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2007: when Solid-State became the future of Lighting

issue 40 Dec / Jan 2007/8

This year the Solid-State Lighting market has seen significant growth due to the relentless research and production efforts of leading LED manufacturers which have created record breaking lumens per watt efficacy whilst offering high quality of light.

In 2007 the best LEDs became significantly more efficient than CFL’s and offered a better environmental choice. dr geoff archenhold reports on a vintage year.

Looking back on 2007, it has been an absolutely phenomenal year by any account for the lighting industry. Month after month I have witnessed LED and OLED efficiency records being smashed both for research and production LEDs, many of the traditional lighting companies started to set their sites on acquisition targets within the LED field and governments decided to act on climate change issues through new legislation and encouraging support mechanisms.
Traditional lighting industry positioning themselves for the LED future
For many years now, traditional lighting companies of all sizes have stated that LEDs were another lighting fad, similar to fibre optic lighting of the 1980’s and many were very keen to point out all of the bad points of a new technology. Indeed, when I presented LED trends and roadmaps to boards of traditional lighting companies many still believed LEDs were not practical for white lighting applications and were only suitable for RGB colour systems. Much of my time this year has been spent persuading the traditional lighting industry that LEDs are becoming mainstream lighting sources and helping them to understand how they should embrace a 5-year strategy to encompass LEDs as well as traditional lighting fixtures or face the real possibility of extinction.
My task became easier as the year progressed due to the acquisition fever that gripped the lighting industry with many LED companies being acquired by traditional lighting manufacturers. It all started in January 2007 with the acquisition of My-tronic, an LED fixture business, by Zumtobel group, followed by the acquisition of TIR Systems for US$64 million by Philips Lighting in March. Although Philips had originally laid out its aspirations during 2006 with the acquisition of the LED specialist Lumileds it wasn’t until the takeover of Color Kinetics for a stunning US$791 million in June that the lighting industry realised that Philips had become the first vertically integrated SSL lighting company.
Suddenly, the traditional lighting industry woke up and the second half of 2007 witnessed Cooper Lighting acquire IO Lighting and began investment in LED based lighting. Sumitomo Chemical of Japan also acquired OLED specialist CDT of the UK in September for US$286 million and there have been endless rumours that Cree would be acquired for its leading LED chip technology.
I predict further acquisitions of LED and control system specialists during 2008, especially those that have robust IPR and a growing presence in the market – watch this space.

The rapid increase in LED efficacy during 2007
During 2007 the LED industry witnessed an unprecedented level of innovation and virtually every month saw a new advancement in LED technology. Since 2006 the SSL industry has seen announcements covering the increase of white LED efficiency, records for single LED lumen outputs and a variety of new LED multi-die packages offering fixture manufacturers greater flexibility for designing lighting products.
For example, in January 2007, Philips Lumileds announced it had produced a white LED research device delivering 136 lumens at 350mA (115 lm/W) and 502 lumens at 2 Amps forward current (61 lm/W). This was the first time a major LED manufacturer had managed to operate a power LED at such a maximum forward current with reasonable efficacy and at a correlated colour temperature (CCT) of 4685K. To put this achievement in context, the light output performance was 17 times greater at the same electrical power than was available in 1999. It is predicted that by the end of next year the technology used within this research device will be transferred into production and the industry could witness the first single chip LED break the 500 lumen barrier!
In September 2007, the R&D labs of LED manufacturer Cree also demonstrated a single-chip white LED with an efficacy of 129 lumens per watt for a cool-white LED (5813 K) and 99 lumens per watt for a warm-white LED (2950 K). The results were verified by the National Institute of Standards and Technology (NIST) and the LEDs were tested at 350 mA and after five minutes of operation to ensure thermal stabilization.
Figure 1 demonstrates the increase in white LED efficacy from Cree and their expected roadmap until 2012.
In discussion with Mark McClear, Cree’s director of business development for solid-state lighting, he stated: “We [Cree] see no fundamental technical barriers to achieving the 150 lumens per watt (1W cool white Power LED @ 350mA) target by 2012, as called out by the U.S. Department of Energy roadmap for Solid State Lighting components.“
Dr. Klaus Ziemssen, LED Systems, Vice President and General Manager agrees and states that “We [OSRAM] think that the LED technology can substitute classical light sources in the midterm in applications where the main focus is on decorative lighting and longevity.”
The rapid increase in LED efficacy is not only limited to white LED technology and 2007 has seen some significant increases in both Red, Green and Blue efficacy as shown by Figure 2. In June 2007, OSRAM reported record results in the laboratory for green-emitting ThinGaN and red-emitting AlGaInP chips. The company expects the first LEDs based on these chips to go into series production by the middle of 2008. The Green-emitting (527 nm wavelength) LEDs measuring 1 mm2 achieved a luminous flux in excess of 180 lumens at 1 A. When driven at 350 mA, the chip produced 100 lm and consumed 1.4 W (equivalent to 72 lm/W). A red-emitting AlGaInP chip with a wavelength of 615 nm achieved more than 400 lm from an operating current of 3A. The new green XR-E LED from Cree announced in November produces a maximum luminous flux of 87.5 lumens at 350 mA and represents a 70% increase in performance over its previous version.

