View source for LCD projector

{{short description|Type of video projector}}
[[File:LCDprojLiesegang3.jpg|thumb|Liesegang 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 equivalent of the [[slide projector]] or [[overhead projector]]. To display images, LCD ([[liquid crystal display|liquid-crystal display]]) projectors typically send light from a [[metal-halide lamp]] through a [[Prism (optics)|prism]] or series of [[dichroic filter]]s that separates light to three [[Polycrystalline silicon|polysilicon]] panels{{spaced ndash}}one each for the red, green and blue components of the video signal. As polarized light passes through the panels (combination of polarizer, polysilicon LCD panel and analyzer), individual pixels can be opened (made transparent controlled by electricity) to allow light to pass or closed (made opaque controlled by electricity) 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 lamp]]s 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 to 15,000 American National Standards Institute (ANSI) lumens. 

Other technologies, such as [[digital light processing]] (DLP) and [[liquid crystal on silicon]] (LCOS) are also becoming more popular in modestly priced video projection.

==Projection surfaces==
Because they use small lamps and the ability to project an image on any flat surface, LCD projectors tend to be smaller and more portable than some other types of projection systems. Even so, the best image quality is found using a blank white, grey, or black{{fact|date=January 2023}} (which blocks reflected ambient light) surface, so dedicated [[projection screen]]s are often used.

[[Color constancy|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.

==Throw ratio==
A projector's [[Throw (projector)|throw ratio]] is used when installing projectors to control the size of the projected display.<ref>{{cite web |url=http://www.theprojectorpros.com/learn-s-learn-p-theater_throw_ratios.htm |title=Throw Ratios and Viewing Distances |accessdate=2009-03-18 |url-status=dead |archiveurl=https://archive.today/20130204013733/http://www.theprojectorpros.com/learn-s-learn-p-theater_throw_ratios.htm |archivedate=2013-02-04 }} Throw</ref> For example, if the throw ratio is 2:1 and the projector is fourteen feet away from the screen, then the display width will be seven feet.

==History==
Early experiments with liquid crystals to generate a video image were done by John A. van Raalte at the [[RCA]]-Laboratories in 1968.<ref>J.A. van Raalte, ''Reflective liquid crystal television display'', Proc. IEEE, Vol. 56, No. 12, pp. 2146–2149</ref> His concept was based on e-beam-addressing to generate an electronic charge pattern corresponding to a video image, which in turn controlled the LC layer of a reflective LC cell. E-beam-addressing requires a [[Cathode-ray tube|CRT]] with a modified faceplate to generate a charge pattern on its surface. No practical application of this concept for projection purposes is known. However, a similar concept was used for [[Cathode-ray_tube#Print-head CRT|print heads]] without an LCD. 

The first experiments with a direct-driven, transmissive matrix-addressed LCD using a converted slide projector by [[Peter J. Wild]] working at [[Brown Boveri]] Research in [[Switzerland]] were conducted in 1971. A projector was shown in operation at the SID Conference 1972 in [[San Francisco]].<ref>P.J. Wild, ''Matrix-addressed liquid crystal projection display'', Digest of Technical Papers, International Symposium, Society for Information Display, June 1972, pp. 62–63</ref> As direct-driven, passive LCDs (without [[thin-film transistor]]s) at the matrix intersections) were not capable of displaying images with sufficient resolution for video pictures, a combination of a fixed image together with an LCD matrix for the variable elements was proposed as an LC projector for certain control room applications,<ref>''Slide sandwiched to liquid crystal gives variable display.'' [[Electronics (magazine)|Electronics]], May 8, 1972, p. 78</ref> with a corresponding patent filed in Switzerland on Dec. 3, 1971.<ref>{{US Patent|3895866}}: Alfred de Quervain, Peter Wild, ''Information-bearing Devices and Projection Display Systems therefor'', filed Nov. 29, 1972</ref>

A lot of effort went into optimizing thin-film transistors (TFT) suitable for [[Active-matrix liquid-crystal display|active matrix-addressed]] (AM) LCDs. The concept was invented and early trials were conducted by teams at [[RCA]] and [[Westinghouse Electric]]. [[T Peter Brody]] left Westinghouse and founded Panelvision in 1981 to manufacture AM LCDs. Breakthroughs occurred elsewhere in new materials and thin-film structures, with [[Hitachi]] of Japan as a pioneering company. Such AM LCDs became commercially available in the early 1980s.

