How A Projection TV Works
A rear projection television, often just referred to as a projection TV, is a type of large screen television. Most very large screen TVs, over 100 inches, use rear projection. As can be guessed by the name, the technology is related to a video projector, which projects onto a screen.
Rear projection TV technology has been commercially available since the 1970's, but few at that time could match the image sharpness of the conventional CRT. Current models have vastly improved, and offer an affordable HDTV large screen display. While still thicker than a LCD and plasma flat panel, modern projection TVs have a smaller "footprint" than their predecessors and are often light enough to be mounted on a living room wall.
A projection TV uses a projector to create a small image from a video signal and magnifies this image onto a viewable screen. The projector uses a bright beam of light and a system of lens to project the image to a much larger size. A front projection TV uses a projector that is separate from the screen, and the projector is placed in front of the screen, quite similar to a video projector or movie projector. The setup of a rear projection TV is in some ways similar to that of a traditional television, the projector is contained inside the television box and projects the image from behind the screen.
Three types of projection systems can be used in a projection TV. CRT projectors are the oldest, and while they were the first televisions to exceed 40", they were also quite bulky and the picture was unclear at close range. Newer technologies include DLP and LCD projectors. A type of LCD projection technology, LCoS, has been capable of producing 1080p resolution. Examples of these projection TV models include Sony's SXRD, JVC's D-ILA, and MicroDisplay's Liquid Fidelity. Today, the older CRT style projector and the more modern LCD projector are the two most popular styles of projection TV. In a CRT projector, small CRT's create the image in the same manner that a traditional CRT television does, which is by firing a beam of electrons onto a phosphor-coated screen. The CRT's can then be arranged in various ways. One arrangement is to use one tube and three phosphor coatings for the three primary colors: red, green, blue. Alternatively, one black and white tube can be used with a spinning color wheel. A third option is to use three CRT's, one for each color. With a LCD projection TV, a lamp transmits light through a small LCD chip made up of individual pixels to create an image. The LCD projector uses mirrors to take the light and create three separate color beams, which are then passed through three separate LCD panels. The liquid crystals are manipulated using electric current to control the amount of light allowed through. The lens system takes the three color beams and then projects the image.
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