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Developments in LCD Panel Display Technology

New HDTV LCD Flat-Panel Displays
improved CCFL, LED LCD TVs, Color Sequential technology...

LCD Panel Technology is constantly evolving in all areas from developments in the use of different liquid crystals and improved backlight technology for improved picture performance, to manufacturing processes that help improve the yield factor and therefore, reduce costs.

In this short article, we discuss the latest developments as applicable to LCD television. We also explore what major LCD flat-panel manufactures are doing to come up with LCD TV sets that are better, sharper, larger, and cheaper!

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Updated on: 25^th May 2009

Samsung LN52B750 52-inch
240Hz with gray 'Touch of Color'

Best-selling 52-inch 1080p LCD TV from the 2009 Samsung Lineup

New Technological Developments in LCD TV Applications

LCD panel technology is without doubt the fastest growing video display technology in the field of television and home entertainment.

This is not to say that technological advancements are not taking place in other flat-panel display technologies - in particular plasma, which in itself is the real major flat-panel competitor to LCD.

But in contrast, major developments in plasma displays have been moving at a slower pace and are taking place mainly to consolidate present-day technology.

In other words, the real technological break-through in flat-panel displays is taking place in the area of liquid crystal displays.

LCD panels today employ several variations of liquid crystal technology, including super twisted nematics (STN), dual scan twisted nematics (DSTN), ferroelectric liquid crystal (FLC) and surface stabilized ferroelectric liquid crystal (SSFLC).

Use of special plastics instead of the glass substrates, and flexible backplanes for flexible displays for use in specialized applications, has also become a reality.

The truth is that development in LCD flat-panel technology is coming from all fronts and from all major LCD panel manufactures. This is leading to larger displays panels, improved response times, higher resolution, faster refresh rates, better color freedom, and equally important to the end-customer, cheaper LCD TV sets.

Price / Size issue in LCD Panels

Price and Display Size are both limited by the quality-control problems faced by display manufacturers. Increasing the display size implies adding more pixels and therefore more transistors - thus increasing the chance of including a few bad transistors in a display. This in turn will further increase the rejection level.

However, larger and cheaper is the way LCD HDTVs are heading. The latest developments in the manufacturing processes of LCD mean that price is no longer an issue when choosing between plasma and LCD display technology for anything up to 55-inch. We have already seen 50-inch LCD HDTVs selling at a similar price tag to that of corresponding plasma televisions. And at 55-inch, the price difference is just marginal and is more a result of the supported feature set rather than the display technology itself.

This is all thanks to the efforts invested during these last years by LCD panel manufactures in developing next-generation LCD production techniques aimed at improving yield at the larger 50 to 55-inch LCD panel size. Up to very recent, this TV screen size segment was considered the domain of plasma displays. This panel size is becoming the real favorite TV size in today's multi-billion dollar home entertainment market.

However, 55-inch is the real maximum you can get with LCDs today in that at larger screen sizes you do not have much of a choice. The few 65-inch models we are aware of all come from Sharp, with the most affordable of these being the 65-inch LC-65D64U ($3,200). At this screen size, plasma and yes... rear projection, still offer more choice; in particular, rear projection is still available for those who want a massive 70-inch plus lamp-based display at under $2000.

Mind you, larger size LCD panels are available - though not as a mass-market solution. As early as 2005/2006, both Samsung and Sony exhibited large 82-inch TFT-LCD TV prototypes at the IFA 2005 and CES 2006 shows. And in June last year, Sharp Corporation came up with a monstrous 108-inch LCD monitor for business and commercial applications - the LB-1085.

Developments in LCD Backlight Technology

Advancement in backlight technology aimed mainly at improved picture quality, improved motion resolution, and improved energy efficiency of LCD panel displays is another area where we are seeing a lot of investment, with different manufacturers proposing different backlight solutions.

Main developments include:

	Improved Fluorescent Backlights
	LED Backlights - 'Local Dimming' and 'Edge-Lighting'
	Color Field Sequential Technology

Improved Fluorescent Backlights in LCD Panels:

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 (CCFL) to power some of its flat-panel 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 - using a proprietary 4-color fluorescent backlight - through the addition of a 'crimson' emitter to the traditional red, green, and blue (RGB) cold cathode fluorescent lamp light sources.

Sharp has added this fourth color to add more expression in the red range as research shows that the eye is extremely sensitive to this color. This has substantially increased the color gamut from the typical 70% of the NTSC to close to 80%. Still far from the almost 100% possible with the use of LED based backlight technology, but Sharp's 4-color fluorescent backlight is substantially cheaper.

LED LCD 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. Samsung flagship 46-inch LN46A950 LED HDTV with local dimming LED technology is presently selling for $3,000; its 55-inch version is selling at $4,000. Similarly, Sony's equivalent, the 46-inch KDL-46XBR8 LED HDTV is selling at $3,300. Even more expensive is the 55-inch KDL-55XBR8, which at $4,900 is too expensive for a 55-inch LCD - irrespective of the fact that this is a flagship HDTV from a top brand using the latest cutting-edge LED backlight technology.

Almost a year down the line, these sets still represent the very best that LED-based lighting technology offers to-day - with performance that is exceptionally close to that of the best premium plasmas from Pioneer and Panasonic.

LED Local Dimming Technology Explained

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.

LED backlight as used in Samsung and LG LCD HDTVs

Sony Triluminos LED backlight technology using red, green, and blue LEDs

Interesting is that while all three LCD display manufacturers are using LED backlighting in their LCD HDTVs, yet there is a significant difference in the way Sony is employing the technology with respect to the other two manufactures. Samsung and LG make use of white light LEDs.

Instead, Sony is using 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.

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;
	reduced power consumption;
	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.

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.

Edge-Lit LED TV Technology:

The LED TVs released so far this year 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. 2009 Sets within this category include the 40-inch Sony Bravia KLV-40ZX1M LED TV and the Samsung 2009 LED TV lineup we recently reviewed on our site.

But these edge-lit LED TVs can never deliver the same level of picture quality as LED local dimming technology; when it comes to screen uniformity, side viewing discoloring, and background brightness, performance falls short of their high price tag.

One thing worth taking note here with respect to 2009 LED LCD TVs is that TV makers are referring to LED LCD HDTVs simply as LED TVs - without actually differentiating between 'local dimming LED light technology' and 'edge-lit LED technology.'

We believe that this is being done on purpose. For many non technically-minded consumers, LED lighting technology represents the latest cutting edge technology in HDTVs. This is correct. What is incorrect however is that this is leading many to equate expensive LED TVs with a great picture. This is not necessarily so. The reality is that there is a significant difference in picture performance between edge-lit LED TVs and LED TVs using LED local dimming technology.

Color Field Sequential Technology

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.

Optically Compensated Bend (OCB)

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.

For the latest LCD panel HDTV sets available on the market, we advise to visit the amazon storefront; the vast choice of products and the various buying options available from the different retailers featured on the amazon site are among the best online.

However, prior to any decision, we recommend to do some research of your own. In particular, look at what other customers had to say about their LCD HDTV following their purchase. This will give you extensive insight about the product of interest. A good starting point in this respect is the customer feedback posted on amazon.

You can search the amazon storefront without leaving our site by using the amazon search box below; your search results will appear here under.

Amazon.com Widgets

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