Two technologies are currently used to show 3D images on the majority of flat-panel TVs and displays: polarization 3D, which uses a pattern retarder and polarized glasses and is only offered by a small number of display manufacturers; and alternate-frame sequencing, which uses active shutter glasses and requires high refresh rates on displays. Autostereoscopic displays, which use lenticular lenses or parallax barrier technology built into the display panel, and which do not require glasses to view the 3D effect, are used primarily in digital signage and have limited appeal in the consumer market.