NOV 2013 David Elien VP of Marketing & Business Development, Cree, Inc.
Let There Be
LIGHT How Cree reinvented the light bulb
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Cutting Edge Flatscreen Technologies
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New LED Filament Tower
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mensional array of LEDs behind the LCD may offer the ultimate performance for d TVs, the performance possible with panels (using LED light bars at the top/ or edges of the display) now provides nstream market solution, accounting for % of all LED backlit displays. And clearly ge-lit displays requiring far fewer LEDs irect backlight array, especially using the brightness LEDs now available, the cost is obvious.
CONTENTS
Lighting Electronics
TECH ARTICLE
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TECH ARTICLE
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COVER INTERVIEW
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PRODUCT HIGHLIGHT
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TECH ARTICLE
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How to Backlight LCD TV Dipslays With Scrolling LEDs
Taking Measurements of Single LEDs
Interview with David Elien Cree, Inc.
Cree’s Revolutionary LED Filament Tower Light Bulb
Cutting Edge Flatscreen Technologies
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Lighting Electronics
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TECH ARTICLE
By Girish Ramesh, Sr. Marketing Manager, Atmel Corporation and Kevin Hempson, Staff Applications Engineer, Atmel Corporation
I
n just a few years, LEDs have become the dominant technology for backlighting LCD displays for TVs and desktop monitors, consigning cold-cathode fluorescent tubes to history. The challenge now for manufacturers, as always, is optimizing designs to extract maximum performance for minimum cost. And this often comes down to what’s right for a particular application. So while direct LED backlighting, using a full two-dimensional array of LEDs behind the LCD panel, may offer the ultimate performance for high-end TVs, the performance possible with edge-lit panels (using LED light bars at the top/ bottom or edges of the display) now provides the mainstream market solution, accounting for over 90% of all LED backlit displays. And clearly with edge-lit displays requiring far fewer LEDs than a direct backlight array, especially using the higher-brightness LEDs now available, the cost benefit is obvious.
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Lighting Electronics
Scrolling is All About Timing
With LEDs able to illuminate more localized areas of the screen, and with their much faster response times, it becomes possible to dim the backlight in darker parts of the scene while retaining full brightness elsewhere in the same frame.
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The basic requirement for edge-lit panels is delivering a sufficiently bright backlight evenly across the entire LCD panel. With cold-cathode tubes, which were also placed along the edges of the display, this was achieved a combination of diffusers and polarizers. Having a row of LEDs at the edge of a display opens up other possibilities, allowing the light from individual LEDs to be directed to specific areas of the display (known as illumination zones). Additionally, although dimming a cold cathode backlight can provide enhanced contrast when viewing dark scenes, this was generally restricted to the whole screen, so at best only allows for frame-to-frame variation and more likely spills over to neighboring frames. With LEDs able to illuminate more localized areas of the screen, and with their much faster response times, it becomes possible to dim the backlight in darker parts of the scene while retaining full brightness elsewhere in the same frame.
