Future Looks Bright for LED Lighting

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New technologies in design, manufacture, test and software-based control are improving the chances of LED winning in the lighting market. Innovations dot the scene, as companies strive to make a sub-$10, 60W incandescent-bulb equivalent

Light effects by OLED lighting (Image courtesy: www.osram-os.com)

Janani Gopalakrishnan Vikram

Friday, September 14, 2012: At the LED Show 2012 held in Las Vegas a month ago, a keynote speaker noted that there was hardly any light-emitting diode (LED) lights used in the conference venue. The reason: high costs.

Well, that brings us to the crux of the matter right away. LED lighting offers benefits galore: low power consumption, long life, good colour quality, configurability and so on. The efficiency is also on a constant rise. However, the single factor that puts it out of reach of the masses today is the initial cost.

Globally, the LED penetration for general lighting is still low at approximately 7 per cent in 2012. According to some recent reports, the LED segment currently accounts for less than 3 per cent of India’s Rs 70-billion organised lighting market, although it is growing at a healthy rate.

“LEDs are perceived to be expensive as their initial cost is much higher than the traditional lamps, but in the long run LEDs prove to be much more economical considering the energy savings, long life and the reduction in maintenance and replacement costs. That said, the industry is investing heavily in R&D to offer LED-based lighting solutions at a more affordable price for the consumers,” says Indranil Goswami, head-Lighting Application Services, Philips Lighting India.

The dream of every player in the LED lighting industry today is to create a commercially-feasible LED lamp that is equivalent to a 60W incandescent bulb, saleable at a cost of $5 to $10. The race to achieve this is dotted with innovations all along the way.

General well-being

Overall, there is a positive feel in the LED industry, because all common parameters are improving. The diode technology has improved significantly, resulting in high-power light-emitting diodes with a higher lumen output that are capable of replacing other lamps. This has resulted in a wider application of LEDs.

The last few years have also seen a remarkable improvement in the efficacy of LED chips, packages and lamps, measured in terms of lumens emitted per watt (Lm/W) of electrical power consumed. The amount of light that can be extracted from one LED, commonly known as the lumen pack, is also rapidly approaching levels that make sense in practical lighting applications.

Reverting to a common scale, Goswami points out that the efficiency and light output of LEDs are increasing exponentially, effectively doubling every 36 months, in line with Moore’s Law. (According to Moore’s Law, the number of transistors on a chip roughly doubles every two years.)

Dr Michael Fiebig, director, marketing and business development–solidstate lighting, Osram Opto

Semiconductors, explains that LED efficiency, colour quality and life have all improved in the year gone by. LED efficiency has been improved significantly, in both warm white and cold white colour temperatures. LED technology now provides the basis for a broad spectrum of application-specific solutions for colour temperatures from 2700K to 6500K and various colour rendering index (CRI) values from 70 to 95. High CRI values, in particular, are now providing R9 and R13 values in the range of 90, which helps to achieve an impressive colour impression.

The lifetime has also improved significantly to more than 100,000 hours for white LEDs, bringing down maintenance and replacement costs significantly. Plus, quality standards have now been set for actual environmental conditions, especially in terms of humidity, temperature cycling and gases. There is also a lot of standardisation going on to improve the quality and reliability of LEDs.

“LED technology is more than competing against conventional technologies. This progress has been achieved by overall improvements in the technology, not only in chip development but also in phosphor and package technologies,” says Dr Fiebig. “System yields have reached about 80 per cent including thermal, electrical and optical components. Major contributions are being made by optimised LED drivers, light management systems and sensors (ambient light sensors and motion sensors).”

Overall, the industry is very enthusiastic and teeming with innovations. Take a look at some of these.

Omni-directional LED lamps

“A bulb is a bulb. The conventional LED does not dramatically change the customer’s image of incandescent bulbs. Omni-light pattern bulbs might fulfil the customer’s basic requirement of a bulb. Perhaps these don’t look like a traditional bulb, but users can install them in their fixture and the light pattern is similar to incandescent,” says Edward Huang, head-Lighting Business Unit, Everlight Electronics.

