LCD projector
An LCD projector is a type of video projector
Video projector
A video projector is an image projector that receives 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...

 for displaying video, images or computer data on a screen or other flat surface. It is a modern equivalent of the slide projector
Slide projector
A slide projector is an opto-mechanical device to view photographic slides. Slide projectors were common in the 1950s to the 1970s as a form of entertainment; family members and friends would gather to view slide shows...

 or overhead projector
Overhead projector
An overhead projector is a variant of slide projector that is used to display images to an audience.-Mechanism:An overhead projector typically consists of a large box containing a very bright lamp and a fan to cool it. On top of the box is a large fresnel lens that collimates the light...

. To display images, LCD (liquid-crystal display
Liquid crystal display
A liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....

) projectors typically send light from a metal-halide lamp through a prism
Prism (optics)
In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...

 or series of dichroic filter
Dichroic filter
A dichroic filter, thin-film filter, or interference filter is a very accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, dichroic mirrors and dichroic reflectors tend to be characterized by the color of light that they...

s that separates light to three polysilicon
Polycrystalline silicon
Polycrystalline silicon, also called polysilicon, is a material consisting of small silicon crystals. It differs from single-crystal silicon, used for electronics and solar cells, and from amorphous silicon, used for thin film devices and solar cells....

 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 to 15,000 American National Standards Institute
American National Standards Institute
The American National Standards Institute is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organization also coordinates U.S. standards with international...

 (ANSI) lumens
Lumen (unit)
The lumen is the SI derived unit of luminous flux, a measure of the total "amount" of visible light emitted by a source. Luminous flux differs from power in that luminous flux measurements reflect the varying sensitivity of the human eye to different wavelengths of light, while radiant flux...


Other technologies, such as Digital Light Processing (DLP) and liquid crystal on silicon
Liquid crystal on silicon
Liquid crystal on silicon is a "micro-projection" or "micro-display" technology typically applied in projection televisions. It is a reflective technology similar to DLP projectors; however, it uses liquid crystals instead of individual mirrors. By way of comparison, LCD projectors use...

 (LCOS) are also becoming more popular in modestly priced video projection.

Projection surfaces

Because they use 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 some other types of projection systems. Even so, the best image quality is found using a blank white, grey, or black (which blocks reflected ambient light) surface, so dedicated projection screen
Projection screen
A projection screen is an installation consisting of a surface and a support structure used for displaying a projected image for the view of an audience. Projection screens may be permanently installed, as in a movie theater; painted on the wall; or semi-permanent or mobile, as in a conference room...

s 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.


A projector's throw ratio
Throw (projector)
In film terminology, throw is the distance of a movie projector from the screen. It is the distance the image is thrown onto the screen, and it has a large effect on screen size....

 is used when installing projectors to control the size of the projected display. 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.


The LCD projector was invented by American inventor Gene Dolgoff
Gene Dolgoff
Eugene Dolgoff is the founder, CEO, and CTO of The 3D Source, Inc., involved in the printing of 3-D moving images for advertising and promotions, labels, financial payment and ID cards, and medical imaging. He holds the same position in 3-D Vision, Inc., which is involved with the development of...

. 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
Light valve
A light valve is a device for varying the quantity of light, from a source, which reaches a target. Examples of targets are computer screen surfaces, or a wall screen in the case of a light projector....

" 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 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 (sometimes referred to as the "screen-door effect
Screen-door effect
The screen-door effect or fixed-pattern noise is a visual artifact of the projection technology used in digital projectors, where the fine lines separating the projector's pixels become visible in the projected image...

"). He then invented new optical methods to create high efficiency and high-brightness projectors (now used in most digital projectors) and invented depixelization
Pixelization is a video- and image-editing technique in which an image is blurred by displaying part or all of it at a markedly lower resolution. It is primarily used for censorship...

 to eliminate the appearance of the pixels.

With patents all around the world (filing the first LCD projector patent application in 1987), he started Projectavision, Inc. in 1988, the world's first LCD-projector company, which he took public on Nasdaq
The NASDAQ Stock Market, also known as the NASDAQ, is an American stock exchange. "NASDAQ" originally stood for "National Association of Securities Dealers Automated Quotations". It is the second-largest stock exchange by market capitalization in the world, after the New York Stock Exchange. As of...

 in 1990. He licensed the technology to other companies including Panasonic
Panasonic is an international brand name for Japanese electric products manufacturer Panasonic Corporation, which was formerly known as Matsushita Electric Industrial Co., Ltd...

 and Samsung
The Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...

