light goes through them!