LED Efficacy in production today

Okay I hear you say, who cares about R&D efficacy values. What I need is efficient LED technology available in volume production today. Well, my reliable sources state that for high power devices you are able to obtain the following white LEDs in production:
Cree: cool-white (6500K CCT) is available up to 114 lm & 96 lm/W @ 350 mA. warm-white (3000K CCT) is available up to 80.6 lm & 70 lm/W @ 350 mA.
OSRAM: Golden DRAGON 70 lm/W @350mA or OSTAR 70-75lm/W @350mA (both at 6500K)
Philips Lumileds: Rebel cool-white (6500K CCT) is available up to 100 lm/W @ 350 mA.

Comparison with traditional light sources
Although rather difficult to compare to traditional light sources, one method would be to look at the typical efficacy and within the last 12 months individual white LEDs have increased significantly in efficacy as shown by table 1. The best production white LEDs are in excess of 105 lumens per watt. However due to their directional beam output the total useable optical light output performance is excellent as less collimation is required in the optical systems.
Interestingly, in 2007 LEDs have already become more efficient than Compact Fluorescent Lights (CFLs) at the light source but are substantially (~ x3) more efficient when used within a lighting fixture. Therefore during 2008, the LED industry has to ensure that the general public are made aware that LEDs are much more energy efficient, less harmful to the environment (each CFL contains ~5mg of mercury) and provides a better quality of light than CFLs.
I predict that the end of compact fluorescents will be much sooner than the conventional lighting companies may think (within the next 5 years) due to several reasons:

  • Consumer do not like the light generated by CFL’s.
  • Currently, consumers have to choose CFL’s as there is no significant choice of energy efficient light sources.
  • CFL’s take a significant time to get to a standard operating condition.
  • LED based system are already more efficient than CFL’s making them more environmentally friendly in terms of electricity consumed to light on task metrics.
  • Although LED systems are significantly more expensive than their CFL counterparts I believe consumers would pay more for quality and functionality of light.

Figure 3 demonstrates how the White LED efficacy roadmaps from the major LED manufacturers will enable White LEDs to displace CFLs by 2012 even if the costs of the LEDs are 20x more expensive. A typical 13W CFL generates approximately 800 lumens, the equivalent of a 60W incandescent bulb. However, by 2009 a white LED will have an efficacy of 135 lumens per Watt and require only 5.9W of electrical energy to generate the 800 lumens or twice as efficient as a CFL!
Now, I can remember buying a CFL from Philips nearly 15 years ago for about £14 and today they can be purchased for as little at 50 pence (a near 30x decrease in value) so I expect a similar trend to occur for LED based lighting although one could argue that the timescales should be shorter as LEDs are based on semiconductor technology and there are much less materials required in an LED fixture.
Importantly, take note, at these levels of efficacy the thermal management issues that have plagued LED design over the last few years will virtually disappear as there is only 5W of power to be dissipated.

