APRIL 2010: Do you remember the HP-35 calculator that Hewlett-Packard (HP) launched way back in 1972? It was a hot favourite amongst engineers, being the only pocket calculator with transcendental functions at that time. It cost $395, and believe it or not, the price tag was so heavy because the device used light-emitting diodes (LEDs)! Today, LEDs are used even by school children for their science projects—say, an experiment to light up little bulbs using a spinning magnet. That is how common these tiny ‘digital’ lights have become.
At a time when their cost was prohibitive, LEDs were used merely as indicators in electronic devices. The fact that these bud-like lights consumed very little power, gave out very little heat and had a long life made them very popular and led manufacturers to explore various other applications. They are now used as backlights for digital displays, including liquid crystal display (LCD) flat televisions and computer monitors, sustainable lighting systems such as solar lanterns and solar street lights, as well as conventional home lighting. Even as these applications slowly gain momentum, newer ones such as automotive lighting and mobile projection are cropping up.
This quick uptake of LED technology can be attributed to the fact that the industry has been keeping pace with Haitz’s Law—a prediction by an erstwhile HP employee called Ronald Haitz that the amount of light that can be produced per diode (performance) would increase twenty-fold every decade, while the cost of that light would decrease ten-fold.
Paul Thieken, director of marketing-LED Components, Cree, stresses that over the past 40 months or so, the performance of high-power LEDs has improved drastically. “The most exciting improvements are the greatly increased light output (flux), improved efficacy (lumens-per-watt) and the colour quality and stability. These improvements are exciting because they have enabled commercially-viable LED lighting solutions which are now available to the consumer,” he adds.
Commenting on other associated developments, Marion Reichl, press officer, OSRAM Opto Semiconductors GmbH, says, “There are several improvements within the last few years that have given LED technology a real drive… ceramic packages for better thermal management; increase in efficiency within a short timeframe, with the help of chip technologies; organic LEDs (OLEDs) as a light source of the future; long-life, high-brightness white LEDs with longer maintenance intervals and better total cost of ownership; and so on. These improvements sup-port the fast and extensive adoption of LEDs for different applications.”
“LED is an initiative towards lowering energy demand and consumption, through lower power consumption and higher output,” says Hari Chereddi, managing director, Sujana Energy Limited. In this regard, he remarks, “The three most exciting improvements have been in the areas of applicability, availability and affordability of LEDs from the perspective of a common man. Applicability to our day-to-day lighting needs, availability in most shapes and sizes and, most significantly, becoming affordable to all, thereby providing limitless opportunities for ‘linking light and life’… Sujana Energy sees this as one of the most exciting areas of growth.”
According to Ajay Goel, CEO, Goldwyn Limited, the payback period of LED-based lighting solutions with respect to conventional technologies is as follows:
1. Streetlights for the governments/municipalities: Immediate as the cost of putting up power plant (for the amount of power saved) will be more than the cost of LED streetlights
2. Office LED lights: 18 months to 36 months
3. Other LED lights: 30 months, on an average
So far so good, and it promises to better, as there is a lot of LED-related research happening across the world. “However, major LED manufacturers have the most expertise and also the largest resources to put towards research,” comments Thieken.
You heard it right. An LED is part and parcel of the digital world. In fact, it is a simple, little ‘chip’. Even the manufacturing process bears a lot of semblance to that of computer chips. A p-n (positive-negative) junction is created out of a suitable semiconductor material. When electrons flow from the anode to the cathode, they move to a lower energy level, emitting a photon of light. The light could be red, green, blue or amber depending on the materials used to make the diode. The light from different coloured LEDs may be combined or a blue LED lens may be coated with phosphor to make white light.
LEDs are used as components in electrical and electronic devices, as well as for larger applications such as automotive or home lighting.
Not alone, though, the research work is done in partnership, points out Reichl. OSRAM Opto Semiconductors has a broad network of partners in the scientific community with connections at universities and research institutes. The company is also active in projects supported by the public sector (and there is quite a lot of thrust from this front, as LEDs are a good solution to today’s power-guzzling lighting equipment).
Evidently, there is a shove from all directions to take LED technology forth. Here is a sample of what is happening and what is in store.
LED in your living room
Efforts are on make LEDs the de facto standard for home and public lighting. Although LED lights are still too costly to motivate the common man to go for them, power savings, long life and low maintenance requirements have resulted in companies opting for LED-based lighting systems for their offices. Today, the most efficient LEDs are about ten times more energy-efficient than incandescent bulbs.
