SPECIAL FEATURE - Tv
SPECIAL FEATURE - Tv TECHNOLOGIES - LED THE LED PHENOMENON CONFUSION REIGNS PUBLIC AND INDUSTRY EDUCATION IS ESSENTIAL By Richard Barnes 47-inch slimmest LED TV modular type thickness of 8.9 mm, a courtesy of Bruc Berkoff Bruce Berkoff, Chairman of the LCD TV association and former EVP of LG.Philips LCD The rapid rise of LED technology as a key backlighting source for LCD TVs is creating a new buzz in the market, but is also creating confusion and misunderstanding. While several manufacturers are choosing to call LCD TV’s with LED backlight modules “LED TV”, both sales staff and public are finding it almost impossible to understand what it means. Is it really an LED TV? No… we just call it that way. It’s still really an LCD TV. In the following pages we aim not only to demystify the LED phenomenon, but also to put some figures on it and give you some solid projections. According to Dolby organisation, which is heavily involved in LED backlight development, the advantages of LED include: Friendlier to the environment: LEDs contain no mercury and have a long lifespan; Faster response time than CCFLs; Increased colour gamut with RGB LEDs; Projected exponential increases in efficiencies, in terms of lumens per watt; Declining costs, in terms of dollar per lumen per watt. LED technical improvements and cost reductions are likely to continue, because demand from other industries for instance, advanced automotive headlight and taillight systems is expected to drive increased production capacity and efficiencies. THE ExPERT’S POINT OF vIEw… To find out more, we spoke with one of the world’s “gurus” in the field of LCD technology, Bruce Berkoff, Chairman of the LCD TV association and former EVP of LG.Philips LCD (still on the board of LG Display), to tell us more… The most important part of an LCD display really is the light source and how you can control that light source. LED’s are the first DIGITAL light source for digital LCD displays. So this gives you a unique ability to use a more efficient light producer which leads to more energy efficient displays, as well as controlling digitally the light, which also leads to better black levels and contrast. It’s better for motion images as well. You can, for example, turn on and off the LEDs very quickly, with a strobe effect, to create image enhancements. This controls the average light level very quickly and improves motion blur, as well as allowing for regional or local area dimming. This gives better image quality, better perceived motion performance and lower power consumption. There are different kinds of LED backlights coloured, white, edge lit and direct lit… what are the trends? The differences have been overstated and there should be less and less difference over time. By far the majority are white LEDs now. You don’t generally need red, green and blue LEDs unless you’re looking for particularly high colour space. This is however generally not justified by the cost of these units, although this may improve over time. White LEDs are sufficient for the benefits in terms of local area dimming, and even the colour space and energy efficiency and black levels. However I think it’s overblown to talk about the difference between edge lit and direct lit, because one also should consider the number of parts. Edge lit models use far fewer parts, just like in notebooks. For direct backlit models, you need hundreds more LEDs. I believe the trend will be towards thinner, lighter edge lit systems, or even tiled systems, where you can cover the whole back plate with tiled edge-lit pieces having the cost benefit of being edge lit, but also the benefits of regional dimming throughout the whole display space. The bad news at the moment is it costs more, so the pressure is on to find ways to integrate solutions so you can save system level costs. Are LCD displays more eco-friendly using LED backlighting? Absolutely. The only minute dangerous chemical at all involved in any LCD display, which is the safest display… is the mercury used in the CCFL backlight, so LED’s make LCD even safer, cleaner and greener. People like Corning have already done an incredible job of getting the heavy metals out of the glass, and Merck have made a great job making the liquid crystals themselves safe, so now the final stage is cleaning up the backlights. How long will it take until the real crossover happens to LED backlighting? It will take a while. It’s the “S-curve” effect, but it could take three to five years until most LCD TVs have LED backlighting. 14 www.ifa-international.org IFA International • Saturday, 5 th & Sunday, 6 th September 2009
SPECIAL FEATURE - TV TECHNOLOGIES THE WHyS ANd WHEREFORES OF LEd BACkLIGHTING MEkO’S BOB RAIkES ExPLAINS THE TECHNICAL ANd FINANCIAL ASPECTS One of the 'hot' (in more ways than one!) topics of the last couple of years in the LCD business has been the question of backlight technology, especially the use of LEDs. LCDs are basically very inefficient displays. The 'cell' of the LCD doesn't create light, but just filters light from a backlight to create an image, and the efficiency is typically just around 5% or so. 95% of the light coming from the backlight is wasted. That means that backlight design and performance is a critical part of the energy consumption of a TV. Furthermore, the backlight represents around 40% of the cost of the LCD, so the LCD makers care a lot about the cost of that part of the display. Finally, the challenge for LCD makers in visual quality is to get contrast. Many outside the display industry think that the difficulty in making displays is to generate a bright white, but the reality is that in LCDs and PDPs, the challenge is to make a really dark black. Having a very bright backlight adds to the challenge for LCD makers. Traditionally, backlights for LCDs have been made using cold cathode fluorescent lamps - very small versions of the kind of lamps used for office lighting. CCFLs have been used because they have been one of the most efficient white light sources. However, they are fundamentally digital devices - they are either on or off so it is relatively difficult to control the level of brightness. Just as the world is moving away from traditional lighting sources, the LCD makers have identified LEDs as a potential replacement light source for backlights. Early experiments were with separate red, green and blue (RGB) devices which allow fantastic control of both the overall level of light across the screen and also the colour quality. However, controlling the devices is complicated and expensive and the cost of LEDs is basically proportional to the quantity, so this approach is only still being maintained in very high end sets, such as the top of the range from Sharp. White LEDs are more economical and can be used in two configurations. In one design, the LEDs are set on the edges of the LCD panel and light is passed through the LCD using a light guide. This kind of design makes extremely thin TVs possible and is the way that notebook LCDs are made. However, having the LEDs at the edge makes it hard to control the illumination on different parts of the screen. Direct-lit LED backlights put the LEDs directly behind the LCD. By controlling the brightness of individual LEDs, the backlight can be adjusted so that darker parts of the image have lower illumination and brighter parts have more. The technique is known as 'local dimming'. The technology has a huge advantage in improving contrast and the levels of contrast claimed by set makers at this IFA (from 3,000,000 to 1 to 5,000,000:1) are at the limits of what can be measured. The eye, anyway cannot see much above 100,000:1 at one time, so contrast above that is 'good enough'. The control of the backlight brightness also makes a big difference to energy saving. While PC users often have displays with large areas of white on the screen, the reality is that the average brightness of video content is between 15% and 30% of maximum, with most movies at the low end. If the brightness of the backlight reflects this lower power, the overall power efficiency can be much higher - a great advantage to everyone. The lower power reduces costs, makes the engineering of the backlights easier (the LEDs get very hot), reduces customers power bills and helps the environment. The use of LEDs also means the avoidance of the mercury Samsung "LED TV" - Hall 20 / Stand 101 that is essential to making CCFLs efficient. At the moment, LED-backlit sets cost more than CCFLbased sets, but LEDs are chips and follow Haitz's law (not dissimilar to Moore's Law) and typically double in brightness every 18 months. As a result, LED sets will increasingly become the mainstream of TVs in the next few years. PDPs don't have the backlights like LCDs, and have the potential to be slim (like edge-lit LED LCD TVs) and have high contrast (like locally dimmed direct-lit TVs) at the same time. But LCD is catching up fast! IFA International • Saturday, 5 th & Sunday, 6 th September 2009 www.ifa-international.org 15
