Editing Head-mounted display (section)

== Overview ==
[[File:EYE-SYNC eye-tracking analyzer.JPG|thumb|An eye tracking HMD with [[Liquid-crystal display|LED]] illuminators and cameras to measure eye movements|alt=]]

A typical HMD has one or two small displays, with lenses and semi-transparent mirrors embedded in eyeglasses (also termed data glasses), a visor, or a helmet. The display units are miniaturized and may include [[cathode-ray tube]]s (CRT), [[liquid-crystal display]]s (LCDs), [[liquid crystal on silicon]] (LCos), or [[organic light-emitting diode]]s (OLED). Some vendors employ multiple micro-displays to increase total resolution and [[field of view]].

HMDs differ in whether they can display only [[computer-generated imagery]] (CGI), or only live imagery from the physical world, or combination. Most HMDs can display only a computer-generated image, sometimes referred to as virtual image. Some HMDs can allow a CGI to be superimposed on real-world view. This is sometimes referred to as [[augmented reality]] (AR) or [[mixed reality]] (MR). Combining real-world view with CGI can be done by projecting the CGI through a partially reflective mirror and viewing the real world directly. This method is often called optical see-through. Combining real-world view with CGI can also be done electronically by accepting video from a camera and mixing it electronically with CGI.

By using AR technology, the HMDs are allowed to achieve a see-through display. By using virtual reality (VR) technology, the HMDs can realize viewing the images in 360 degrees.<ref>{{Cite journal |last=Komura |first=Shinichi |date=2024-07-19 |title=Optics of AR/VR using liquid crystals |journal=Molecular Crystals and Liquid Crystals |volume=768 |issue=17 |language=en |pages=1014–1039 |doi=10.1080/15421406.2024.2379694 |issn=1542-1406|doi-access=free |bibcode=2024MCLC..768.1014K }}</ref>