Also, with LEDs, it is possible to develop solidstate lighting (SSL) products, that is, lamps made using LEDs and OLEDs rather than electrical filaments, plasma or gas. The light weight and no brittle parts make such lamps robust and shock-resistant. The lifespan is also longer. They are now used mostly for traffic lights, remote controls, etc, but soon they might rule the home lighting market.
While it might be a few more years before we replace all the bulbs at home with LED lamps, the process of phasing out the traditional energy-guzzling incandescent bulbs has already begun in several countries, including parts of Australia, Europe and South America. The United States of America is targeting 2012, and is even holding contests such as the L-Prize, to spur lighting manufacturers to develop high-quality, high-efficiency solidstate lighting products. 60W bulbs account for 50 per cent of the domestic incandescent market, and replacing these with LED bulbs would save enough electricity per year to light 17.4 million households. It would also avoid 5.6 million metric tonnes of carbon emissions annually. The US Department of Energy hopes this to be the outcome of the L-Prize.
A list of the 50 best inventions of 2009 published in TIME magazine in November 2009 included Philips’ entry to the L-Prize (which also happens to be the first entry to the contest). Philips’ LED bulb emits the same amount of light as its incandescent equivalent but uses less than 10 watts and lasts 25 times longer.
According to the press release, the Philips submission will now undergo comprehensive evaluation, including performance testing conducted by independent laboratories, field assessments conducted with utilities and other partners, long-term lumen maintenance testing and stress testing under extreme conditions. Consumer pricing and retail availability are yet to be determined.
Reichl shares, “The OSRAM Parathom Classic is the very first bulb-shaped LED lamp, which constitutes a true substitute for a 40W incandescent lamp. This move will speed up the advance of LED technology as a genuine alternative for general lighting applications.” The company is also aiming to develop and market an LED for SSL applications that offer a continuous spectrum, exactly like natural daylight.
The price of LED lamps is still prohibitive when one considers using them for the lighting needs of an entire house. Leading brands might cost more than $20 a piece, while Chinese alternatives are cheaper. Prices will inevitably fall, because the writing on the wall is clear—LEDs are the future of home lighting. Despite the high initial costs, commercial organisations worldwide have already started adopting LED-based lighting because of the low TCO it offers in the long run, as well as to meet energy-related regulations.
India will also walk in step with the LED revolution happening worldwide. “We strongly believe that standardisation of LED lighting in India is a pre-requisite to prepare the market for the launch of superior products. To sustain this effort, Sujana Energy is working with bodies like the Bureau of Energy Efficiency (BEE) to help define LED luminaire specifications to meet global standards in India,” says Chereddi.
LEDs are a great option for street lighting, because these are economically and environmentally sustainable. By moving to LEDs, a town can save lots of power, avoid a lot of carbon emission and also reduce the total cost of ownership because LEDs have a long life and are practically maintenance-free.
The first example of this kind was the Italian village of Torraca, which spent 280,000 Euros to convert all its street lamps into LED lamps, reducing their energy and maintenance costs by 70 per cent. The City of Ann Arbor in the US followed suit and replaced a few thousand streetlights. The authorities noted an energy cost saving of around $10,000 and an additional $40,000 in maintenance costs last year from using LED lights instead of incandescent streetlights. The city therefore plans to replace more of its streetlights by next year.
LEDs are a great option for street lighting, because these are economically and environmentally sustainable. By moving to LEDs, a town can save lots of power, avoid a lot of carbon emission and also reduce the total cost of ownership
There are many more examples of public areas going for LEDs, parking lots in Boston and the famous Times Square Ball (a crystal time ball full of lights put up at the Times Square, Manhattan, NewYork City, every New Year’s Eve) being the well-known ones.
Engineers involved in designing innovative and affordable LED lighting solutions can now benefit from a broad product portfolio of LED drivers, alternating current (AC)/direct current (DC) and DC/DC power management devices, wireless and wired interface control and embedded processors. They have the option of not only controlling the power stage but regulating LED currents as well, eliminating the need for multiple components and reducing the system cost.
A very significant part of LED lighting is the driver design. “The reliability of the driver is a crucial factor to achieve longer life expectations. While designing the driver, it is important to pay attention to the selection of components, which can give a longer lifetime,” says Apoorva Awasthy, business development manager-analogue, Texas Instruments India, which also offers a suite of LED design tools.
LED lighting systems can be designed to accurately control voltage and current regulation for precise LED light intensity and colour mixing, temperature monitoring to prevent thermal runaway, intelligent and adaptive dimming of the LED, and fault detection (over voltage or current, blown string). Communication with external systems is also possible via power-line communication (PLC), wireless technology or interfaces.