TECH ARTICLE
Figure 1: Pixel settling time after writing data The secret to all of this lies in the timing of the illumination, delivering the light to the screen at precisely the right time, in synchronism with the displayed image and allowing for the characteristics of the LCD itself and any losses in the optical components. The solution is broadly referred to as a ‘scrolling backlight system’ but employs a number of techniques to realize a superior picture all of which are made possible by sophisticated LED driver technology, such as that embodied in Atmel’s MSL2164 series devices. This article will reveal how this works in principle with the help of some timing diagrams and a description of the different modes of operation. Let’s start with a commonly used method for overcoming one of the fundamental issues with LCDs; namely the slow response time of the liquid crystal material, which gives rise to the problem of motion blur where on-screen movement is faster than the time it takes for the pixel to settle to a new value. This can be greatly improved by blinking or interrupting the backlight during the period while the pixel is changing. Commonly referred to as ‘black
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Lighting Electronics frame insertion’ (a confusing expression since with LEDs the backlight is only turned off during part of the frame and not for a whole frame as used to be the case with cold cathode tubes), this technique works particularly well in conjunction with illumination zones because the whole screen is not blanked at the same time. For example, If we take an HDTV with 1080 rows of pixels edge-lit with just eight LEDs we get eight horizontal illumination zones each containing 135 rows of pixels. As the LCD image is built up by writing one whole row of pixels at a time, we can see from figure 1 that there is a significant delay, referred to as the ‘phase delay’, after the vertical sync pulse (PHI) before all the pixels in Zone 1 (rows 1-135) are fully settled. Clearly the optimum time for viewing this zone is once the pixels are settled so ideally we only want to illuminate this zone during that period. For subsequent zones (zones 2 – 8) the optimum viewing/illumination period will be similarly offset by the phase delay from the start of that zone’s pixel writing period i.e. staggered throughout the frame, resulting in the illumination scrolling down the display.
Figure 2: Reverse PWM avoids next pixel writing period
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Another limitation of LCDs with constant and uniform backlighting is their limited contrast range. This is because an LCD pixel is not a perfect shutter so even in its dark state there is some light leakage, especially when the panel is viewed at an angle. As noted earlier, contrast enhancement is possible by dimming the backlight for dark scenes, but the advantage when combined with scrolling LED backlights is being able to control the brightness during the illumination period. Also, the accuracy of addressing each frame and zone independently allows a much faster response to dark-to-bright scene transitions than is possible with non-scrolling backlights.
TECH ARTICLE
The method for adjusting brightness during the fully settled pixel period is simply by varying the amount of time the backlight is switched on during that period – a method more generally termed ‘pulsewidth modulation’ or PWM. Typically, there would be a default brightness level, with an associated PWM illumination period value, that is less than the full period during which the pixels are stable; this allows for higher or lower brightness levels by setting larger or smaller PWM values. Conventional PWM dimming turns the backlight on at the start of the stable pixel period and off after the PWM illumination period. But, as can be seen in Figure 2, there is a danger that a large PWM value may result in the backlight remaining on into the next pixel-writing period for that particular illumination zone (area A), which is clearly undesirable. To overcome this problem the Reverse PWM method aligns the end of the PWM period to the end of the fully settled pixel period as can be seen at the bottom of Figure 2 since it is better to always use area B and to start the illumination as early as necessary to achieve the desired brightness.
LED backlighting for LCD TVs using edge-lit display panels has rapidly become the technology of choice, providing both a highperformance and costeffective solution for the majority of the TV and desktop monitor market.
One point to note is the importance of referencing the timing of all illumination zones to the same V Sync that is associated with the start of that frame’s pixel writing process. Referencing some zones to a subsequent V Sync can result in brightness banding because of variations in frame duration that can result from video manipulation.
Conclusion LED backlighting for LCD TVs using edgelit display panels has rapidly become the technology of choice, providing both a high-performance and costeffective solution for the majority of the TV and desktop monitor market. The faster switching speed of LEDs coupled with advances in driver circuit design makes it possible to address some of the previous limitations of liquid crystal displays, namely motion blur and poor contrast. ■
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Lighting Electronics
Measuring S Alan Lowne, CEO Saelig Co. Inc.
Pocket-sized precise LED measurement s With the advent of high-brightness blue and white LEDs, the market for LED light has been growing exponentially. LEDs are used in displays, illuminated advertisements, lamps, and throughout automobiles. LEDs are found in light fixtures, aircraft, traffic lights, and theater, photographic, and architectural lighting. But is impossible for LEDs to be manufactured with identical spectral properties due to the variations in production processes, physical housings, and operating conditions. Brightness and color peak can vary substantially from
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TECH ARTICLE
Single LEDs
solution offers laboratory-grade precision component to component even in the same production batch. For critical applications (not merely indicator lights) LEDs need accurate testing methods during manufacture and in final assemblies. Precise optical characterization is also valuable in research situations for LED-based products, or for batching or “binning� LEDs (i.e. selection of color and brightness groups) with nearly-identical characteristics for assembly lines.