Like Everlight, other companies are also working on omni-directional lamps to widen the illumination pattern of LEDs.

The limited illumination pattern of LEDs has been a lingering problem. Although the viewing angle has been increased from 30 degrees in the past to 120 degrees now, the intensity is only about 50 per cent at the ends of the pattern, thereby killing the benefit of the wide viewing angle. Like the incandescent lamp, the LED must provide an illumination pattern on all sides, if it is to become a norm in general lighting. Many methods have cropped up to overcome this issue.

Diffusion using a frosted, diffraction-style lens or canopy is one method. Although partially successful, this may reduce the total light output and not provide an even light pattern on all sides.

Another way is to mount many LEDs pointing in all directions, but this is costly and difficult to manufacture.

The omni-directional LED technology appears to be a simpler solution. This patented technology incorporates a continuously convex reflector positioned in line with the light pattern of one or more LEDs to provide a wide illumination pattern. It is a simple technique based on the reflective law of incidence and reflection.

Going organic

An upcoming generation of organic LEDs (OLEDs) promises to be thin, efficient and environment-friendly. In OLEDs, the emissive electroluminescent layer is a film of organic compound, which emits light in response to an electric current. Apart from being very useful and efficient in creating flexible and pleasing displays for electronic products, OLEDs are also going to make a mark in low-energy lighting.

“Major researches are happening in OLED technology, and this could change the face of LED lighting in the future. OLEDs emit a soft and diffused light offering a new type of design freedom that is also energy-efficient. OLED lighting applications are thus particularly attractive to high-end retail, hospitality and residential construction markets for decorative and ambience creation purposes. These also hold appeal for the design-conscious consumer,” says Goswami.

Phillips, GE, OSRAM, and almost all other LED lighting majors are into OLED research and development.

Quite recently, Philips launched its Lumiblade GL350 OLED lighting panel. The pack consists of three 3.3mm thick, small squares, each edge measuring less than 13 cm. The tiny wonders are capable of 120 lumens each, which is considered to be a very good output for OLEDs. The panels could be suitable for general lighting purposes as well. These are supposedly cooler than other OLED counterparts and previous Lumiblade products.

It is not just the lighting industry that is betting big on OLEDs. In March this year, Audi demonstrated its new glowing OLED lighting at the Audi Electronics Centre in Ingolstadt. Stephan Berlitz, head of Lighting Technology and Electronics at Audi, commented that the desired homogeneous visual effect would not be possible with today’s LEDs.

“These are individual points of light that need additional optical devices—reflectors, optical conductors or scatter optics. OLED surfaces are themselves the source of light, and the thin plates also look attractive. They weigh little, light up extremely fast, develop only a small amount of heat, last several tens of thousand hours and don’t consume any more energy than conventional light-emitting diodes. OLEDs suit Audi perfectly because they combine high-end technology, maximum precision and super design,” he said.

Audi still needs to overcome the lights’ 80°C temperature limit before the technology enters mainstream models.

Smart designing

There is a lot of thrust on smart designing in the LED industry. Experts feel that to bring down the cost of LEDs, the industry needs an integrated solution that includes more efficient design and easier manufacturing, apart from trade tricks.

There are varied design goals. One, of course, is to improve the colour control, brightness and efficacy of LEDs. There is no dearth of innovation on this front but it’s more important to simplify the things—both from a manufacturing perspective as well as market perspective. From a manufacturing perspective, the purpose is clear—simple designs are easier and cheaper to manufacture. From a market perspective, the goal is to make the selection process simpler for the customer.

Today, the LED market is a bit confused, at least at the consumer’s end. Selecting an incandescent bulb is easy—you just pick what wattage you need. But, there is no uniform parameter by which LEDs are evaluated or marketed. The consumer is confused with keywords and figures.

