LCD projector

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 a modern analog of the slide projector or overhead projector.

Overview

To display images, LCD (liquid crystal display) projectors typically send light from a Metal halide lamp through a prism that separates light to three poly silicone panels -- one each for the red, green, and blue components of the video signal. As polarized 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.The only draw back is that the cheaper bulbs only last about 500 hours where the really expensive ones last around 1000 hours but are about $600

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

The LCD projector was invented by New York inventor Gene Dolgoff. He began working on it in college in 1968 as a way to produce a video projector that would be brighter than the then-available 3-CRT projectors. The idea was to use an element referred to as a "light valve" to regulate the amount of light that passes through it. This would allow the use of a very powerful external light source. After trying many different materials, he settled on liquid crystals to modulate the light in 1971. It took him until 1984 to get an addressable liquid crystal display (LCD), which is when he built the world's first LCD projector. After building it, he saw many problems that had to be corrected including major light losses and very noticeable pixels. He then invented new optical methods to create a high efficiency and high-brightness projector and invented depixelization to eliminate the appearance of the pixels. With patents all around the world, he started Projectavision, Inc. in 1988, the world's first LCD projector company, which he took public on Nasdaq in 1990. He licensed the technology to other companies such as Panasonic and Samsung. This technology and company started the digital projection industry. In 1989 he was awarded the first Darpa contract ($1 million) for proposing that the US HDTV standard should use digital processing and projection. As a member of the National Association of Photographic Manufacturers (NAPM) Standards Subcommittee, IT7-3, he along with Leon Shapiro, co-developed the worldwide ANSI standard for measurement of brightness, contrast, and resolution of electronic projectors.

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.

This technology is employed in some sizes of rear projection television consoles, as there are cost advantages when employed in mid size sets (40 to 50 inch diagonal). This is not expected to have much longevity in the "home theater" marketplace due to expected improvements cost/performance of competing technologies, particularly in direct-view LCD panels at the lower range of sizes and DLP projection in the larger sizes.Verify source|date=July 2007 Another advantage of using this LCD projection system in large television sets is to allow better image quality as opposed to a single 60 inch television, although currently an equal of an LCD projector is the LG 100 inch LCD TV, still in prototype stages this TV is a huge advancement towards projector sized televisions. A common rule of thumb is that an LCD's image quality will decrease with a size increase. Fact|date=February 2008 A workaround is to use a small lcd panel (or panels) and project them through a lens onto a rear projection screen to give a larger screensize with a decreased contrast ratio, but without the quality loss.

In 2004 and 2005, LCD front projection has been enjoying a come-back because of the addition of the dynamic iris which has improved perceived contrast up to the levels of DLP.

The basic design of an LCD projector is frequently used by hobbyists who build their own DIY projection systems. The basic technique is to combine a high CRI HID lamp and ballast with a condenser and collector fresnel, an LCD removed from a common computer display and a triplet.

ee also

*CRT projector
*Handheld projector
*Projector
*Comparison of display technology

Further reading

* cite web | url=http://www.walyou.com/blog/2007/08/29/build-your-own-home-cinema-projector/
title=Build your own home cinema projector | accessdate=2008-06-28 | format=blog entry | publisher=Walyou | date=2007-08-27
author=Ilan Neisse
* cite news | author=Mark Fischetti | title=Two Technologies Shine | url= | format=print | work=Scientific American
publisher=Scientific American, Inc. | pages=110–111 | date=November 2007 | accessdate=2008-06-28
quote=Two technologies—micromirrors and liquid-crystal displays (LCDs)—have been vying for these markets, but they are doing equally well in today's home and business areas....