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Lighting Electronics
Full-color LED displays contain many thousands of LEDs, and their illumination characteristics need to be matched to ensure good color uniformity. Measuring single LED performance may also be necessary once they have been installed on a PCB. Quality control of incoming LEDs delivered by different suppliers may be needed for binning, or for characterizing fiber optic sources like endoscopes, or even calibrating lighting fixtures made of many LEDs. Other applications for LED testing include investigating the influence of dimming, testing diffusers or optics installed on LEDs, monitoring changes of spectra, color or luminous flux due to current drive, time, or temperature. Uniform luminance and color in automobile cockpits is also very important, requiring color matching various sub-assemblies and modules from different suppliers. Full-color LED displays contain many thousands of LEDs, and their illumination characteristics need to be matched to ensure good color uniformity. Other applications include LED-based measuring instruments such as blood analyzers that determine blood-sugar concentration. Precise characterization of LEDs in these applications is critical since this affects the life-saving accuracy of the results.
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Measurements Typical measurements can include: Lumens (luminous flux), CCT (correlated color temperature according to CIE standards), CRI (color rendering index according to CIE standards), COLOR (color coordinates according to CIE 1931 and CIE 1964), and mWatt (radiant power value). One very useful highly portable solution that offers the accuracy of benchtop instruments is the combination of the GL SPECTIS 1.0 and the GL OPTI SPHERE 48. Ready to run within 10 seconds of connecting this handheld plug ’n’ play combo to a computer, the system automatically detects which accessories have been attached to it, and it is rapidly ready to perform measurements. Each instrument and accessory is provided with individual instrument calibration comes as standard to ensure that the results produced are correct and reliable. It is a portable solution that can be taken to the production line or packed in a travel bag for field use.
TECH ARTICLE
The GL SpectroSoft software included in the package is intuitive, user-friendly, delivers results within seconds, with the ability to easily export or import results or settings. Measurements include: CIEcompatible color coordinates, correlated color temperature, Color Peak, Color dominant, CRI color rendering index, MI metamerism index, color charts according to different CIE standards, etc. By default, this mini-spectrometer measures from 340750 nm but the range can be reduced for measurements of particular light sources. The software includes a BIN EDITOR which helps to define a binning set, specifying individual fields on the chart with X Y values. Specific names and X1, Y1 X2, Y2, X3, Y3… values are assigned to these fields, which designate a specific rectangle on the chart. The most critical bin criteria that impact product performance are light output and color temperature. Binning for light output is very straightforward - LEDs are individually measured and sorted by lumen output into prescribed ranges. Luminaire manufacturers can easily select the bin or bins that best meet the lumen performance requirements of their fixture. Binning for color temperature is a more complex process. Color temperature bins are defined by (x,y) coordinates on the CIE 1931 Chromaticity Diagram (shown at right). These bins are grouped as quadrants around the standard chromaticity lines for a specified color temperature. For more information about color binning, bin sizes and the ANSI C78 377A, see: http://www. nema.org/media/pr/20080221a.cfm.
Summary GL SPECTIS 1.0 and the GL OPTI SPHERE 48 are a useful tool combination for manufacturers, production environments, field work, as well as laboratories in a range of real-world applications. ■
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Lighting Electronics
Out With the Old,
In With The New David Elien, VP of Marketing & Business Development, Cree, Inc.
