Currently there are two types of 3D TVs available on the market:
Active 3D TVs work by alternately displaying a frame for the left eye and right eye in sync with the 3D glasses. The active 3D glasses ensure that each eye only sees the picture it is meant to see by simultaneously blacking out one eye then the other. This is all done at a rate of at least 120 times per second so that the person wearing the glasses in unaware that this is happening.
Active shutter glasses are typically powered by a battery and are generally are a little heavier than the passive glasses.
Sony, Samsung, Panasonic and LG manufacture active 3D TVs.
Passive 3D TVs work by simultaneously displaying the frame for both eyes at the same time. The passive glasses are able to discern between the two frames and ensure each eye sees the picture it is supposed to see. Passive glasses are the same type of glasses that are used at most movie theatres in North America. In fact, you can use the glasses you get at the movie theatre with passive 3D TVs.
One of the disadvantages of passive 3D TVs is that since the TV must display both images at the same time, the resolution of the picture is halved. Therefore passive 3D TVs are unable to display full HD 3D picture quality.
Currently LG and Vizio are the only companies that manufacture passive 3D TVs. Passive 3D TVs just started hitting the market in Q4 2010.