Developments in LCD Panel Technology

LCD is the display technology of choice in the HDTV market. This is no surprise; LCD panel technology is without doubt the fastest growing display technology in the field of home entertainment.

This is not to say that technological advancements are not taking place in other display technologies. Suffice to mention plasma—the only real competitor to LCD. But developments in plasma display technology, while consistent, are mainly addressed to consolidate the technology, with new displays capable of improved picture quality, reduced power consumption and reduced panel profile.

Some may point to OLED; it is true that during CES2012 we have seen the first 55-inch OLED HDTVs that will hit the market sometime later during this year. But OLED technology has still to prove itself and OLED HDTVs will for the time being, be expensive beasts.

In other words, the real technological break-through that literally changed the home entertainment market is LCD panel technology - mainly thanks to the developments 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, have also become a reality.

The truth is that development in LCD flat-panel technology is coming from all fronts and from all major display 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 and LED TV prices.

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 switching 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 and especially LED LCD TVs are heading. The latest developments in the manufacturing processes of LCD panels mean that price is practically no longer an issue when choosing between plasma and LCD display technology for anything less than 55-inch. We have already seen 46-inch LCD HDTVs selling at a similar price to that of corresponding plasma televisions. And at 55-inch, the price difference is just marginal and 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 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―though readily available―plasma starts to enjoy a significant price advantage over LCD HDTVs. The 55-inch flagship Samsung UN55D8000 LED LCD TV is selling at amazon for under $2,000, almost $1,500 less than its bigger 65-inch brother; this represents a 75% increase in price for less than 40% increase in display area! This price difference mainly arise out of the fact that at the larger screen sizes, your only real LCD TV option is the more expensive LED LCD TV; TV makers are limiting their cheaper CCFL LCD TV lineups up to 46-inch.

Though CCFL LCD TVs may be seen by many as a dying breed as more TV makers are channeling their development effort towards LED TVs, CCFL LCDs still have a lot to offer. The developments that took place in CCFL before the LED TV invasion eventually served as the basis for LED LCD TVs. In particular, the use of intelligence in the control of backlights is being put to a great effect in LED backlight systems employing some form of zone dimming functionality.

It was Philips who originally employed the use of intelligence in the control of 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 and the latest 480Hz panel refresh rates. This higher refresh rate comes into play with dejudder processing. It also 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 produce deeper black levels.

Samsung was the first to introduce the use of flat fluorescent lamp (FFL) instead of the standard cold cathode fluorescent tubular lights to power some of their flat-panel CCFL LCD HDTVs. The main advantage is that FFLs have a paper-thin form factor that produces light from its entire surface, thus rendering greater picture uniformity, better brightness, and a higher contrast ratio.

Sharp is also utilizing improved CCFL technology in their LCD panels. However, of particular interest with respect to Sharp is the enhanced color filtering at the sub-pixel level used by Sharp Quattron technology. The latter makes use of a fourth color—yellow—in addition to the standard red, green, and blue. The main benefit is a wider color gamut for a more true to life colors.

LED LCD HDTVs:

Surely, one of the main developments in backlight technology is the use of light emitting diodes or LEDs as a backlight source in LCD panels. As we will explain further on in this article, LED LCD TVs use one of two main backlight systems—edge-lit or full array with local dimming. However, since 2010, we started seeing a hybrid of these two technologies that aims at enjoying the pros of both.

LED backlights in LCD panels offer a few significant advantages over conventional CCFL backlight systems like reduced power consumption and the ability to dim the backlight in synchronization with the average brightness level of the content being displayed on the screen; the latter is partly the reason behind the much touted mega contrast ratio levels by LED TV makers.

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 in late 2008, both released the first LED TVs using full LED array backlights with local dimming. 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 and full array LED backlights in LCD panels has so far proved to be expensive to manufacture. For this reason, some TV makers started moving away from 'full LED array with local dimming technology and instead focus on the use of a hybrid LED technology; the latter uses zone dimming with edge-lit LED backlighting. In 2010, Samsung referred to this backlight technology as 'precision' dimming' technology; for 2011, the newly assigned Samsung name is Micro-Dimming Plus.