Cree, Inc. is a market-leading innovator of LED lighting products, LED components, and semiconductor products. The company aims to make energy-wasting traditional lighting technologies obsolete through the use of energy-efficient, environmentally friendly LED lighting. In recent months, Cree has been leading the lighting revolution by unveiling its line of LED light bulbs for the consumer market. With its ENERGY STAR速 certification and commercial retailer in place, Cree hopes to achieve mass adoption of these LED bulbs to ensure energy efficiency and a greener future. We spoke with David Elien, VP of Marketing & Business Development at Cree, about Cree's innovative work environment, its brand new LED bulb, and how the company plans on getting on board with this revolutionary technology.
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COVER INTERVIEW
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Lighting Electronics
“ At Cree, our goal is to give the consumer a no-compromise solution. The only way people are going to transition to energy-saving alternative technologies is if consumers know LED lighting products work as well as, or better than the products they are already using.” Tell us about Cree’s latest products— what are you excited about what are you introducing into the market? Well, we’re introducing a lot of products. We have a long track record of innovation, and continue to deliver enhanced solutions that make it more rewarding and economical for consumers, businesses and entire cities to switch to LED. A product that people are talking about lately is our Cree LED Bulb. This is for a variety of reasons—one being that you can view it as a hallmark for the lighting industry. This is an LED bulb that looks like a bulb, lights like a bulb, but works much better than all the alternatives that are available to consumers. The Cree LED Bulb has served as a platform for us to introduce the Cree brand to a broad audience. The Cree LED Bulb is sold exclusively at The Home Depot. We just achieved ENERGY STAR® certification for the soft white Cree LED Bulb, making the bulb eligible for utility rebates throughout the country. It’s the industry’s first affordable LED bulb to look and light like an incandescent and achieve ENERGY STAR level of qualification.
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Being able to dim an LED light bulb like a traditional bulb is also a really appealing feature for a lot of customers. At Cree, our goal is to give the consumer a nocompromise solution. The only way people are going to transition to energy-saving alternative technologies is if consumers know LED lighting products work as well as, or better than the products they are already using. One of the rules we follow for every product launched, is that it has to deliver an as-good or better experience than what is being replaced, plus superior economics.
So what have been the greatest challenges in replacing traditional bulbs in the market? The biggest challenge was designing a bulb that looks like a bulb. In hindsight, it seems pretty straightforward. It’s because we created a solid plan. There is a lot of engineering that went into designing a bulb that looks and lights like an incandescent while leveraging all the great attributes of LED technology. I think the first thing to consider in designing an LED bulb
COVER INTERVIEW should be getting the aesthetic of the light right. In all of our research, we’ve inferred that one of the reasons our bulb is outselling every other bulb at The Home Depot is because it actually looks like an incandescent bulb; consumers associate form with function. If you’re going to position or market something as a replacement, then it makes it easier for the consumer to make that leap if your bulb actually looks like one. The second challenge was getting the cost right. It was critical for us to deliver a series of bulbs that could be below the $10 barrier. Again, there was a lot of engineering and strategic supply chain management to deliver a low-cost, no-compromise lighting alternative. One of the technical breakthroughs that enabled Cree to break the $10 threshold is our new Cree LED Filament Tower™ Technology. The Filament Tower is the Cree innovation that lets our LED bulb replicate the look and feel filament based traditional lights. The new bulbs showcases innovation across the entire system: LEDs, power supply, optics and system design.
With this LED technology, what differentiates it from the competing products on the market? The first and most obvious differentiator of the Cree LED Bulb is the form, which is the first thing the customer sees. Many other LED bulbs out there, frankly, look like a science project. They don’t look like something a consumer wants to use or can use in their home. Once we won from an aesthetic perspective, the consumer sees the phenomenal pricing of the bulb. We created the first incandescent bulb-quality LED bulb to launch under $10. With the recent ENERGY STAR qualification, in some markets, there will be instant rebates available that take the cost of the bulb to under $5. This price will be a major differentiator, coupling that with performance is the winning ticket. The other key differentiator is that it lights like a bulb. It’s omnidirectional—when you take it home, it gives the quality of light you are used to from an incandescent. You wouldn’t know the difference. The last feature to highlight is our industry-leading 10-year warranty. The customer doesn’t have to go out on a limb by adopting our technology; it’s affordable and backed by an outstanding warranty, limiting risk and compelling consumers to try.
