Consumer Reports has posted a short video clip that shows their preliminary tests of Panasonic 3D plasma and Samsung 3D LCD TVs. You can find it here.

http://www.consumerreports.org/cro/video-hub/electronics/televisions/16935238001/

During the clip, they point out that while both technologies exhibit high contrast 3D images, the Samsung images essentially go black if the viewer lays down while watching TV with 3D glasses. (This puts the polarization axis of the glasses at 90 degrees to the screen, and is not recommended in any case!)

Performing the same test with the Panasonic plasma resulted in a slightly dimmer image, and nothing more.

There’s an easy explanation as to why this happens with LCD TVs. Liquid crystals can only shutter light that is already polarized, which is why each LC pixel element has two polarizers – one mounted at the rear of the pixel wall, and one at the front. Rotating a pair of active shutter glasses 90 degrees in front of the screen in effect acts as a third light shutter and cancels out whatever light remains after the LC imaging process.

Ever hold two pairs of polarized sunglasses at right angles to each other? Then you’ve seen the same effect.

Now, let me state that lying down on your side while watching 3D is a pretty dumb idea all around. The images are oriented in the wrong axis with respect to your vision, and it’s also got to be uncomfortable!(Come on, how lazy can one get?)

Even so, this video demonstrates clearly that moderate changes in polarization angles make images from 3D LCD TVs noticeably darker, so if you tilt your head to one side or the other while wearing glasses and watching a 3D LCD TV, you will experience this effect.

Why doesn’t this happen with plasma? Because it doesn’t use polarized light, just a burst of light from color phosphors. OLED 3D TVs (if and when they ever get here) are also free from this cross-polarization problem.

This is another example of why 3D TV needs to be thoroughly explained to potential buyers so that they don’t run into any unpleasant surprises after the sale.