Pulfrich Effect: Deception On TV?
For the sake of completeness and topicality, a technology that is often used on television to raise interest in the subject of 3D is described below.
Although this technology can be used to achieve good spatial impressions, it is not stereo 3D as there are no different images for the right and left eyes.
The Pulfrich effect is an optical illusion based on the fact that the brain takes a little longer to recognize dark optical stimuli as opposed to light ones.
The special thing about recording using the Pulfrich effect is that either the camera or the object being filmed (a person, animal, car, etc.) moves consistently in a certain direction.
The secret of the Pulfrich effect 3D glasses is merely that one eye is darkened. Although both eyes see the same image, the darkened eye transmits the image to the brain somewhat later. The brain calculates spatial depth information from this parallax that does not actually exist.
When the movement stops, however, only two dimensions are visible - even with 3D glasses! More explanations at: The Pulfrich Effect )
The special thing about relevant content, and what makes it really interesting, is the fact that you really do get a certain spatial impression with the "3D glasses" - while an observer without the glasses still has unrestricted 2D vision. This is NOT possible simultaneously with all stereo 3D displays.