Well, it polarizes the light for each frame. They polarize the left eye's frame horizontally, the right vertically. each lens is designed to only allow light that is polarized a certain way through. so, the left eye's lens will be horizontal, the right vertical. this prevents each eye from seeing the frames the other eye was meant to see, allowing for 3D.

in order for this to work though, the projector, screen, and glasses all have to be built for polarized light. the projector has to be able to send out frames polarized a certain way, the screen has to be built to reflect the polarized light back correctly, and then the glasses to screen out the frames that eye isn't meant to see.

In the case of these TV's, they just make the screen polarize the light, then you use the glasses to get 3D. Many current polarized 3DTV's end up losing half their resolution due to the polarization effect (which is fine for gaming, since you won't get 3D in full 1080p this generation), however TV manufacturers are now coming out with sets that are polarized at full 1080p. The sets cost a bit more than conventional LCD active shutter glasses based 3DTV's, but the glasses are so much cheaper that it offsets the cost. You can spend $10 and have enough pairs of glasses for the entire family and any guests that might come over.