What does it mean when you say the bulb is ENERGY STAR Rated? There are specifications around light distribution, reliability testing, CRI (Color Rendering Index) and overall efficiency. The ENERGY STAR Rating is there to protect the consumer. Consumers want to do the right thing and save energy and they have been bitten in the past by lighting solutions that have fallen woefully short of their expectations, such as compact fluorescent bulbs (CFLs). They have had poor experiences to the point where it has slowed their appetite for energy-efficient technology. So ENERGY STAR has set the standard to help prevent these poor experiences. Many utilities that offer rebates only allow t bulbs that are ENERGY STAR rated to be eligible. Our bulb is the first bulb that actually looks and acts like a bulb to achieve that certification.
What is the future of LED lighting? What kind of innovations are happening that will continue to push this technology forward? We are just beginning to scratch the surface of what’s possible in LED lighting. The LED lighting industry is very lightly penetrated—we’re talking less than 10 percent of installed lighting is using LED technology today. There’s a lot of innovation left and the key will be to continue to draw toward parity with current technologies in a wider array of applications. This means more than the A19 bulb, but BR30 bulbs, and more.
Cree’s New LED Bulb 17
Lighting Electronics We have a lot of activity, quite frankly, on the commercial side of Cree that’s driving LED adoption for businesses, governments and entire cities. Cree launched an industrychanging LED residential street light starting as low as $99 – making it more affordable than ever for cities, municipalities and utilities to convert to energy-efficient LED. In June 2013, we announced the breakthrough Cree UR Series LED upgrade kit for commercial buildings such as offices, with the potential to obsolete linear fluorescent lighting—saving more energy, providing better light and lasting twice as long as the 32-watt linear fluorescent lights it replaces. We tend to focus on the biggest problems that have the biggest impact in the shortest time. So when I talk about street lighting, this is aimed at replacing every streetlight that is out there today. With our XSPR LED streetlight, which is the $99 residential streetlight we launched, cities and municipalities can place the light where they want as LED is a directional light source. You’re working with discrete packets of light that you can shape and place where you want. Cree, as we solve some of these applications and look to create value, is developing some of those attributes and technologies.
Given the challenges of getting your product into more industries and tackling new markets what do you see as the greatest challenge in driving Cree forward? Getting the industry moving is our biggest challenge. We spend a lot of the time thinking about what we need to demonstrate to the industry, at an ever-increasing pace, that the technology is ready and they ought to want to jump in. In terms of the increasing competition; we invite that—we want it because it validates our strategy and that it’s working. Take the Cree LED Bulb for instance, we launched our bulb in March and in the last few months we’ve seen a flurry of announcements from a variety of manufacturers large and small, and retailers, that they finally have a $10 LED bulb or that they’re striving to be as good as ours. That’s a validation that we’re doing things to move the market. What we need to be careful of, is ensuring that the industry is accountable for delivering great products that will further
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move consumers toward adoption. So that’s our biggest challenge—how do we continue to innovate at a technical and commercial level and show that you can create substantial value for our consumers with our technology to get the market moving in the right direction.
Absolutely. That’s a big challenge, and that’s what keeps everybody moving. And one way to highlight that from a numbers perspective is that there are 5 billion sockets in the U.S. that use an Edison-like bulb and I can tell you we may be the best selling bulb at The Home Depot by a large measure, but it’s still early on in the market. Our goal is to drive 100 percent adoption of LED technology, so there’s a lot of opportunity.
