LCD Projectors

An LCD projector is a type of video projector for displaying video, images or computer data on a screen or other flat surface. It is the modern equivalent of the slide projector or overhead projector. more...

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Overview

To display images, LCD (liquid crystal display) projectors typically send light from a Metal halide lamp through three LCD panels -- one each for the red, green, and blue components of the video signal. As polarised light passes through the panels (combination of polarizer, LCD panel and analyzer), individual pixels can be opened to allow light to pass or closed to block the light. The combination of open and closed pixels can produce a wide range of colors and shades in the projected image.

Metal Halide lamps are used because they output an ideal color temperature and a broad spectrum of color. These lamps also have the ability to produce an extremely large amount of light within a small area: current projectors average about 2,000-4,000 ANSI lumens.

Newer technologies, such as DLP and LCOS are becoming more popular in video projection. In practice, the term "LCD Projector" is often used as a catch-all for any type of computer projector, regardless of the technology being used.

Projection surfaces

Thanks to small Metal Halide lamps and the ability to project an image on any flat surface, LCD projectors tend to be smaller and more portable than other types of projection systems. Even so, the best image quality is found using a blank white or grey surface, so dedicated projection screens are often used.

Perceived color in a projected image is a factor of both projection surface and projector quality. Since white is more of a neutral color, white surfaces are best suited for natural color tones; as such, white projection surfaces are more common in most business and school presentation environments.

However, darkest black in a projected image is dependent on how dark the screen is. Because of this, some presenters and presentation space planners prefer gray screens, which create higher perceived contrast. The trade-off is that darker backgrounds can throw off color tones. Color problems can sometimes be adjusted through the projector settings, but may not be as accurate as they would on a white background.

History

Early LCD systems were used with existing overhead projectors. The LCD system did not have a light source of its own: it was built on a large "plate" that sat on top of the projector in place of the transparencies. This provided a stop-gap solution in the era when the computer was not yet the universal display medium, creating a market for LCD projectors before their current main use became popular.

Read more at Wikipedia.org