Explaining Passive 3D TV Technology
In this case, asking "How does 3D TV work?" is like asking how 3D movies in the theater work. The technology behind passive 3D TV is similar to how 3D movies are presented in cinemas. Two slightly different images--one for each eye--comprise each frame displayed by the TV. One is displayed so that it is polarized vertically, and the other is polarized horizontally.
The 3D glasses used by passive 3D TVs are just like those used in the theater and do not require any power. Each lens in the glasses is polarized to let a different image through, one horizontal and one vertical. When each eye sees a slightly different version of the same combined frame, the illusion of 3D is created.
Since they don't require any power or contain any electronics, passive 3D glasses are very inexpensive and easily replaceable. This distinction is often key in figuring exactly how a 3D TV works into your budget.Explaining Active 3D TV Technology
The technology behind active 3D TV is more advanced than that used to deliver passive 3D TV. How does 3D TV work differently with active glasses? Rather than display two images at once--one meant for the left eye and another for the right eye-- like passive 3D TV tech, active 3D TV tech very quickly switches the on-screen image between one for the left eye and one for the right eye.
In order to create the 3D effect, you wear special active 3D glasses that have a power source (usually a battery) and lenses with a layer of liquid crystal on them. (How does 3D TV work when the battery in the glasses runs out? Answer: It doesn't.) By sending power to this liquid crystal "shutter," each lens can be made transparent or opaque.
The active 3D glasses communicate wirelessly with the 3D TV in order to synchronize the switching of the lenses from see-through to dark, so that each eye only sees the frame it's supposed to when it appears on screen. This happens very quickly so that there's no noticeable flickering as the shutters switch on and off. Because of how 3D TV works in this case, the image quality is generally believed to be higher using this technology.Explaining Glasses-free 3D TV Technology
Glasses-free or autostereoscopic 3D TV is not widely available now, but it's considered by some to be the future of 3D TV because it doesn't require viewers to wear glasses. How does 3D TV work in this case? It most commonly uses a technology called "parallax barrier."
Parallax barrier refers to a special material on the screen with tiny slits in it that allow one image to be shown only to the left eye and another image to be shown only to the right eye. These slightly different images are what create the 3D effect when viewed at the same time. This is the same technology that is used in Nintendo's 3DS handheld video game system, only in much larger form.
While it may sound like the most ideal type of 3D TV, a TV using a parallax barrier requires that the viewer be looking at it from just the right angle. How does 3D TV work for multiple- or off-angle viewers in this scenario? Not well. Even the slightest change in the viewing direction can degrade or eliminate the 3D effect.
Nintendo's 3DS gets around this problem by including a slider to adjust the parallax barrier. 3D TVs need to be viewable by multiple people at the same time, so such an adjustment isn't possible. This makes glasses-free viewing on the large screen largely impractical for now.
Glasses-free 3D TV makers are researching ways to increase the acceptable viewing angle for this type of 3D TV. In the meantime, these TVs remain luxury items priced at several times that of a comparably sized passive or active 3D TV.Don't Forget: Required Equipment
The question of "How does 3D TV work?" isn't fully answered without a look at the most important pieces of the puzzle apart from the TV itself: source material for 3D content, and compatible players. Right now, there are three main ways to get 3D content on a 3D TV: 3D Blu-ray players, cable boxes that support 3D programming, and 3D-capable video game consoles such as the Sony PlayStation 3.
Of course, movies and games specifically made for 3D are crucial to how a 3D TV works. Many films that were presented in 3D in the theater are available as 3D Blu-rays, but the number of 3D video games remains relatively small. Since the 3D ecosystem for home viewing is still relatively new, you should expect the amount of content on offer in 3D to increase over time.