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Choice Drakh
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Big Screen 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.

big screen television

Cathode ray tube technology was very limited in the early days of television. It relied on conventional glass blowing methods largely unchanged in centuries. Since the tube had to contain a very high vacuum, the glass was under considerable stress, together with the low deflection angle of CRTs of the era, the practical size of CRTs without increasing their depth was limited.[2] The largest practical tube that could be made that was capable of being mounted horizontally in a television cabinet of acceptable depth was around nine inches. Twelve inch tubes could be manufactured, but these were so long that they had to be mounted vertically and viewed via an angled mirror in the top of the cabinet. In 1936, the British government persuaded the British Broadcasting Corporation to launch a public high definition (for the era[a]) television broadcasting service.[b] The principal driver for the British government's move was to establish cathode ray tube production facilities which it believed would be vital if the anticipated World War 2 was to materialise.

The ability to correct the deflection signals for aberrations in tube geometry had not yet been developed, and it was necessary to make tubes that were relatively long compared with their screen size to minimise distortion. However, because the tube face had to be convex to provide resistance to air pressure, this mitigated the problem but only if the apparent deflection centre was more or less at the centre of curvature of the screen. This necessitated a tube that was relatively long for its screen size. The accelerating voltage used for these tubes was very low by later standards and even a twelve inch tube only ran from a 5000 volt supply. The early white phosphors were not as efficient as later offerings and these early televisions had to be watched in subdued lighting.

Unfortunately, both Philips and HMV had to withdraw their sets from exhibition by the afternoon of the first day as the cathode ray tubes had failed in both cases. Customers who had purchased these sets were disappointed to discover that their tubes rarely lasted longer than a few weeks (bearing in mind that there was only one hour of television broadcasting each day). By November 1937, Philips decided that it was more economic to buy the sets back rather than keep replacing tubes under warranty, which were becoming harder to source as the demand outstripped supply.[4][g] No information is available as to how HMV handled the problem.

By 1938, Philips had substantially overcome the shortcomings of the previous cathode ray tube to produce the Philips/Mullard MS11/1[h] projection tube.[5] This new tube was basically similar but had a larger cathode that required more heater power which was able to support a higher beam current.[i] This new tube retained the green phosphor screen of the earlier tube. The television set also had a smaller 21 inch screen which was roughly three quarters of the area of the previous year's model which meant that the tube did not have to be driven so hard. Purchasers of this later model only got to use it for a year or less as television broadcasting was suspended in 1939 for the duration of the Second World War. Both models of the television had a problem in that the high accelerating voltage on the tube meant that it produced substantial X-radiation. This was not widely looked at as a concern in the 1930s.[j] Fortunately most of this radiation passed through the bottom of the set from the downward pointing tube.

In the United States of America television broadcasting became more widespread at the end of the Second World War.[6][7] Although cathode ray tube technology had improved during the war such that tubes became shorter for their size, as it was now possible to correct distortions, twelve inches was still the practical limit on size. However, it was now possible to mount a twelve inch tube horizontally in an acceptable cabinet size. As a result of these size limitations, rear projection systems became popular[8][9] as a way of producing television sets with a screen size larger than 12 inches.[10] Using a 3 or 4 inch monochrome CRT driven at a very high accelerating voltage for the size (usually 25,000 volts[11] though RCA did produce a larger five inch tube that required 27,000 volts.[10]), the tube produced the extremely bright picture which was projected via a Schmidt lens and mirror assembly onto a semi translucent screen of typically 22.5 to 30 inches diagonal in size using an optical system practically identical to the earlier Philips system described above. The only change was that RCA used the optically superior convex screen on the tube having figured out that the Schmidt lens did not have to correct for the curvature of the tube face but only the spherical aberration of the mirror. The resultant picture was darker than with a direct view CRT and had to be watched in very subdued lighting. The degree to which the tube was driven meant that the tube had a relatively short life.

As the 1950s unfolded, there were several major advances in cathode ray tube technology. Pre stressing the bulb of the tube with steel bands around the outside of the screen for implosion protection allowed larger tube diameters to be produced. Improvements in correcting for deflection aberrations on those screens allowed larger deflection angles and consequently shorter tubes for a given screen size. Further: much simpler deflection systems had been developed that could generate the large currents required without consuming the power of earlier circuits. By 1956 the ability to produce near rectangular faced tubes was developed. This was facilitated by the pre stressing, but still required the walls to have a convex shape to withstand the atmospheric pressure.[14] Although 17 inches in size was the largest size at this time, it was large enough to render rear projection technology obsolete for the immediate future. Using the superior white phosphor of the post war period and higher accelerating voltages,[n] televisions were larger and brighter.

As television technology developed and picture quality improved, limitations in cathode ray tube sizes became an issue once again. Even though larger screen sizes with short tube lengths were available, there was a revival of interest in rear projection systems to achieve picture sizes that were beyond the capabilities of direct view cathode ray tubes of the time. Modern color rear-projection television had become commercially available in the 1970s,[15][16][17] but at that time could not match the image sharpness of a direct-view CRT.

While popular in the early 2000s as an alternative to more expensive LCD and plasma flat panels despite increased bulk, the falling price and improvements to LCDs led to Sony, Philips, Toshiba and Hitachi dropping rear-projection TVs from their lineup.[18][19] Samsung, Mitsubishi, ProScan, RCA, Panasonic and JVC exited the market later as LCD televisions became the standard.

Early RPTVs were essentially CRT projectors with a mirror to project onto a built-in screen. They were heavy, weighing up to 500 pounds.[25] The first RPTVs to not use CRTs were launched in 2002, using DLP, LCD and LcOS technologies, requiring a UHP lamp. UHP lamps used in projectors and RPTVs require periodic replacement, as they dim with use. The first wall-mountable RPTV was launched in 2003 by RCA. The first DLP 1080p RPTV was launched in 2005 by Mitsubishi. The first RPTV to use LEDs instead of an UHP lamp as its light source was released by Samsung in 2006. RPTVs that used a plasma lamp were released by Panasonic in 2007.[26][27] The first RPTV to use lasers instead of an UHP lamp or an LED was released by Mitsubishi as the LaserVue in 2008. Samsung exited the market by 2008, leaving Mitsubishi as the sole remaining manufacturer of RPTVs until it stopped in 2012 due to low profit margins and popularity.[28]

A projection television uses a projector to create a small image or video from a video signal and magnify this image onto a viewable screen. The projector uses a bright beam of light and a lens system to project the image to a much larger size. A front-projection television uses a projector that is separate from the screen and the projector is placed in front of the screen. The setup of a rear-projection television 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.

UST projectors are an extreme version of short-throw projectors. Traditional short-throw projectors like the one we recommend in our budget projector guide often look like big-lensed versions of their non-short-throw counterparts and are designed to fit the space in between UST and traditional projectors. If you imagine a traditional projector at the back of a room and a UST projector in the front next to the screen, a short-throw projector would be halfway between them. The exact distance varies, but generally a short-throw model is designed for placement on a coffee table between the couch and the wall or screen.

More affordable 1080p UST projectors, such as the Optoma GT5600, use DLP projection technology and a traditional lamp bulb to create the image, whereas more-expensive, 4K-friendly models, like the Epson LS500 or the Sony VPL-VZ1000ES, use LCD or LCoS technology and lasers as the light source. Companies such as Epson and Hisense also offer complete packages that pair their UST projectors with matching ambient-light-rejecting (ALR) screens, usually in a 100- or 120-inch size. These systems include everything you need to get up and running, taking the guesswork out of pairing a projector with a screen. (We discuss the importance of the screen below.) 041b061a72


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