So one of the industry’s new design goals is to provide an alternative to the traditional ‘bulb’ that would have a similar form factor and lumen output. The more educated customers can filter their choice further based on the finer details.

At the recently held LED Show, Cree promoted a system-level approach to designing solidstate lighting systems. From testing and troubleshooting to improvements and cost reductions, the company noted that everything has to be handled design-up.

Remote phosphor technology

Remote phosphor technology is another key innovation area in the solidstate lighting space. It is touted to be a solution to the cost-reduction dilemma. Traditionally, LED manufacturers have adopted either of two methods to produce broad-spectrum white light. One method involves mixing different coloured LEDs, while the other involves depositing a yellow phosphor layer on a royal-blue LED die to convert the wavelength of the light. Both processes are very inefficient. The first method is very costly, while the other is inconsistent (since the phosphor coating degrades at high temperatures).

Remote phosphor technology overcomes this problem by bonding the phosphor coating to a substrate that is at a distance from the LED die. Since the phosphor is away from the LED die, it reduces the temperature of the phosphor coating and increases the longevity and reliability of LEDs. It has been found that remote phosphor technology offers manufacturing efficiencies as well.

Intermatix recently launched its new ChromaLit XT, which integrates remote phosphor technology to produce a material that can withstand temperatures of up to 270°C and increase LED system efficiency by up to 30 per cent.

Companies like Cree and Philips also have a strong remote phosphor technology portfolio. Interestingly, the large potential market for remote phosphor technology based lighting systems is causing industry majors to indulge in a patent-filing spree. There is a veritable race ensuing between Cree and Intermatix.

Alternating-current LEDs

Alternating-current (AC) LED assemblies can produce light output levels and efficacies of DC-LED assemblies, while eliminating the AC-to-DC converter and other electronic components that DC-LEDs require. The AC-LED approach allows operation directly from line voltage or low-voltage AC transformers.

AC-LEDs can work without the use of drivers, which are needed by DC-LEDs to convert the AC power into low-voltage regulated DC power. The working of AC-LEDs is simple. For each half-cycle of the AC’s sinusoidal waveform, half of the LEDs emit light and half are dark; this is reversed during the next half cycle. Like this, a large number of LEDs can operate in series, directly from line voltage.

However, an article by Laura Peters in LEDs Magazine points out that this approach often produces LED ‘strings’ with limited efficacy. Therefore several years ago AC-LED suppliers such as Seoul Semiconductor and Epistar began producing LEDs that operate directly from low to high AC voltages with simple control circuitry. This includes low-voltage direct AC to high-voltage rectified LEDs. The LEDs typically accept 12V on the low side up to 240V today.

AC-LEDs offer many benefits—from simplicity to scalability and better control. However, today these are used mainly for niche applications such as cove lighting, garden lighting and decorative lighting. It is expected that a few years down the line they might dominate the retrofit market.

The driverless design of AC-LEDs could bring down the cost of LED lamps significantly. Some companies are going for chip-on-board or surface-mount design implementations to bring down the cost further.

However, components cost of LED lamps and luminaires is still an issue, as also is improving the power management aspects of AC-LEDs. Once these are overcome, AC-LEDs could be the solution to the industry’s sub-$10, 60W lamp challenge!

Silicon-based manufacturing

“LED technology is still in a process of rapid development; the industry is on a growth curve in terms of brightness, efficacies and colour control. At the same time, there is still room for further advancements in terms of productivity, thereby reducing cost per lumen. The introduction of 15cm wafers into production is one major method adopted by Osram Opto Semiconductors to match market expectations,” says Dr Fiebig.

Osram researchers have also succeeded in manufacturing high-performance prototypes of blue and white LEDs in which the light-emitting gallium-nitride layers are grown on silicon wafers with a diameter of 150 mm. The silicon replaces the sapphire commonly used until now without any loss in quality. Already in the pilot stage, the new LED chips are to be tested under practical conditions, meaning that the first LEDs on silicon from Osram could hit the market in just two years.