Scalability of LED light sources to deliver useful light output
The last few years has seen the rapid increase in White LED efficacy for 1W devices driven at 350mA. However for the practical replacement of Halogen, CFL and fluorescent tubes LEDs have to deliver the efficacy at continuously higher forward currents.
As discussed previously, Philips Lumileds led the way with the launch in February of an R&D LED. However, in September 2007 the R&D labs of LED manufacturer Cree demonstrated a single-chip white LED with an output of 1,050 lumens driven at 4 amps in cool white, with an efficacy of 72 lumens per watt. The input power was 14.6W and the forward voltage was 3.65V. A warm-white version of the LED produced 760 lumens with efficacy of 52 lumens per watt. For the first time a single white LED chip had breached the 1000 lumen barrier and this was achieved without using any special packaging technologies.
Figure 4 illustrates what a significant leap in performance such a device would be compared to the current high powered white LEDs available on the market today. As the performance of LEDs at various forward currents becomes difficult to compare, figure 4 shows how modern high powered LEDs are becoming scalable enabling the fixture designer to choose any desired forward current to deliver the required fixture light output.
Although there is a difference in performance between cool white and warm white LEDs (known as the CCT gap) the difference is expected to reduce over the next few years with improved phosphors and better thermal LED packaging. Figure 5 shows the same LEDs but this time configured to plot the efficacy against the forward current to reveal how the LEDs become less efficient as they are driven at higher forward currents.
The ability to produce scalable light at higher forward currents has been achieved by using new manufacturing processes which overcome inherent limitations with previous LED chips that made them more inefficient when operating at high forward currents.
In February, Philips Lumileds managed to overcome such issues by ensuring their latest generation of LEDs operated effectively at high currents as shown by figure 6. However, by November 2007 Philip Lumileds launched the latest LUXEON® K2 with Thin Film Flip Chip (TFFC) technology making the first 1A rated LED with a minimum of 200 lumens available to the lighting industry. At its rated drive current, the LUXEON® K2 with TFFC operates at only 66% of its maximum power rating and delivers unprecedented performance for a single 1mm2 chip. The new K2 device has improved packaging which reduces the thermal resistance to only 5.5° C/W and allows the LED to be driven at higher currents (max is 1.5A) whilst lowering the thermal management engineering efforts and cost.
Referring to Figure 4 the K2 TFFC device offers the same performance as the R&D device announced in February at 1A and thus provides us with a high degree of confidence the production team at Lumileds will be able to deliver a 500+ lumen single LED by the end of 2008.
Not to be outdone, OSRAM Opto have in November announced it’s own high current LED called the Diamond Dragon, Figure 7. The LED combines impressive brightness of 250 lm at 1.4 A (max 2A) with a very low specific thermal resistance of 2.5 K/W, all in a SMT package. The high-brightness single-chip LED is based on a 2 mm2 chip manufactured in Thin-GaN technology with chip level coating. The typical power rating for the Diamond Dragon is in the 5 to 8 W range and the LEDs will cover the entire white range and will also be available in all other colours.
Increased usability of LED light sources during 2007
In 2006 nearly all of the major LED emitter available on the market had to be manually placed on a Metal Core PCB for manual or hot-bar soldering making the volume manufacture of LED fixtures difficult and expensive. However, 2007 has seen several impressive LED emitter packaging developments come to market significantly reducing the cost and ease of manufacture through the use of surface mount technologies suitable for automated pick and place production systems.
In addition new products launched included improved Moisture Sensitivity levels enabling products to be stored for longer and Lead free reflow solder compatible with automated soldering techniques.

Improving the LED performance to cost ratio
During the year the trend of most LED manufacturers has been to increase the performance of LEDs whilst trying to maintain LED margins thus improving the LED performance to cost ratio.
In March 2007, Philips Lumileds launched a new range of compact LED products known as the Luxeon Rebel family as shown in Figure 8. A significant advantage of the Rebel family is its very small form factor making it significantly easy to place multiple Rebels close together unlike many recent high power LEDs. Figure 9 compares the Rebel with other popular high power LEDs and its 3mm x 4.5mm makes it the smallest surface mount LED of its type. The small package coupled with high luminous flux enables the Rebel to claim the highest light density (at 1185 lumens per cm2 equivalent) and the highest packing density.
In an interesting departure from standard LED manufacturers information, the Rebel datasheet provides useful lifetime data at various forward currents and LED junction temperatures enabling a fixture design engineer to easily determine the performance of fixtures based upon the Rebel (see figure 10). It is hoped that by providing such data other leading LED manufacturers will follow thereby enabling engineers to design fixture to real life operating parameters.
Multi-Chip High PowerLED emitters
During 2007, further advances in multi-chip emitters within a single package were starting to deliver high power solutions to the lighting designer. In February OSRAM announced the new version of OSTAR Lighting that delivered more than 1000 lumens in cool white. The high-flux LED was equipped with six closely packed 1 mm2 high-power chips enabling a single OSTAR emitter combined with a 38° reflector to illuminate a desk with more than 500 lux from a height of two meters. OSRAM also claims that the OSTAR sets a new standard for a multi-chip solution by producing 75 lm/W from an operating current of 350 mA. Figure 11 shows the new OSTAR LED emitter from OSRAM.
Taiwanese manufacturer, Edison Opto Corporation, launched its cost-effective single 50W white LED during 2007 in a package size of just 30mm x 30mm. The 3300 Lumen output LED achieved 67 lumens per watt efficacy at a correlated colour temperature of 6500K from its initial launch of 2000 lumens corresponding to 40 lumens per watt. The future for multi-chip high power LEDs appears to be very bright according to Edison’s roadmap highlighted in figure 12. Edison appears to be very close to matching the efficacy performance predicted in 2006 with actual production values.
It is anticipated that Edison will launch a 100W version of its cool white LED tile during 2008 within the same package format delivering approximately 6000 lumens! It is envisaged that this type of product will be specifically aimed at the street lighting market

