Polarised 3D glasses and an LCD Monitor

[ratata]

Hi,

I was looking through a pair of 3D movie glasses (the polarised sort) while looking at my lcd monitor. I was confused by a couple of things:
- When I tilt the glasses 45 degrees from horizontal, the image in both lenses turned blue, and when i tilted the glasses 45 degrees from horizontal the other way, the image in both lenses turned orange/red. I thought that one lens should be orange/red while the other is blue, not the same colour at the same time.
- When I turn the glasses around so that I am looking in the wrong direction through the lens, and then do the 45 degree tilt as above, both lenses either turn black (no light passes through) or remain clear. I thought that they should behave the same no matter which way you look through them.

I have done a little reading and found that lcd screens use polarising filters but i can't get my head around the above two observations. I hope someone can tell me what is going on!

Thanks for your help.

 

[Neo_Anderson]

Welcome to the Forum, ratata, and a very interesting observation!
Yes, I observed the same thing when messing with polarizers pulled off a hand-held videogame. What did I find out? I found out that these polarizers (made by mechanically stretching a polymer as it's solidifying) have a protective, transparent film on one side. On the unprotected side, you'll observe black-to-transparent, and on the protected side, you'll see blue-to-red. This is due to dichromism; by the interference of the light through the protective film/polarizer interface.

You may peel the polarizer from its protective film using a hydrocarbon-based solvent.

Both glasses polarizers act in unison as you rotate them, true, but they are aligned the following way: Left lens has its polarizer oriented at 22.5-degrees, and the right lens has its polarizer oriented at 68.5-degrees. This way, both polarizers will block out light in unison as they are rotated, while being oriented by these two, different degrees. As you know, these two different degrees of orientation of the lenses in the glasses (22.5 and 68.5 degrees) are what sends left-channel video (22.5 degrees) to your left eye, and right-channel video (68.5 degrees) to your right eye.