[[File:Gene's Prototype Projector.jpg|thumb|Gene Dolgoff's original LCD Projector prototype.]]
Gene Dolgoff had the idea of using LCDs as light valves in projectors. However, he had to wait until 1984 to get a digitally-addressable LCD matrix device with sufficient resolution and contrast, which is when he completed building his LCD video projector. After building it, he saw many problems that had to be corrected including major light losses and very noticeable pixels (sometimes referred to as the "[[screen-door effect]]"). He then invented new optical methods to create efficient and bright projectors and invented de[[pixelization]] to reduce the screen-door effect.

[[File:Sample-SP.JPG|thumb|Typical 3LCDs (RGB) projector showing separated polarizers]] 
At about the same time, the German company "Bonner Ingenieurbüro für Optoelektronik CrystalVision" started experimenting with LCD projection devices from 1985 onwards. Although traditional slide projectors already used [[infrared filter]]s to reduce heating of the photographic slides, LCDs are much more sensitive to overheating. When the temperature in the nematic liquid crystal layer reaches the "clearing point" (i.e. enters the isotropic phase), the LC light valve does not work anymore until the temperature drops below again. Bernt Haastert, an engineer working at CrystalVision, found out, that placing the required polarizing filters at a certain distance on both sides of the LC cell allowed for efficient air cooling of the arrangement.<ref>{{US Patent|4952925}}: Bernt Haastert, ''Projectable passive liquid-crystal flat screen information centers'', filed Jan. 25, 1988</ref> Without applying this invention, LCD projectors with a powerful light source don't work. A commercial LCD projector based on this principle was launched in Germany in 1990 under the trade name "Imagina 90".<ref>''TV-Kino für jedermann.'' In: Funk + Fernseh Journal, No. 7, July 1989, p. 8.</ref>

With patents filed worldwide (filing his first LCD video projector patent application in 1987), Dolgoff started Projectavision, Inc. in 1988, as one of the world's first dedicated LCD-projector companies, which he took public on [[Nasdaq]] in 1990. He licensed the technology to other companies including [[Panasonic]] and [[Samsung]]. Early pioneers of LCD projection in Japan were Epson and Sharp,<ref>[http://focus.ti.com/download/dlpdmd/166_History_Electronic_Proj_Tech_Hornbeck.pdf]| Hornbeck, TI: ''From cathode rays to digital micromirrors:''A history of electronic projection display technology</ref> which launched their own color video projector products in 1989.

In 1989, Projectavision, Inc. was awarded the first [[Defense Advanced Research Projects Agency]] (DARPA) contract{{spaced ndash}}for [[United States dollar|US$]]1 million{{spaced ndash}}for proposing that the United States [[high-definition television]] (HDTV) standard should use digital processing and projection. As a member of the [[Photographic and Imaging Manufacturers Association|National Association of Photographic Manufacturers]] Standards Subcommittee, IT7-3, Dolgoff along with Leon Shapiro, co-developed the worldwide ANSI standard for measurement of brightness, contrast, and resolution of electronic projectors.<ref>{{cite web | title=Audiovisual Systems – Electronic Projection – Fixed Resolution Projectors (Retired 25 July 2003)|url=https://webstore.ansi.org/standards/i3a/ansinapmit72281997|publisher=ANSI/NAPM|access-date= 28 November 2022}}</ref>

Since 2005,<ref>{{cite web |title=Leading Projector Manufacturers Fujitsu, Hitachi, Panasonic, Sanyo and Sony Join Forces with Epson to Educate the Market about Benefits of Three-Panel Liquid Crystal Display Technology – Projectors Press Releases – Epson Australia |url=https://www.epson.com.au/News/press_releases_details.asp?ID=340&Year=2005 |website=epson.com.au |publisher=Epson |access-date=9 October 2021}}</ref> the only remaining manufacturers of the LCDs for LCD projectors are Japanese imaging companies [[Epson]] and [[Sony]]. Epson owns the technology and has branded it as "[[3LCD]]". To market 3LCD projector technology, Epson also set up a consortium called the "3LCD Group" in 2005 with other projector manufacturer licensees of 3LCD technology that use it in their projector models.

