When my kids asked me how these work, I said "that's easy - the lenses are circularly polarized filters, right for the right eye, left for left eye (or possibly vice-versa)" Indeed that is what Wikipedia says: http://en.wikipedia.org/wiki/3-D_film#Polarization_systems But some simple experiments at home with the glasses leave me confused. e.g. I would have expected that if I put on one pair, and hold the left side of another pair in front of my right eye, I would see nothing, the first filter having let through only the L-component and the second R-filter blocking it. In fact this is what I find: A) Looking at a street sign lit by sunlight outside my window. 1) wearing one pair and holding another pair in front, forwards facing, I see no dimming, whether I hold R in front of R, L in front of R, and whatever angle I rotate the front pair by. (There are some slight colour effects on rotation but nothing dramatic). 2) on flipping the second pair over so the filters are reversed, a) R in front of R has no effect, at any angle b) L in front of R shows compete extinction of the image at rotations of 90 and 270 degrees. The image is considerably dimmed and discoloured at the 0 and 180 points. B) viewing my LCD monitor screen, there is no change from the above, except that R in front of R now gives extinction at 45 and 225 degrees, with a bright image at the intermediate points. Now, can anyone either explain why circularly polarized filters should give these effects, or suggest what other fiendish kind of polarization these devices are using? Also, if anyone else has two pairs of these glasses, could they perhaps repeat the experiment and confirm my observations? (NB these are cheap unpowered glasses with the logo REALD. The lenses are thin plastic which seems to block out about half the brightness of a natural light source. They were obtained at Cineworld, Gloucester, UK).