Chereddi recollects, “A rather interesting application of LEDs in recent times has been in the areas of mood-based and architectural lighting. A great example of that is at NYC Waterfalls, where a series of manmade waterfalls installed around New York Harbour have been lit up using LED lighting fixtures to recreate the effect of moonlight on water. The application of LEDs in media, entertainment, outdoor displays, TV and cinema is at an early stage—this century will be lit up by LED, just as the incandescent bulb largely lit up the last.”
Driving home with LED
LEDs have been used for the amber and red taillights in cars for quite some time now, but as far as forward-lighting goes, it has been discussed for long but not implemented, as the efficiency of LEDs was insufficient for headlights thus far. Prototypes have been demonstrated since 2006, and hobbyists have tweaked their cars to fit special LED headlights. However, it’s only now that LED headlights are showing signs of becoming part and parcel of mainstream car models. Headlight maker Hella is working on at least 13 models of car headlights with LEDs.
“With the AUDI A8, it was demonstrated now for the first time how this advanced feature can be realised in a volume car. We expect this contribution of LED technology to leave the level of high-end vehicles and reach the middle-class segment in reasonable time,” hopes Reichl.
While car headlights are usually 12V applications, the US military seems to have even started using 24V LED headlights for their trucks.
LED key for mobile projection
Reichl points out, “An application that cannot be realised with other light sources (except lasers) is one of the more consumer-oriented applications—projection from mobile devices (phones or cameras) with embedded or companion projectors. High-performance LEDs are the key to this application, with high efficiency of the top emitting LED chips, the small size, long lifetime and high product quality.”
Other than miniaturising mobile projectors, LEDs have also helped in blowing up screens. Flatscreen displays with LED backlights are all the rage now. The image quality is much better when LCD TVs use LEDs as the light source instead of fluorescent lamps. LED TVs are more environment-friendly, as these consume less power and use no mercury in their manufacture. LEDs are also small and produce less heat, so these can be housed in thinner cases—the reason why you can now find really flat screens (only about 5cm thin) and even flexible displays.
“The advent of light-emitting diodes (LED) technology could be counted as one of the major innovations in the flat-screen display space. LED-based flat screens provide marvellous visual appeal, lower energy consumption, longer lifetime, improved robustness, etc,” says Naved Chaudhary, head-marketing, Intex Technologies (India).
While Samsung, Sony, LG, Vizio and Panasonic all have launched LED-based LCDs, Sony and Samsung have gone a step further and launched OLED-based displays. OLEDs will one day replace liquid crystal displays, as these are more eco friendly and offer a much higher display quality and power-efficiency. An OLED display comprises layers of an organic material (polymer) that can emit photons (and therefore light) when electrons are conducted through them.
Larger wafers, lower cost
“As LED performance continues to improve, more and more lighting applications are becoming viable for LED lighting. Recent developments include the cost-effective replacement of linear and compact fluorescent light fixtures with LED lighting products, as well as the use of LED lighting products for commercial retail and display lighting,” says Thieken. “However, the challenges facing LEDs and LED lighting continue to be related to the higher first cost of LEDs versus traditional lighting and the need to simplify the use of LEDs when designing lighting products. Cree and other LED firms are constantly working to lower the cost of LEDs through the use of larger wafers, increased manufacturing efficiencies and greater performance. In addition, new advancements such as Cree’s recent ‘EasyWhite’ LEDs simplify the design and manufacturing of LED lighting products by eliminating the need for complex LED ‘mixing’ recipes when building these products.”
Like Cree, several other LED manufacturers (most of them being in Taiwan, Japan and China) have started using 10cm and even 15cm wafer substrates instead of the traditional 5cm ones. The larger the substrate, the lower the cost of production. As the industry moves to larger wafer sizes, LED manufacturers can reduce the cost and expand their manufacturing capacity even further.
Kapil Sood, director, Amptek, which claims to be India’s first LED customising company, explains that the use of LEDs for large-scale lighting solutions offers significant advantages in terms of the total cost of ownership.
“Performance of LED light fixtures can be divided into the light/optical efficacy, the electrical performance, and the outdoor protection from dust, water, etc. LED light fixtures are more efficient as no light is wasted and can be directed onto the surface or object. As for the electrical performance, we offer LED light fixtures using specially-designed constant-current drivers having a power factor greater than 0.97, efficiency greater than 85 per cent and total harmonic distortion less than 10 per cent. For protection of LED light fixtures, we offer International Protection Rating IP65/IP67/IP68 rated fixtures depending upon the usage, i.e., outdoor wall washers, fountain lights, swimming pool lights, etc,” he says.
He notices a lot of demand for customised lighting solutions in the commercial and industrial areas, as there is a great opportunity to replace halogen, T8 tubelights and compact fluorescent lamps with LED fixtures. LED lights have a life of over 50,000 hours. So, besides energy saving, the user also saves a lot on the cost of replacing the lamps frequently.
