A 3D display is any display device capable of conveying three-dimensional images to the viewer. There are many types of 3D displays: stereoscopic 3D displays show a different image to each eye; autostereoscopic 3D displays do this without the need for any special glasses or other head gear; holographic 3D displays reproduce a light field which is identical to that which emanated from the original scene (for the technology, see Computer Generated Holography). In addition there are volumetric displays, where some physical mechanism is used to display points of light within a volume. Such displays use voxels instead of pixels. Volumetric displays include multiplanar displays, which have multiple display planes stacked up; and rotating panel displays, where a rotating panel sweeps out a volume. A wide range of organisations have developed 3D displays, ranging from experimental displays in university departments to commercially available displays. Companies involved include 3DIcon Corporation, Alioscopy, Holografika, MIT Media Lab, NewSight, Pavonine, Philips, QinetiQ, SeeReal Technologies, Sharp, and Spatial View.