What’s the company culture like at Cree? Cree, Inc. is a market-leading innovator of LED lighting products, LED components and semiconductor products, changing the way people use light. Our goal is to drive 100 percent adoption of LED lighting in order to obsolete energy-wasting technologies. Every day we come to work, our goal is to relentlessly innovate. The only way we’re going to change a century-old industry is to develop products that really change the game, compel consumers to try, and then deliver a positive experience. This will help drive some of the incumbents in the industry to shift toward LED technology at a faster pace than they would otherwise. Because of our mission, our culture is characterized by being very fast-paced, believing anything is possible with a mindset of continuous improvement. Even though we’ve achieved a lot, there’s always a way to do it better.
Is there a collaborative innovation process at Cree? We have a strong focus on teamwork here at Cree. No matter what the goal is, everyone has a role to play. If you interact with executives here and walk around, you’d see it’s very unassuming—it’s flat and there isn’t a lot of hierarchy or sense of entitlement with executives. For example, there are no reserved parking spaces. We have a very team-orientated culture.
COVER INTERVIEW
“ In terms of the increasing competition; we invite that—we want it because it validates our strategy and that it’s working.”
Above: Cree’s manufacturing facility in Durham, North Carolina
Where would you like to see the LED industry moving towards? We need to make sure as an industry that we’re driving toward a no-compromise solution—that we deliver in a lot of instances, however the industry has opportunities to do a lot better than it’s doing and consumers deserve better. As an industry, the emphasis ought to be on meeting or exceeding the current experience customers are getting with their light sources, and being really clear and thoughtful about the performance of your product. Anything short of that does a disservice to the consumer and it impedes the overall growth of the industry. I think consumers have had to put up with enough compromises, whether from CFL bulbs or LED bulbs that compromised function for cost. We have a real opportunity to deliver a solution that consumers can use and be happy with for decades. ◌
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Lighting Electronics
CREE LED Bulbs Compete With Incandescent and CFL Cree, Inc., the leading supplier of energy-efficient LED lighting products, broke the $10 price barrier with new LED A-type bulbs for the home—the Cree® LED Bulb. These bulbs are the ideal replacement for both traditional incandescent and CFL bulbs. The Cree’s soft white LED Bulbs are ENERGY STAR qualified, making the bulbs eligible for many utility rebates that could bring the cost of the products to under $5 in certain regions.
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PRODUCT HIGHLIGHT
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Lighting Electronics Cree LED Bulb vs. Incandescent The Cree LED Bulbs offer the size, shape, warm color temperature, and omnidirectional illumination of traditional incandescent bulbs while using 78% to 85% less energy and boasting a rated-lifetime of 25,000 hours. These new Cree LED Bulbs are available in six versions – including the new 93 CRI Cree TW Series LED Bulb – designed to replace 40 and 60 watt incandescent
a glass bulb. Cree calls this the Cree LED Filament Tower™. The Cree LED Filament Tower creates the same nuance and visual texture as a traditional incandescent bulb by emulating the compact light source of an incandescent filament Lighting Outside the Home LED lighting products are offered for nearly every application including residential, retail
Compared to incandescent bulbs, Cree LED Bulbs save the user energy, money, and time. bulbs while consuming only 6 to 13.5 watts. And they’re available in color temperatures of 2700 K (soft white) and 5000 K (daylight). Compared to incandescent bulbs, Cree LED Bulbs save the user energy, money, and time. For example - compared to an incandescent bulb - over its 25,000 rated- lifetime the Cree 9.5W (60W) bulb saves 1260 kWh of energy, $139 in electricity costs (based on 11¢/kWh), and 25 incandescent bulb replacements. Cree LED Bulb vs. CFL The Cree LED Bulbs are also attractive replacements for twisty CFL bulbs. The Cree bulbs use less energy, have a longer ratedlife, and contain no mercury. And unlike some CFL bulbs the Cree LED Bulbs are dimmable with most incandescent dimmers, have a pleasing color temperature and are instant-on. Cree Lighting Technology To achieve incandescent-like omnidirectional illumination approximately 20 Cree-manufactured LED Arrays are mounted on a cylinder and placed inside
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stores, restaurants, industrial, parking and street lighting. In fact, Cree was the leading supplier to the world’s largest LED street lighting upgrade completed by the City of Los Angeles in 2013. LED User Support Cree manufactures high-intensity LEDs having superior price/performance by combing highly efficient InGaN materials with proprietary G-SIC® substrates. Cree LEDs are available in chips, components, modules, and in lighting products for end-users. Cree offers complete applications support to lighting manufacturers, driver manufactures, solution providers, and other users of Cree LED components and modules. A few of the services include thermal simulation, photometric testing, binning, electrolytic capacitor evaluation, and dimmer compatibility. More Cree Technology In addition to lighting devices, Cree manufactures advanced SiC power MOSFETs and Schottky diodes to 1700 volts as well as SiC and GaN RF power amplifier devices to 11 GHz.
