Head-mounted Displays

A Head-mounted Display (HMD) is generally a display of computer that one wears on his head. They are what they are names after. Mostly these HMDs are placed or attached on helmets or even on the goggles. They are specially designed keeping many things in mind. Engineers have designed them to make sure that wherever the user points his head at and see wherever direction he feels like the monitor will remain in front of his eyes all the time. Mostly all HMDs consist of a screen for individual eye and that is what creates a sense any images the user looks at has some depth. It appears to be highly three dimensional or real-life like sized.
The monitors that a HMD uses are usually made up of Liquid Cystal Display (LCD). However older monitors are also found that are made up of displays of Cathode Ray Tube (CRT). The LCD monitors generally are lightly weighted, compact, more efficient and lot much inexpensive than the CRT displays.  However there are two more advantages that a CRT display has as compared to a LCD. Those are the screen resolution as well as the brightness. The displays of CRT are mostly heavy and bulky. This causes usage very uncomfortable. The HMDs that are counted on them are used with great difficulty. It needs a mechanism of suspension to assist in shifting the heavy weight for easy usage. However this suspension mechanism limits the movement of the user. This can again destroy the feeling of immersion.
There are other HMDs that use different technologies. They are:-

• Vacuum Fluorescent Displays (VFD)
• Fiber-Optics Displays
• Virtual Retinal Displays (VRD)
• Digital Micromirror Device (DMD) Displays
• Electroluminescent Displays
• Electrophoretic Displays (EP Displays)
• Field Emission Displays (FED)
• Plasma Displays
• Electrochromism Displays (EC Displays)
• Light Emitting Diode (LED) Displays

Display technologies are very rarely used by engineers in HMDs. They have the drawback of limited brightness as well as resolution. There are few that produce nothing more than a monochromatic image. Like the VRD there are also few plasma display technologies that work very well with HMDs. However these are too expensive to be afforded.
These HMDs mostly include speakers or headphones. This is included to make sure both audio and video output is received. The high-end HMDs are attached to the CPU of the VR systems through cables.  These wireless systems, however, do not have the eligibility to avoid lag. They always use a device to track as the user moves in whatever direction the point of view of the monitor also changed.  There are other systems that use particular types of goggles or glasses along with the other display monitors.