Rear-projection television

Rear-projection television (RPTV) is a type of large-screen television display technology. Until approximately 2006, most of the relatively affordable consumer large screen TVs up to 100 in (250 cm) used rear-projection technology. A variation is a video projector, using similar technology, which projects onto a screen.

Three types of projection systems are used in projection TVs. CRT rear-projection TVs were the earliest, and while they were the first to exceed 40", they were also bulky and the picture was unclear at close range. Newer technologies include: DLP (reflective micromirror chip), LCD projectors, Laser TV and LCoS. They are capable of 1080p resolution, and examples include Sony's SXRD (Silicon X-tal Reflective Display), JVC's D-ILA (Digital Direct Drive Image Light Amplifier), and MicroDisplay Corporation's Liquid Fidelity.

Modern rear-projection television has been commercially available since the 1970s, but at that time could not match the image sharpness of a direct-view CRT. Current models are vastly improved, and offer a cost-effective HDTV large-screen display. While still thicker than LCD and plasma flat panels, modern rear-projection TVs have a smaller footprint than their predecessors. The latest models are light enough to be wall-mounted.

However, the projection technique is much older than this. Projection systems were used in the very early 1950s when it was still impossible to manufacture CRTs with a screen size much over 12 inches. Utilising a 2-inch monochrome CRT driven at a very high accelerating voltage for the size (typically 25 kV), the tube produced an extremely bright picture which was projected via a schmidt lens and mirror assembly onto a semi translucent screen of typically 17 to 19 inches in size. The resultant picture was darker than with a direct view CRT and had to be watched in subdued lighting. The degree to which the tube was driven meant that the tube had a relatively short life. Details of a specific TV set with its optical system can be found here.

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