Modified Polarizers
Last updated
Last updated
Besides being turned transparent, LCD’s have another trick up their sleeve involving light polarization. By removing one of the polarization layers, the screen will look white to a viewer until they look through another polarizer. Below, I’ll attempt to describe how this works.
A full explanation of the science behind wave polarization is a little bit outside of the scope of this book, but there is more information in the appendix. This video is a pretty solid explanation of polarized light and its usage with cameras. I encourage you to look into it because there are a lot of other great effects that can be employed via polarization. My explanation will be simplified in order to stay concise.
You may remember from Physics class that light sometimes behaves as a particle, and sometimes as a wave. This light wave has a frequency, an amplitude and a rotation or polarization. As stated before, an LCD works by employing a backlight, a pair of linear polarizers, and a liquid crystal layer. When all of the light particles come off the backlight, they do not have a uniform polarization — they are just going all over the place. As they pass through the back polarizer, specialized molecules embedded in thin columns absorb any light that doesn’t have a particular polarization. The polarized light then passes through the liquid crystal layer. When the liquid crystal receives current, its molecular structure changes and it provides a transparent tunnel that can be variably twisted. The twist in the liquid crystal gives us a way to electronically modulate the rotation of the light wave.
As the light exits the liquid crystal and arrives at the front polarizer — this is where the magic happens. The front polarizer is the exact same material as the back polarizer, but its physical orientation is perpendicular to the back polarizer. This offset orientation effectively blocks or absorbs light of a particular polarization. If the light passes through the liquid crystal without being twisted, you will get a black pixel. If the liquid crystal twists the light 90º so that it passes through the front polarizer — you will get a white pixel. With the red/green/blue color filters on each pixel, the video signal is able to tune the wave orientation passing through each color to produce the millions of colors we see on an average display. Again — this is a very simplified explanation that glosses over a lot of important details related to different LCD technology.
So with all of the above in mind — if we remove the front polarizer, what happens? Now there is nothing to absorb the light that passed through the front polarizer and the viewer will just see white light. However, if you put a polarizer back in front of the screen, everything will appear normal again. This polarizer doesn’t need to be right on top of the screen either. The polarizer can be in glasses that the view puts on or it can be placed meters away from the screen.
There are a lot of interesting possibilities available for these screens, but actually getting one to try is another matter. See my notes in the appendix on how you might make one yourself from an existing LCD. Fuse Technical Group is one vendor that offers these displays as a rentable or purchasable product and they are branded as WhiteSpace displays.
This technology is great for an unusual reveal to the viewer since it just looks like a white screen otherwise. The polarizing film can be placed at any distance from the screen and still allow the screen content to be visible, as long as the film is between the viewer and the modified LCD. You’ll notice that depending on the way that the film is rotated relative to the screen, you can get things like inverted or warped colors since you are blocking different orientations of light. Also, due to the properties of polarized light, the content can be seen via the reflection off of other objects, or if you stick the polarization film on top of a mirror.
The artist Flavien Théry has some amazing pieces that employ modified LCD’s and polarization film. In his piece La Porte he has a small door shaped object made of reflective material on top of a modified screen and the content is only viewable through the reflection on the door.
The artist Ryo Kishi also has several projects that also explore create applications of polarizing film. His dis:play(bias) piece uses geometric elements covered in polarizing material to reveal the images. Breathing Frame uses small pinwheels fashioned from the material to display the content on screen.
Unrelated to LCD monitors, light polarization is also a technique that can be used with projectors as well. Many 3D movies in cinemas have different systems to pass the light through a polarizer (either dual projectors with separate polarizers, or a spinning polarizer in sync with the framerate). To preserve the polarization of the light, many of these setups also require a specialized silver screen material or paint. The view is usually given either passive (each eye has a polarizer in a different orientation) or active glasses (which shutter each eye in sync with the projector) to ensure that each eye sees the image that is intended for it. I haven’t found a good shareable example of polarized projectors being used in an unusual or artistic way, but there are definitely some possibilities out there.
There are also artists that have explored the use of polarizing filters and material that either forgo the use of a digital display and just use a backlight, or they just use natural light. While these are not necessarily a display technology, they felt related enough to mention here. The principle is the same in that when a polarizer is viewed through another polarizer, their rotation relative to eachother will determine the amount of light that is passed through. If you layer something like thin cellophane on top of a polarizer, you can also distort the lightwaves and shift the color. If one polarizer is physically rotated, you can also generate rudimentary animations or motion on the other surface.
Examples:
