Main developments include:Philips originally employed the use of intelligence in the control of the multiple high output fluorescent lamps operated in a scanning mode on some of their high-end LCD displays. This scanning principle is now being used by other TV makers like LG, Vizio, and Toshiba to generate blank frames in their 240Hz refresh rate dejudder processing. This helps cancel out the sample-and-hold effect, which is characteristic of conventional LCD technology. The end result is improved motion sharpness.Similarly, actively controlling the backlight brightness level in synchronization with the picture content helps improve gray scale performance and deeper black levels.Samsung is making use of a flat fluorescent lamp (FFL) instead of the standard cold cathode fluorescent tubular lights to power some of its flat-panel CCFL LCD HDTVs. The main advantage is that FFLs have a paper-thin form factor that produces light from its entire surface, offering the potential for greater picture uniformity, better brightness, and a higher contrast ratio. Sharp is also utilizing improved CCFL technology in their LCD panels - and enhanced color filtering at the sub-pixel level with the latest being Sharp Quattron technology whereby a fourth color - yellow - is being added to the conventional red, green, and blue. This has substantially increased the color gamut of respective Sharp LCDs - thus increasing the maximum number of colors to be displayed by these HDTVs.Surely, the most awaited devolvement in backlight technology has been the use of light emitting diodes or LEDs as a backlight source in LCD panels. LED backlights in LCDs offer a significant advantage over conventional CCFL lighting systems; individual groups of LEDs can be dimmed or switched off in synchronization with the average brightness level of the content being displayed on the screen. This leads to what is often being referred to by TV makers as mega dynamic contrast ratio levels.LG, Samsung, and Sony were the first LCD TV makers to come up with mass-market attempts at using LED backlit technology for their LCD HDTVs. In particular, both Samsung and Sony did leave their mark when late in 2008, both released the first LED TVs using local dimming LED backlights. These LED LCD TV sets did prove to be capable of superior black levels that are unsurpassed by a CCFL-based LCD - to the point that when displaying dark content in a completely darkened room, these sets literally disappear in the background.As expected, new technology does not come cheap. The latest LG LED TV with local dimming, the 55-inch 55LE8500 is selling online at under $2,500. Even more expensive is Samsung's latest flagship, the 55-inch UN55B8500 with full array local dimming LED technology which is presently selling online at $5,000.We say latest even though this was released almost a year ago. But for 2010, Samsung did not come up with full array local dimming but instead opted for what Samsung is calling 'Precision dimming technology on its high-end C8000-series and C6800 LED TVs. Despite its name, precision dimming is not superior to full array withy local dimming but it is definitely better than standard edge-lit LED backlight technology, this in view that it introduces the ability to dim selected areas on the screen for improved black level performance to these edge-lit LED TVs.
This is possible thanks to:[1] An LED edge lighting that is divided into different segments which can be dimmed independent of each other and in line with the brightness level of the picture content within the respective screen segments they control, and [2] The use of a special diffusion layer behind the LCD panel that directs light from the respective edge LED sections to selected segments on the screen surface.Samsung does not divulge how many unique screen segments the new technology can address but there is no doubt the new Samsung edge-lit LED backlight with precision dimming technology results in improved picture performance over standard edge-LED lighting.Hundreds of LEDs are placed behind the screen to replace the standard CCFL backlight used in LCD panels. Individual groups of LEDs are dimmed or switched off depending on the image content. It is this 'local dimming' technology that is behind the mega contrast ratio claims by the respective display manufacturers for their LED LCD HDTVs.
Interesting is that while all three LCD display manufacturers are using LED backlighting in their LCD HDTVs, yet there is significant difference in the way Sony employed this technology with respect to the other two manufactures when the first LED TVs appear in 2008. Samsung and LG make use of white light LEDs. Instead, on the extremely successful XBR8 series released in 2008, Sony used a three color led-based system using multiple LED units. Termed 'Sony Triluminos', each LED unit consists of two green LEDs, one red, and one blue. According to Sony, this produces a wider color gamut with improved color purity. It is not clear if Sony is still making use of this same technology in its latest 2010 HX909 series LED TVs - which is the only Sony LED TV series using full LED array with local dimming for 2010.LED backlighting enjoys a number of advantages over LCD panels using cold-cathode fluorescent lamps (CCFL), with the most significant being:
improved picture performance that is similar to CRTs with extremely deep blacks and impressive dynamic contrast ratings;
longer life that is typical twice that of CCFL based models;
in the case of LED backlights such as the Sony Triluminos using separate red, green, and blue LEDs, it is possible to get improved color rendering that is more true to life. Using separate color LED light sources to produce the three different primary colors gives a finer control over the exact light frequencies required to produce the three primary colors.Nothing is perfect! The way local dimming LED backlight LCD panel technology is presently being implemented by major TV display manufactures means that the 1000 or so individual LEDs used in these backlight systems are far from enough to correspond to the individual pixels forming the image. This means that local dimming LED light technology - no matter how selective it is - can never correspond to the exact requirements of the individual pixels forming the image. In other words, local dimming, while responsible for the extreme black levels of LED LCD TVs, yet it also produces a sort of a subtle halo effect instead of pure blackness in dark areas adjacent to bright parts of an image. This is due to light spilling over from light to adjacent dark areas in the image. Some refer to this as 'blooming' as a result of the way dark pixels at the edges of a dark object adjacent to bright objects appear brightened as well.Another issue that appears to be common among all LED LCD HDTVs and that emerged in all LED LCD HDTV reviews we encountered so far, is that their picture deteriorates at a much faster rate with off-angle viewing than in the case of LCD panels using standard backlight systems. The deterioration is such that even moving just a single seat on either side of the optimum center viewing position leads to washed-out colors and a worsening of the halo effect already referred to above.The majority of LED TVs released during 2010 use LED edge-lit LCD panel technology - a less complex derivative of LED lighting technology than local dimming. Simplistically speaking, these inch-thick edge-lit LED TV sets are nothing more than standard LCD TVs with LED (light emitting diodes) as their light source instead of CCFL. It has its pros as well - in particular with respect to their inch-thick profile and ultra-low power consumption. But edge-lit LED TVs - including Samsung's latest precision dimming - can never deliver the same level of picture quality as full array LED local dimming technology. Screen brightness uniformity and side viewing discoloring due to a restricted viewing angle are the main culprits here. leading to a performance that falls short of their high price.Directly related with tri-color LED backlighting, is 'color sequential'. Color sequential is becoming popular as a method of eliminating the color filters in LCDs. In 30 to 40 inch LCD panels, the color filter accounts for some 25% of the total cost of the LCD display panel. Thus, eliminating the color filters represents a significant way of reducing costs and simplifying the production process.Color sequential requires that a backlight emits red, green and blue light in sequence with one color at a time as required by the display content. This is somewhat similar to the color wheel process used in DLP-based projection systems (more info on the use of the color wheel in projection TV based systems is available in our Projection Television: How-it-Works guide).The LCD controller in a color sequential system is synchronized with the backlight so that when a given color backlight is on, only the matching color sub-pixels in the LCD are turned on. This would result in improved color gamut that is close to 100% of the NTSC gamut; this contrasts with the typical less than 80% of NTSC gamut achievable through the use of standard tubular CCFL backlight LCD displays. The end result is color that is much richer and more realistic.Eliminating the color filters in LCD panels has a further advantage. Red, green, and blue color filters used on sub-pixels absorb up to some 70% of light output from the backlight - thus eliminating the color filters implies that it is possible to use a lower brightness light source to achieve the same display brightness level. The end result is a significant reduction in power consumption.Yet, there is more in favor of color sequential backlighting. The use of color sequential technology eliminates the need for color sub-pixels; instead, the LCD panel can be redesigned so that it has three times as many regular pixels. In effect, each sub-pixel will become a pixel, which means that the resolution can be increased by a factor of 3.The LCD controller is still synchronized with the backlight; when a given color backlight is on, each pixel is set to the correct value for that color in the image. The eyes will see a rapidly changing sequence of red-green-blue images - (again, similar to a single chip DLP projection set-up); the brain will then combines these red, green, and blue monochrome images into a full-color image.It is interesting to note that this increase in LCD panel display resolution is achieved without increasing the risk of a higher level of bad pixels from that resulting from present display technology. This is possible since the increase in display resolution is being achieved not through an increase in the number of transistors on the display surface, but rather through re-design of the sub-pixel elements for these to operate as main pixels.Toshiba was the original display manufacturer that worked on Optically Compensated Bend (OCB) liquid crystals, with work mainly directed towards the development of small LCD panels for automotive applications.Up to very recent, a typical problem associated with standard LCD panels was the deterioration of the image as one moves away from the supported field of view. A lot of improvement has been going on in this direction. Most of today's LCD TV set support 170 degrees both horizontally and vertically. There are various ways that can help support a wider angle of view - Optically Compensated Bend is one of them.One side-benefit of OCB is that it makes the LCD inherently faster. Original tests by Toshiba had indicated a 3.3msec response time on their prototypes; this was at a time when the best LCD displays measured a typical 8 msec response time. Another interesting side-benefit of OCB is that it makes the LCD work much better in cold temperatures (-20C).The inherently faster response of OCB LCD panels makes these the ideal candidate for use with color field sequential technology. If color sequential is used to increase the resolution of the LCD, then a faster-responding LCD is needed because each pixel on the LCD panel is changing three times as often to display a rapid sequence of red, green, and blue images on the screen.If you are in the market for an LCD HDTV, we advise to visit the amazon storefront; the vast choice of products and the various buying options available from the different retailers are among the best online. However, prior to any decision, we recommend to do some research of your own. Look at what other customers had to say about their LCD following their purchase. This will give you extensive insight about the product of interest; a good starting point is the customer feedback posted on the amazon site. You can search the amazon storefront for LCD HDTVs without leaving our site by using the amazon search box below; your search results will appear here under.
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