A TV set that renders stereoscopic 3D content using active or passive eyeglass technology. Active 3D TVs use shutter glasses that synchronize with the TV set to open and close each lens at the right time. Passive 3D TVs use less costly polarized glasses that separate the stereo frames by polarization. Although they have not become mainstream, there are 3D technologies that do not require glasses (see Ultra-D).3D Sets Hit the Stores in 2010Active 3D TVs were introduced in the U.S. in the 2010 time frame, and passive 3D TVs emerged in 2011. All 3D plasma TV sets used the active 3D method. For more details, see active 3D, polarized 3D and 3D visualization.