Nintendo revealed the 3DS today at their keynote, and, as expected, it features a 3D screen without glasses. What the Big N didn’t reveal is how it all works, which leaves it open to speculation. According to Engadget, the effect is achieved using a parallax barrier LCD from Sharp. The displays have been used in cell phones in Asia for a few years, but are only practical on a small screen. The viewing angle is very specific, and isn’t suited to a living room TV at all.
With normal 3D, viewers have to wear those dorky glasses that make each eye see a different image, just like they do with everyday objects. The process fools the brain into perceiving depth. The way the Sharp LCD works is much more like those holographic baseball cards, where moving the card side-to-side produces a different image. The parallax barrier directs the light from the LCD in two directions, half towards the right eye and half towards the left. Since each eye is now seeing a different image, the brain can perceive depth.
This technology only works when the viewer is relatively close to the screen, and only at a very specific angle, so you can expect to continue wearing glasses at the theatre for a while.