Researchers and manufacturers are also figuring out other techniques to lower the production cost of LEDs, and hence the price of LED-based products. One such method was announced by Cambridge University last year. It claims to have found a way of making gallium nitride (GaN)—a semiconductor used to make LEDs. This will enable production of LEDs at one-tenth of cur-rent costs, by using 15cm silicon wafers instead of 5cm sapphire wafers.
Helping burn the midnight oil
Apart from lowering the cost of production, the industry faces the challenge of increasing the performance of LEDs, that is, the amount of light produced per unit of electricity consumed (measured in lumens per watt (lm/W)). Today’s white LED fixtures average around 46 lm/W, which is much higher than what incandescent bulbs and fluorescent bulbs have been able to manage till date. Fixtures with 100 lm/W or even 140 lm/W are easily available off-the-shelf.
The greater the performance, the more the power saved, and the stronger the reason to buy LED-based products. No wonder, companies are constantly trying to increase the efficiency of their products.
Just recently in February, Cree Inc. demonstrated a white LED with an efficacy of 208 lm/W. According to the press release, “Cree’s tests confirmed that the LED produced 208 lumens of light output and achieved 208 lumens per watt efficacy at a correlated colour temperature of 4579K. The tests were conducted under standard LED test conditions at a drive current of 350 mA at room temperature.” It might be a while before a 208lm/W product hits the market, but the company already offers lighting-class LEDs that can deliver upwards of 120 lumens per watt. “We have also recently introduced a multi-chip LED component optimised for use in LED directional bulbs that supplies 1500 lumens of light output,” notes Thieken.
He adds, “High-power LEDs will continue to offer increased levels of performance. We believe other developments will enable lighting customers to simplify their designs and manufacturing and also reduce the cost of LED lighting products.”
Organic might be the answer
It is evident that almost every company is focusing on two things as far as research goes: increasing the performance and decreasing the cost.
If manufacturers are able to figure out the right technique, organic LEDs made using inexpensive polymers might be the answer. However, at present, OLEDs are known to have a lower efficiency and lifespan than inorganic crystalline LEDs. Despite that, GE seems to have found out how to produce nice, bright OLEDs.
Way back in 2004, the company demonstrated an OLED device that was fully functional as a 61x61cm2 panel, and produced 1200 lumens of light with efficiency on par with today’s incandescent bulb technology. Since then, GE has more than doubled the level of OLED efficiency using device architectures that are scalable to a large area and can be produced cost-effectively. The efforts to increase the efficiency and performance of OLED lighting have coincided with the development of a low-cost, roll-to-roll process for manufacturing these devices.
In 2008, they demonstrated the first roll-to-roll manufactured OLED lighting devices. This can be considered a key step toward making OLEDs and other high-performance organic electronics products at a very low cost. What is more, this effort was led by an Indian, Anil Duggal. By next year, we might see OLED lighting products from GE.
Quantum leaps ahead
Michael Bowers of Vanderbilt University, Nashville, USA, has developed an experimental technique that involves coating a blue LED with quantum dots that glow white in response to the blue light from the LED. The mellow yellow light produced by this method is quite similar to that of our incandescent bulb.
According to the Wikipedia, quantum dots are semiconductor nanocrystals that possess unique optical properties. Their emission colour can be tuned from the visible throughout the infrared spectrum. This allows quantum-dot LEDs to create almost any colour on the CIE diagram, providing more colour options and better-colour-rendering white LEDs. Quantum-dot LEDs are available in the same package types as traditional phosphor-based LEDs. Apparently, the Nanoco Group and a Japanese company have also tied up to design, develop and produce these quantum dots.
In all, it is quite a promising scene. There is a demand and a supply for LEDs, for niche as well as mass purposes. Manufacturers are hooked onto so many R&D programmes, to reduce cost, increase performance, improve the colour rendering and uniformity of light, achieve constant brightness through-out the life of the product, enhance the packaging, customise the LED components to suit specific applications, etc in order to cater to niche industries as well as mass adoption.
“At this point of time, LEDs are thriving to lower energy demand but in the future LED luminaires with superior aesthetics, automatic controls, thermal management and lower costs will lead the way. These will further promote wider applicability, mass availability and greater affordability,” says Chereddi. “We believe that the magic differentiator will be a consortium approach of system integrators, LED manufacturers and electronics manufacturers, which will then lead to market consolidation and leadership. This will create better reference designs, superior products and lower total costs of ownership,” he adds.
The author is a freelance writer based in Bengaluru. She writes on a variety of topics, her favourites being technology, cuisine, and life