“For LEDs to become widely established in lighting, the components must get significantly cheaper while maintaining the same level of quality and performance. We are developing new methods along the entire technology chain for this purpose, from chip technology to production processes and housing technology,” informs Dr Fiebig.

Other companies like Cree and Bridgelux are also touting silicon-based manufacturing as the ultimate path to lower the cost since silicon costs much less and is widely available. Toshiba has announced plans to manufacture such LEDs this year using Bridgelux technology.

Huang points out that there are other gradual improvements as well in LED manufacturing. For example, the industry is moving towards modular design. Plus, there is a lot of automation in assembly, especially in processes like gluing and socket mounting.

Digitalisation of light

Purpose-designed semiconductors with robust operating systems and programmable power electronics, programmable digital systems and software controls are revolutionising lighting. By digital control we mean not just the ability to customise the various aspects of the lighting system on-the-go but also the ability of the electronic components to communicate with each other and with the external environment.

Advanced lighting systems feature user-friendly and intuitive interfaces that allow you to change several settings—right from the shade and the colour temperature to the brightness. The lighting system can also alter its behaviour according to the constant changes in the natural environment.

This emerging ability to control lights, individually and collectively, is leading to the ‘personalisation of light.’ We can change the hues of our environment according to our moods or the needs of various events.

“Digitalisation of light is an important aspect for LED illumination. With this technology, we have the possibility of creating our own individual atmosphere. Easy light management for dimming and changing light colours is crucial,” says Dr Fiebig.

“Conventional incandescent to LED is what analogue is to digital. We can change only a few factors in conventional light, such as brightness and colour. In LED lighting, we can manage the light (even colour temperature) in a digital way. For example, when you come home, the light will turn on as the sensor catches your personal portable device (smartphone). Then according to your setup, it will auto-program your preference in scheduling timeframe with individual recipe and combination—for example, turn on the living room’s panel light and change to the lower CCT in the evening, or when you wake up in the morning. There will be so many new ways to use LED lights that are never possible with conventional light sources,” exclaims Huang.

In general, such dynamic and personalised lighting influences human performance metrics by synchronising our biological clock and providing cues that stimulate our brains. This can be used to improve factors like physical and mental wellness, and even employees’ productivity.

The Maastricht University Medical Centre and Philips Lighting have demonstrated that medical patients rest better in a lighting environment that mimics the natural day-night outdoor cycle. One of the focus points of this year’s LED Show was how lighting can be used to improve the general well-being of people. A recent report by the US Department of Energy (DOE) noted that with better lighting, employers can reap financial benefits from higher employee productivity. The Rensselaer Polytechnic Institute’s lighting lab expects optimal lighting schemes to improve learning in students.

Goswami notes that such intelligent and smart lighting solutions can also lead to a lot of power-saving, apart from providing luxurious and healthy lighting to consumers.

The industry majors do have a few futuristic solutions up their sleeves, but these are still not fully integrated or personalised. Also, there is no accepted standard operating system. So it might be a few years before we see such personalisation becoming common.

State-of-the-art testers

Improvements in test and measurement (T&M) are one of the key factors contributing to the advancement of LED technology in recent times. Several T&M equipment are being launched for the solidstate industry—for design to system evaluation and LM-80 (an important LED standard) testing.

For example, Orb Optronix recently announced the LM-80 active control lifetime test chamber for desktop testing of LEDs.

Gigahertz-Optik unveiled a single-pulse LED measurement system that can be used for binning of components for light output and colour. The BTS256-LED tester and companion LPS-20-1500 power supply rely on a photodiode for accurate characterisation of packaged or unpacked emitters. The device also includes a spectrometer for colour measurement.

Instrument Systems recently announced the LGS 250—a new gonio-photometer designed specifically for solidstate lighting applications. It can analyse angle-dependent special radiation, and is suited for use with small- to medium-sized LED retrofit lamps, luminaires and modules.

Labsphere Illumia has launched a spherical tester to measure thermal, optical and electrical properties of LEDs.