PRODUCT HIGHLIGHT
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Lighting Electronics
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TECH ARTICLE
Cutting Edge Flat Screen Technologies Rob Riemen EEWeb Contributing Author Do you still use a Cathode Ray Tube (CRT) monitor? The big tube TV’s and monitors, that dominated the display market from it’s inception in the 1950’s up until the beginning of the millennium, have rapidly lost their dominance. The new kid in the game, the flat screen, is smaller, healthier, and produces a much higher quality picture. Because of these characteristics, flat screens have taken over the display industry. Through the evolution of display technology, a slew of methods are being used to produce a quality picture. The main form of displays that are available for purchase are Plasma, (Organic) Light Emitting Diodes (O)LED, and Liquid Crystal Displays (LCD). Each provide a crisp, clear picture over the outdated CRT displays, but OLED displays are becoming the standard, and the future of flat panel technologies. Electronic displays have become a fixture in the home ever since CRT displays became cheap and readily available, but with advances in display technology, flat panel displays, such as plasma, LED, and LCD , have pushed the CRT down from it’s throne, leading to revelations in new screen technologies. What started as a few experiments with cathode rays by J.J. Thomson in
1897, turned into a whole new industry of displays. J.J. Thompson was able to deflect cathode rays, which is one of the main functions of the commercially produced CRT. Engineers of Western Electric started to produce commercial display products based on this design. But, the television in the form of a CRT, as we know it today, wasn’t produced commercially until 1934 by Telefunken. Over the next several years, display technology remained relatively stagnant, in terms of televisionesque displays. Other types of display technology were developed such as the Direct-View Bistable Storage Tube in 1968, which was able to provide a static display, one that didn’t need to be refreshed consistently. Around the same time LED displays began entering the main stream display market, but they were mainly used as business displays, rather than in consumer televisions. The technology to implement LED technology into commercial televisions didn’t materialize until much later. LCD technology began to evolve in the mid 1980’s as twisted and super-twisted nematic LCD screens began entering the market.
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Lighting Electronics
Each display technology has the same goal in mind, that is, produce a large number of high quality pixels in order to create a crisper, cleaner picture at high resolutions.