Improved white LED light: just what the lighting designer ordered

During 2007 the LED industry has responded to the requests from the lighting industry to produce white LEDs that are consistent in colour temperature. For example, Lexidis Lighting, a joint venture company between TridonicAtco of Austria and Toyoda Gosei of Japan launched the new XED LED free from any colour binning issues. LEXEDIS claim to have eliminated once and for all the cumbersome colour binning by improving it production process capabilities.
LEXEDIS defines the quality of its chromatic products using the MacAdam metric implemented worldwide by fluorescent manufacturers with the XED being rated as 6-step MacAdam. A MacAdam ellipse is the region on a chromaticity diagram which contains all colours which are indistinguishable, to the average human eye, from the colour at the centre of the ellipse as shown in Figure 13.
Although, other LED manufacturers such as Philips Lumileds do not specify the consistency of their white LEDs using MacAdam ellipses they have responded to the industry need by significantly improving the resolution of their binning structure as shown in Figure 14.

1A LED drivers

As discussed earlier, the trend for increased forward current in the new 2007 LEDs has meant a new generation of LED drivers were needed. Unfortunately, this is one particular area within the LED industry which needs more research effort as the number of quality LED drivers able to control LEDs up to 1A has been slow to emerge.
However, one company (Integrated System Technologies) launched a novel three channel controller in June 2007 that is capable of driving up to 210 watts of LED at up to 1A forward current. Impressively the compact iDrive-1000 LED driver shown in figure 15 does not require a large case and is 85% efficient enabling it to operate without a fan. Boasting dual thermal protection for both the driver and LED fixtures attached, the iDrive 1000 offers an industry first by enabling the lighting installer to choose the maximum forward current independently on each of the three channels from 500mA to 1A in steps of 50mA. This feature enables the iDrive-1000 to match exactly the maximum rating of a particular lighting fixture or to allow different rated LEDs on each of the channels. Further intelligence enables the driver to compensate for the voltage drop over long cable runs and for the increased LED forward voltage when driving LEDs at up to 1A.

In last December’s article I predicted that 2007 would see the development of the first 150lm/W white LED and the first 200+ lumen from a single LED and both were achieved!
This year, I predict that the industry will see the first 500 lumen single chip white LED in production, a 1 watt LED that exceeds 120 lumens per watt efficacy and the first 2 Amp (standard) rated LED.
These predictions are based upon the continued breakthroughs in LED emitter performance during 2007 which has led to increased performance of White LEDs and more importantly overcoming many of the previous barriers that held them back from the significant general lighting market. The increase in total luminous flux, reduction in package size and high quality consistent white LEDs are now set to ensure that LEDs displace CFLs within the next two years.
I believe that, although standards are required, the pace of LED development will circumvent minimum government energy efficiency legislation such as Part L2 of the building regulations or Title 24 even for badly designed LED fixtures thus increasing the pressure on standard bodies to get their act together.
No doubt many government departments will bring in subsidies to help stimulate LED adoption within the market place but care needs to be taken to ensure any criteria set is regularly updated to ensure subsidies are provided to only the top quartile of LED fixtures available on the market. Remember setting an absolute limit is foolish if the technology increases in efficiency so quickly!


Figure 1: The increase in White LED efficacy until 2012 from Cree

  • Figure 2: The increase in efficacy of Red and Blue LEDs as demonstrated by OSRAM

  • Table 1: Comparison of LED efficacy against traditional light sources

  • Figure 3: The lumen efficacy of an LED and the power consumed to generate 800 lumens of white light

  • Figure 5: The typical LED efficacy from various single chip White LED emitters

  • Figure 6: The latest efficiency gains from Philips Lumileds achieved at higher forward currents

  • Figure 7: The high current Diamond Dragon from Osram

  • Figure 8: The new compact Luxeon Rebel

  • Figure 8b: A schematic view of the Luxeon Rebel

  • Figure 9: A scaled comparison of the Rebel against similar high power LEDs

  • Figure 10: Luxeon Rebel lifetime data

  • Figure 11: The new 6-chip OSTAR from OSRAM

  • Figure 12: Edison Opto 50W roadmap showing predicted and actual efficacy trends

  • Figure 13: A chromaticity chart with various MacAdam ellipses plotter

  • Figure 14: The new Philips Lumileds white LED binning structure

  • Figure 15: The new three channel 1A iDrive-1000 LED driver from IST

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