Cree has also been working on creating the TEMPO (thermal electrical mechanical photometric optical) testing program that it now offers to other luminaires as well. Supposedly, Cree’s TEMPO has many advanced techniques. For example, it performs thermal imaging on the electrolytic capacitor in the driver of a solidstate lighting product under test, since that capacitor is known as a primary source of failure in solidstate lighting products. It then provides the luminaire designer with a projection of the lifetime of that capacitor based on its specifications and the condition under which it is being operated.

Interesting products

The ongoing R&D in the LED industry is manifesting as interesting products in the market.

Osram’s Duris P5 LED, which withstands adverse conditions, is one interesting innovation. The product offers high luminous efficacy even at high currents and temperatures. This highly-efficient LED is also the first of its kind on the market for medium-power classes with particular resistance to adverse environmental conditions.

“Long-term tests with corrosive gases such as sulphur and chlorine cause no damage to the LED, and no significant decrease in luminous flux. Nor do long-term tests under sauna-like conditions, with high temperatures and high humidity levels, have any adverse effect on the LED,” points out Dr Fiebig.

Earlier, all LED lights had to be binned to maintain white light consistency and uniformity. The development of Philips’ Luxeon emitters offers freedom from binning as these are consistent and uniform.

Philips has also developed the smallest power LED with highest lumen density. “This LED is enabling the development of products in special lighting segments using a modular approach,” says Goswami.

The company has also developed an advanced power management system, which maximises operational efficiency while lowering the cost of installation, operation and maintenance. This power management system integrates the power supply directly into a fixture’s circuitry.

Philips’ Greenline Smart is a home-grown technology, developed to address the need for replacing the higher-capacity streetlights in urban areas in India. It features ingress protection (IP65), which means it is water- and dust-resistant for life. The luminaire can handle high voltage fluctuations ranging between 100V and 300V.

Recently, Cree engineers designed and constructed a retrofit lamp that achieves 170lm/W efficacy, using LEDs based on its third-generation silicon-carbide manufacturing platform called SC3. Through advancements in LED chip architecture, phosphor and a new package design, SC3 technology delivers what the company claims to be the most advanced LED components in the industry. The company’s new XT-E and XM-L high-voltage LEDs showcase the technology beautifully.

Everlight also has a line-up of products that integrate recent developments in thermal, optical and driver technology. The products feature lm/W improvements, as well as high voltage with linear IC combination for cost reduction.

In short, there is a lot of innovation happening, and a constant push to improve key parameters such as efficiency, colour rendering and lumen maintenance while bringing down the costs. Hopefully, all these efforts should culminate in an equivalent to the ubiquitous 60W bulb!

The author is a technically-qualified freelance writer, editor and hands-on mom based in Chennai

Some quick pointers for LED designers

Evolving technology means costs and bill of materials (BOMs) can go up just as rapidly. This means a lighting designer with a project idea might find that he can achieve a lot more than what he initially had in mind, potentially saving in costs, energy and installation time if and only if he understands the full potential of the technology he is working with.

The LED lighting industry is dealing with the challenges of pricing, branding, the retail channel and regulations. Manufacturers are turning to chip-on-board design and quality enhancements to overcome the price challenges and demonstrate the value.

LED lighting is really taking off in solar and off-grid applications, where LED lighting can provide much more than halogen, or where batteries are just not practical. Furthermore, solar street lamps are an interesting application, which involves a wider range of technologies than just solidstate lighting. Some of the key design issues that must be addressed are generating the maximum power out of the solar panel, charging up the battery for energy storage and getting the most out of the LEDs in an outdoor environment.

Today, the solidstate lighting market is focussed on system efficacy, which represents a more complicated challenge for electronics design engineers. Lighting electronics design engineers will need to place more emphasis on safety, power regulation, dimming control and communication protocol, sensing and wireless integration into the lighting fixtures.

—Ravi Pagar, regional director–India and Asean, Element14

Electronics Bazaar, South Asia’s No.1 Electronics B2B magazine

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