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Definition: rear-projection TV

An earlier large-screen TV that employed several technologies to generate the image. Rear-projection TVs (RPTVs) were developed to extend the size of the CRT TV, which for practical purposes maxed out at 36" (larger units weighed several hundred pounds).

Introduced in the 1970s and very popular throughout the 1980s and 1990s, at the end of 2012, Mitsubishi, the only remaining vendor of RPTVs, ceased production of its DLP-based 82" and 92" sets (for a novel rear-projection device, see SPUD).

Although RPTVs were bulky, no CRT TV could have been built with as large a screen. Using mirrors and lenses, the projected image was flipped up and over rather than straight toward the screen.

The Largest Screen for the Money
Early rear-projection systems suffered from a narrow viewing angle. Because the screen itself was a lens, standing up or walking off to the side dramatically changed the brightness. Although newer sets had wider viewing angles and were the only large-screen TVs available for many years, they were nowhere near the quality of today's LED and OLED TVs. See viewing angle, microdisplay, plasma, LED TV, OLED and video/TV history.

Rear Screen vs. Front Screen
Rear-projection systems were self-contained, whereas front-projection systems require a separate screen. Like regular TVs, RPTVs had a fixed screen size, whereas front projectors can change their screen dimension by changing the external screen and repositioning the unit (see front-projection TV).

It Started With Three CRT Guns
The first RPTVs used three 7" CRTs to generate red, green and blue light. This 64" set was two feet deep. A CRT TV with a 64" screen would have been too costly and too big to transport.

Liquid Crystal Microdisplays (MicroLCDs)
RPTVs were less bulky when microdisplays replaced the CRTs. Light was beamed through tiny red, green and blue LCD panels approximately 1.5" diagonal, each modulated with the pixel pattern for that color. Lenses enlarged the image. Another method was Liquid Crystal over Silicon (see LCoS).

Digital Light Processing (DLP)
DLP reflects light from tiny pixel-sized mirrors. Also used in today's front-projection units, the technology uses either a single chip and color wheel (this example) or three chips with their own sets of mirrors and color filters. See DLP.