What started as a few experiments with cathode rays by J.J. Thomson in 1897, turned into a whole new industry of displays. J.J. Thompson was able to deflect cathode rays, which is one of the main functions of the commercially produced CRT. Engineers of Western Electric started to produce commercial display products based on this design. But, the television in the form of a CRT, as we know it today, wasn’t produced commercially until 1934 by Telefunken. Over the next several years, display technology remained relatively stagnant, in terms of televisionesque displays. Other types of display technology were developed such as the Direct-View Bistable Storage Tube in 1968, which was able to provide a static display, one that didn’t need to be refreshed consistently. Around the same time LED displays began entering the main
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stream display market, but they were mainly used as business displays, rather than in consumer televisions. The technology to implement LED technology into commercial televisions didn’t materialize until much later. LCD technology began to evolve in the mid 1980’s as twisted and supertwisted nematic LCD screens began entering the market. These LCD screens didn’t make much of a splash in commercial displays until the thin film transistor (TFT) LCD was introduced in 1986. The next step in display technology came in the form of plasma televisions. Plasma televisions were released in 1995 with a low resolution by Fujitsu. The most recent development in display technology is Organic LED technology. It is taking over the market and is able to produce a high quality picture without using a
TECH ARTICLE lot of resources. Oddly enough, none of these display technologies are directly related to each other. Besides LED’s and OLED’s all of the other types of flat screen technologies are separate in their own right. The big three screen technologies are all available today, each trying to claim their stake in the flat screen market. So what makes each display technology so different, and why do we need three different types of screen technologies? OLED, Plasma, and LCD, constitute of most of the flat panel displays used for televisions and monitors. Since each display technology is conceptually different, it is best to understand each technology in order to see why each type exists. Starting with the earliest developed flat screen technology, LCD displays have become a fixture in the display world. LCD takes advantage of the light modulating properties of liquid crystals. Simple LCD displays are those that are commonly used in calculators and other simple displays. But, those displays do not produce the colors needed for current display demands. In order to create large displays using LCD technology thin-film transistors (TFT) must be implemented. In order to make the transistors work with the liquid crystal, transparent conductive Indium tin oxide (ITO) layers must be engineered to contain small capacitors with a layer of insulating liquid crystal. When all these work together a single pixel can be displayed. Hundreds of thousands of these individual TFT-LCD setups must be interconnected across the display and once that occurs, higher resolutions can be achieved. Each display technology has the same goal in mind, that is, produce a large number of high quality pixels in order to create a crisper, cleaner picture at high resolutions. In comparison to the LCD technology, the LED televisions are built around thousands of mini LEDs. The type of LED’s that are able to be used to make flat panel displays is solely organic LED. The difference between normal LEDs and OLEDs is the fact that the layer in which emits light from the supplied electrical current is a film of organic compound.
Figure 1: Super-Twisted Nematic LCD Screen
Figure 2: Flexible OLED Screen
The semiconductor layer that is standard in all diodes is now organic and placed between two electrodes. Each pixel is
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Lighting Electronics
Figure 3: OLED Schematic
made up of three organic diodes of green, red, and blue. These are driven together to produce a full color display. This is done without a back-light as the LEDs produce their own light. The same can be said for plasma displays. Plasma displays represent pixels in the form of cells. Each cell contains electrically charged ionized gases which produces an effect similar to miniature fluorescent lamps. This means that plasma displays have the capability for a broad spectrum of colors as well as a bright picture. Although with all of the technologies available for flat screens, each one has their ups and downs based on the physics described above.
to pushing the limits of picture quality. With a contrast ratio of 1000000:1 and above and a better display of colors puts the OLED display at the forefront of display technology. Based on the technology advancements with OLED and the green technology behind these flat screens proves that they are the prime candidate to be the future of display technology.
Each screen has benefits that make it a better choice when purchasing, but which gives the most overall value? Taking into account brightness, contrast, color, resolution and sharpness and cost, we can compare the qualities of each flat screen technology and provide an insight to what the future of flat screen technology may be leading to.
Meharris. OLED EarlyProduct. Digital image. Wikipedia. Wikimedia Foundation, 10 May 2001. Web. 18 Sept. 2013. ■
LCD and plasma screens are perfect solutions for the average consumer. The plasma screen is always bright based on the fluorescent lamp physics with a competent contrast. LCD screens do not stack up in any way compared to the other technologies and in some cases need an LED backlit display in order to provide a significant brightness. But, they are much cheaper than the other options. OLED blows these two out of the water when it comes
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BIBLIOGRAPHY Medienstelle. BBC STN Matrixanzeige 540×270. Digital image. Wikipedia. Wikimedia Foundation, 28 July 2012. Web. 18 Sept. 2013.
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