. This technology and company started the digital-projection industry.

In 1989, he was awarded the first Defense Advanced Research Projects Agency
Defense Advanced Research Projects Agency
The Defense Advanced Research Projects Agency is an agency of the United States Department of Defense responsible for the development of new technology for use by the military...

 (DARPA) contract for US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....

1 million for proposing that the United States high-definition television
High-definition television
High-definition television is video that has resolution substantially higher than that of traditional television systems . HDTV has one or two million pixels per frame, roughly five times that of SD...

 (HDTV) standard should use digital processing and projection. As a member of the National Association of Photographic Manufacturers
Photographic and Imaging Manufacturers Association
The Photographic and Imaging Manufacturers Association, or PIMA, was founded in 1946 under the name National Association of Photographic Manufacturers . In 1997 the name was changed to PIMA....

 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.

Currently the only remaining manufacturers of the LCDs for LCD projectors are Japanese imaging companies Epson and Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....

. Epson owns the technology and has branded it as "3LCD
3LCD is the name and brand of a major LCD projection color image generation technology used in modern digital projectors. 3LCD technology was pioneered and refined by Japanese imaging company Epson in the 1980s and was first licensed for use in projectors in 1988...

". 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 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
Rear-projection television
Rear-projection television or RPTV is a type of large-screen television display technology. Up until the mid-2000s, most of the relatively affordable consumer large screen TVs up to used rear-projection technology...

 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
Home theater
A home theater or home theatre is a theater built in a home, designed to mimic commercial theater performance and feeling, more commonly known as a home cinema...

 marketplace due to expected improvements in cost and performance of competing technologies, particularly in direct-view LCD panels at the lower range of sizes and DLP projection in the larger sizes. Another advantage of using this LCD-projection system in large television sets is to allow better image quality as opposed to a single sixty-inch television, although currently an equal of an LCD projector is the LG 100-inch LCD TV, still in prototype stages this television 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. 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 screen size with a decreased contrast ratio, but without the quality loss.

In 2004 and 2005, LCD front projection was 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 (do-it-yourself
Do it yourself
Do it yourself is a term used to describe building, modifying, or repairing of something without the aid of experts or professionals...

) projection systems. The basic technique is to combine a high color-rendering index (CRI) high-intensity discharge lamp
High-intensity discharge lamp
High-intensity discharge lamps are a type of electrical lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. This tube is filled with both gas and metal salts. The gas facilitates the...

 (HID lamp) and ballast
Electrical ballast
An electrical ballast is a device intended to limit the amount of current in an electric circuit. A familiar and widely used example is the inductive ballast used in fluorescent lamps, to limit the current through the tube, which would otherwise rise to destructive levels due to the tube's...

 with a condenser and collector Fresnel lens
Fresnel lens
A Fresnel lens is a type of lens originally developed by French physicist Augustin-Jean Fresnel for lighthouses.The design allows the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a lens of conventional design...

, an LCD removed from a common computer display and a triplet lens
Triplet lens
A triplet lens is an optical device consisting of three single lenses. The triplet design is the simplest to give the required number of degrees of freedom to allow the lens designer to overcome all Seidel aberrations....


See also

  • Comparison of display technology
    Comparison of display technology
    This is a comparison of various properties of different display technologies.- General characteristics :- Temporal characteristics :Different display technologies have vastly different temporal characteristics, leading to claimed perceptual differences for motion, flicker, etc.The figure shows a...

  • CRT projector
    CRT projector
    A CRT projector is a video projector that uses a small, high-brightness CRT as the image generating element. The image is then focused and enlarged onto a screen using a lens kept in front of the CRT face. Most modern CRT projectors are color and have three separate CRTs , and their own lenses to...

  • Handheld projector
    Handheld projector
    A Handheld projector is an emerging technology that applies the use of an image projector in a handheld device...

  • Movie projector
    Movie projector
    A movie projector is an opto-mechanical device for displaying moving pictures by projecting them on a projection screen. Most of the optical and mechanical elements, except for the illumination and sound devices, are present in movie cameras.-Physiology:...

External links

Further reading

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.... }}
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