Despite the name, precision dimming—or micro-dimming—is not superior to backlight systems using full LED array with local dimming; but it is definitely better than standard edge-lit LED backlight technology as it introduces the ability to dim selected picture zones for improved black level performance over standard 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 average brightness level of the picture content within the respective screen segments they control, and

[2] The use of a special diffusion layer technology 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 zone dimming technology results in improved picture performance over standard edge-LED backlighting while still retaining the main advantages of edge-lit LED backlight technology over full array backlight systems, namely reduced power consumption, a slimmer panel profile, and affordability.

In addition, the latest micro-diming plus seems to have gone a step further in its ability to produce more precise zone control in LCD panels. A TV review appearing on Cnet for the Samsung D8000 LED TV show that this new technology is in effect truly capable of allowing for a more precise localized control of the backlight than the previous version, with the D8000 being capable of one of the very best TV pictures for the price.

But Samsung's Micro-Dimming Plus is not the only innovation in LED backlight technology... LG has also come up with improved LED TV technology for its high-end 55-inch 55LW9800 LED TV using full array LED backlight with local dimming.

Termed Nano LED technology, this is improved local-dimming LED technology in an ultra slim profile. In fact, LG Nano LED TVs come with a panel thickness that is more associated with edge-lit LED TVs than full array LED backlights with local dimming technology. At the same time, it also delivers improved picture quality with deeper localized blacks than that possible with an edge-lit LED backlight. LG Nano LED uses an extremely thin film printed with a proprietary light dispersion pattern combined with a full array of LEDs.

LG 55-inch 55LW9800 3D LED TV with Nano LED technology and Cinema 3D - defined by many as the best LG LED TV ever produced. (Available from amazon US)

This thin film incorporates tiny nano-size holes. The result is that LG's Nano LED technology produces a TV picture that is brighter and with significantly more uniform image brightness across the entire screen. Reviews show that the new LG flagship picture does not suffer from clouding or bleeding between different light zones, nor does it has any banding issues present on the LG LE8500 we reviewed in 2010.

LG's Nano LED technology is a derivative of the integrated optical plate (IOP) LED system introduced by LG in 2010 where LEDs were placed behind a special optical layer to enabled local diming. The aim was to create a slimmer LCD panel with full array of LEDs using local dimming technology. The result in 2010 was a relatively slim TV but not as slim as edge-lit LED TVs and the latest LG Nano LED TV.

LG's Nano LED technology advantage is not just the ultra slim LCD panel and improved brightness uniformity; it also uses an increased number of local dimming zones for improve picture quality and reduce blooming. The LG 55LW9800 utilizes 2,304 LEDs supporting 288 independent local dimming zones. In comparison, 2010 IOP 47-inch and 55-inch LED TVs utilized 864 and 1200 LEDs supporting 216 and 240 independently dimmable zones respectively.

LED Backlight Technology Explained

Full-array LED with Local Dimming

So far we have referred to LED local dimming without actually explaining why this is the best LED backlight technology ever produced so far for LCD panels.

The reason for its more precise control lies in the fact that this uses hundreds of LED modules 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. Local dimming LED backlight technology can achieve superior contrast performance to any other LCD backlight in use today.

LCD panel manufacturers using this technology have so far employed different backlight setups - with the most common being a full array of white LED lamps as used on some Samsung and LG LED HDTVs. Instead, Sony had originally made use of the Sony Triluminos Technology on its first LED TVs in 2008 whereby the basic LED backlight module consisted of three colors - using two green and one of each red and blue LEDs. According to Sony, this produces a wider color gamut with improved color purity.

It is not clear if Sony is still using this three-color LED backlight philosophy on the latest 2011 flagship Sony XBR-HX929 LED TV series; the XBR-H929 is Sony's latest LED TV series with full LED array using local dimming backlight technology. According to a Cnet review, the HX929 is one of best-rated HDTVs ever produced irrespective of display technology, with a superb picture worthy of a TV from a leader in the field. Its real drawback is its very expensive price for the screen size.

Edge-Lit LED TV Backlight Technology:

The majority of LED TVs released during these last years 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. This partly explains why edge-lit LED backlights does not really add anything to the TV picture quality but it definitely has its pros at well—in particular with respect to their inch-thick profile and ultra-low power consumption.

Edge-lit LED TVs—including Samsung's latest Micro-dimming plus—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 even though we have to admit that the latest LED TVs have shown significant improvements in these picture quality areas.