Video projector

Encyclopedia : V : VI : VID : Video projector

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A video projector takes a video signal and projects the corresponding image on a projection screen using a lens system. All video projectors use a very bright light to project the image, and most modern ones can correct any curves, blurriness, and other inconsistencies through manual settings. Video projectors are widely used for conference room presentations, classroom training, and home theatre applications.

Video projectors may also be built into cabinets which use a rear projection screen to form a single unified display device, now popular for "home theater" applications.

Common display resolutions for a portable projector include SVGA (800x600 pixels), XGA (1024x768 pixels), and 720p (1280x720 pixels).

The cost of a device is not only determined by its resolution, but also by its brightness. While most modern projectors will provide sufficient brightness at night or under controlled lighting such as in a basement with no windows[Lumens guide]. ProjectorPeople.com., a projector with a higher lumens rating is required for a room with a higher amount of ambient light. A rating of 1000 to 1500 ANSI lumens or lower is suitable for smaller rooms with controlled lighting or low ambient light.[Buying guide]. TvSpecialists.com. Between 1500 to 3000 ANSI is suitable for medium sized rooms with some ambient light or dimmed light. Over 3000 ANSI is appropriate for very large screens in a large room with no lighting control (for example, a conference room). Projected image size is also important, as the total amount of light does not change, as size increases, brightness decreases. An increase in a widescreen image from 80 inches diagonal to 100 inches diagonal reduces the image brightness by 35 percent.

Projection technologies

• CRT projector using cathode ray tubes. This typically involves a blue, a green, and a red tube. Minimal maintenance is required (unlike projectors that use lamps), although it is seen most often in very expensive (over $10,000) fixed systems.
• LCD projector using LCD light gates. This is the simplest system, making it one of the most common and affordable for home theaters and business use. Its most common problem is a visible "screen door" or pixelation effect, although recent advances have minimized this.
• DLP projector using Texas Instruments' DLP technology. This uses one, two, or three microfabricated light valves called a Digital Micromirror Device (DMD). The single and two DMD verions use rotating color wheels in time with the mirror refreshes to modulate color. The most common problem with the single or two "chip" varieties is a visible "rainbow" visible to some people when they move their eyes. Systems with 3 DMDs never have this problem. More recent projectors with higher speed (2x or 4x) and otherwise optimised color wheels have minimized this artifact.
• LCOS projector using Liquid crystal on silicon.
• D-ILA JVC's Direct-Drive Image Light Amplifier.

The current dominant technology for expensive (over $5,000) portable digital projectors is Texas Instruments' DLP technology, with LCD projectors dominating the less expensive (under $2,500) market segment. This is due mainly to the high quality of systems using 3 separate color wheels, which greatly increases the cost. DLP systems currently cannot be produced inexpensively enough to compete widely in the budget market ($800). DLP High intensity CRT devices are suitable only for fixed installations.

Obsolete technologies

• Eidophor oil-film projectors

• GE Telaria oil-film projectors

• Hughes-JVC Technology ILA (Image Light Amplifier) light valves.

See also

• Projector for a directory of projector types
• Projection screen
• Screen door effect
• Comparison of display technology

References

 

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