A large-screen TV set that uses one of several technologies for generating the image. All methods yield larger screens than the one-tube, direct view CRT TV, which reached a practical limit around 36". The depth of rear screen sets is reasonably shallow because the image is projected through a series of lenses and mirrors that turn it toward the screen at the very end.
They Started with CRTs
The first rear projection sets used three CRT guns to generate red, green and blue light. Newer technologies use tiny microdisplay panels no more than an inch square, which result in even shallower sets, although not as thin as plasma or LCD displays.
A Lot of TV for the Money
Rear-projection systems have traditionally suffered from a narrower viewing angle than other displays including CRTs and flat panels. Because the viewing screen itself is a lens, standing up or moving off to the side changes the brightness of the image for the viewer. However, newer sets have wider viewing angles, and although not as visually dazzling as plasma TVs, rear-projection sets offer a competitive alternative at a far more affordable price.
Rear Vs. Front Projection
Although rear-projection TVs have screens as large as six feet (diagonal measurement), front-projection TVs can project a much larger image onto an external screen, and the image size can be changed by replacing the screen and/or repositioning the unit (see front-projection TV). See microdisplay, plasma, LCD and video/TV history.
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CRT-Based (The Original)
The first rear-projection technologies used three CRT guns to create red, green and blue images, which were mixed together. In order to generate sufficient light, the tubes were large, but the depth of 50" units was still only about two feet. Since CRT-based units use traditional phosphor tubes, they easily provide variable resolutions, whereas newer microdisplay-based use a fixed pixel matrix just like plasma and LCD displays. However, the microdisplay-based units use tiny imaging panels and fit into much narrower cases.
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LCD-Based Microdisplay (MicroLCD)
Light is beamed through three tiny LCD "microdisplay" panels (one red, one green, one blue) that are approximately 1.5" diagonal. Each microdisplay is modulated with the pixel pattern for that particular color. The image is enlarged to the size of the screen by a set of lenses.
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DLP and LCoS Microdisplays
DLP (Digital Light Processing) and LCoS (Liquid Crystal over Silicon) systems reflect light from tiny panels. DLP rotates pixel-sized mirrors to reflect light. LCoS uses LCD microdisplay panels similar to the LCD-based units mentioned above, except after passing through the microdisplays, the light is reflected from a mirror to the lenses. To generate color, DLP units either use a single chip and color wheel or three chips, each with its own set of mirrors and color filter. LCoS units use three LCoS panels. For more details, see DLP and LCoS.
Which Is Better?
Visual display technologies are rather subjective. To your eye, one type may look superior to another. The only way to know is to play your favorite types of movies on as many different TVs as you can. Otherwise, all the specifications in the world are meaningless.
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