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 transparencies. This provided a stop-gap solution in the era when the computer was not yet a universal display medium, creating a market for LCD projectors before their current main use became popular.

This technology was employed in some sizes of [[rear-projection television]] consoles when there was a cost advantages in mid-size sets (40- to 50-inch diagonal). In 2014, 60-inch 1080p flat panel televisions were less costly than a projector with 1080p native resolution. Projection systems were typically marketed as offering a diagonal image size of 100 to 300 inches.

In 2004 and 2005, LCD front projection began a comeback with the introduction of the dynamic iris and other modifications that have improved perceived contrast to levels similar to DLP.

The basic design of an LCD projector is frequently used by hobbyists who build their own DIY ([[do it yourself|do-it-yourself]]) projection systems. The basic technique is to combine a high [[color rendering index|color-rendering index]] (CRI) [[high-intensity discharge lamp]] (HID lamp) and [[Electrical ballast|ballast]] with a condenser and collector [[Fresnel lens]], a single color LCD removed from a common computer display or electronic device and a [[triplet lens]]. This design can also be used in low cost (around US$200) LCD projectors.<ref>There are several videos on Youtube showing teardowns of these projectors</ref>

==See also==
{{portal|Electronics}}
{{div col|colwidth=30em}}
*[[Comparison of display technology]]
*[[3LCD]]
*[[CRT projector]]
*[[Handheld projector]]
*[[Movie projector]]
{{colend}}
{{clear}}

==References==
{{Reflist}}
*Powell, Evan (2002). "Epson's 730c: Best of Class in 2000-Lumen Portables", projectorcentral.com
*Business Wire (2005). "Leading Projector Manufacturers Fujitsu, Hitachi, Panasonic, Sanyo and Sony Join Forces with Epson to Educate the Market about 
Benefits of Three-Panel, Liquid Crystal Display Technology", projectorcentral.com
*Lawler, Richard (2006). "LG's 100-inch LCD set for mass production", Engadget
*Breeden, John (2009). "LCD monitors go big, with mostly good results", GCN, p.&nbsp;3

==External links==
{{commons category|LCD projectors}}
*[https://projectorwar.com/projector-throw-distance/ Throw Ratio]{{spaced ndash}}article on projector throw and display size ratios.
*[https://www.purple-cat.co.uk/dlp-vs-lcd-projectors-guide/ DLP vs LCD projectors guide]{{spaced ndash}}how do LCD and DLP projectors work and what are their advantages and disadvantages
*[https://projectorwar.com/dlp-vs-lcd-vs-led-vs-lcos/ LCD projectors vs DLP projectors]{{spaced ndash}}easy guide on LCD and DLP technology in projectors and how they compare
*[https://projectorsplace.com/which-is-better-dlp-or-lcd-projector/ Which is Better DLP or LCD Projector]{{spaced ndash}}which is better DLP or LCD projector
* [https://archive.today/20101230012621/http://www.avitav.co.uk/index.php?option=com_content&view=article&id=187&Itemid=246 3LCD Projector Technology]
*{{usurped|1=[https://web.archive.org/web/20221109165144/https://projectorsrating.com/how-many-watts-does-a-projector-use Projector Power]}} – Article on how much power LCD projector consumes

==Further reading==
* {{cite news | author= Fischetti, Mark | title=Two Technologies Shine | work=[[Scientific American]]| pages=110&ndash;111 | date=November 2007 | 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.... }}

{{DEFAULTSORT:Lcd Projector}}
[[Category:Liquid crystal displays]]
[[Category:Projectors]]