White LED for General Illumination Applications
by
Ken, Li Fung Yuen
B.E., Materials Science and Engineering
Nanyang Technological University, 2006
Submitted to the Department of Materials Science and Engineering
in Partial Fulfillment of the Requirement for the Degree of
Master of Engineering in Materials Science and Engineering
at the
Massachusetts Institute of Technology
September 2007
© 2007 Massachusetts Institute of Technology
All rights reserved
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White LED for General Illumination Applications
by
Ken, Li Fung Yuen
Submitted to the Department of Materials Science and Engineering
on Aug 03, 2007 in Partial fulfillment of the
requirements for the Degree of Master of Engineering in
Materials Science and Engineering
Abstract
In the 21st century, mankind faces problem of energy crisis through depletion of fossil
fuels as well as global warning through the production of excessive greenhouse gases.
Hence, there is an urgent need to look for new sources of renewable energy or ways to
utilize energy more effectively. Solid state lighting (SSL) is a major area of research
interest to use energy in a more efficient manner. Early light emitting devices (LEDs)
were originally limited their use for low power indication lights. Later research produces
high brightness LEDs (HB-LEDs) as well as blue color LEDs. This brings to reality of
the entire visible light spectrum. White light is also made possible. As with other
technologies, numerous obstacles will have to be surmounted in bringing LEDs from the
laboratory to the marketplace. LEDs will also have to compete with established
technologies such as incandescent and fluorescent lighting. This thesis will describe the
current state of high powered LEDs, examine challenges faced by LEDs and look at
future markets. Evaluation in the potential of LEDs for general illumination will be
carried out through cost modeling and performance analysis.
Thesis Supervisor: Thomas W. Eagar
Title: Professor of Materials Engineering and Engineering Systems
Acknowledgements
I would like to express my gratitude to my M.Eng thesis advisor ProfThomas W. Eagar
from MIT for his hospitality, patience, constant guidance and care throughout the thesis
project. Moreover, I would also like to thank Prof Eagar for selecting me as his thesis
student by giving me such a great learning opportunity and exposure.
I would like to thank my thesis co-advisor Assoc. Prof Wong Chee Cheong from NTU for
his helpful guidance and suggestion for the thesis.
Beside, I would like to thank my wife, Michelle for her understanding, support and care
throughout the thesis project.
I would also like to extend my sincere appreciation to:
* Dr. John Desforge, Ms. Jocelyn Sales and Ms. JulianaChai from SMA Office for
their support and assistance.
* SMA AMM&NS 06/07fellow classmates for their company and encouragement.
Table of Content
Chapter 1 Introduction ...............................................................................
.............
5
1.1 B ackground ......................................................................................................
..............................................
1.2 M otivation .....................................................
1.3 Scope of thesis..................................................................................................
5
6
8
Chapter 2 White LED for general illuminating technology...........................
...... 9
2.1 Current technologies for general illumination .......................................... ......
2.2 White LED technology......................................................................................
2.3 Structure and fabrication technique of white LEDs ......................................
2.4 Advantages and limitations ..................................................................................
2.5 The future of white LED as general lighting devices............................. ....
Chapter 3 White LED Market Analysis ..................................................
9
10
14
18
19
21
3.1 LED s M arket .................................................. ................................................... 21
..........23
3.2 LED manufacturers & Intellectual property...............................
Chapter 4 Barriers and Issues for general illumination..........................
.........26
4.1 C ost barrier ............................................................................................... ............ 26
28
4.2 Efficiency barrier .....................................................................................................
4.3 Color quality barrier ............................................................................................ .31
4.4 D urability barrier.............................................. ................................................. 35
37
4.5 Thermal Management barrier ...................................................................
Chapter 5 Cost of Ownership Modeling and Performance Analysis ............................. 41
41
5.1 Cost of Ownership Modeling ...................................................
5.2 Performance Analysis ....................................................................................... 43
............ 45
5.3 Strategy for market penetration of SSL...................................
Chapter 6 C onclusion........................................................................................................ 50
Appendix I Simplified ownership cost model...............................
...........
51
Appendix II Summary of Government initiatives from various countries .................... 53
Chapter 1 Introduction
1.1 Backaround
Solid state lighting (SSL) in the form of inorganic compound semiconductors known as
light emitting diodes (LEDs) is perhaps the most significant advance in illumination since
the invention of the light bulb by Thomas Edison more than a century ago. The term
"solid state" refers to the fact that light in an LED is emitted from a solid object - a block
of semiconductor - rather than from a vacuum or gas tube, as is the case in traditional
incandescent light bulbs and fluorescent lamps. LEDs are a truly disruptive technology
providing a serious alternative to conventional lighting technologies in many applications
because they can create visible light with virtually no heat or parasitic energy dissipation.
Besides, the solid-state nature provides for greater energy efficiency, resistance to shock,
vibration, wear, and increased lifespan. Hence, SSL is a pivotal emerging technology that
promises to fundamentally alter and improve lighting systems of the future.
With the collaborative efforts of government and industry in moving this promising
technology from the laboratory to the marketplace, SSL is expected to start competing
with conventional light sources for market share in general illumination applications.
In 1907, H.J. Round discovered that when he applied a large voltage (>100V) to a SiC
crystal, light was generated from the transformation of electrons into photons which was
named electroluminescence. In the 1960s, electroluminescence was studied extensively
on III - V semiconductor alloys such as GaAs or GaAsP. In 1962, the first visible red
emitting LED was made of GaAsP. In 1968, the first commercial red GaAsP LED was
introduced to the marketplace by Hewlett Packard. However, the defect density has great
influence on the performance of such LEDs; the higher the defect density the lower the
light emitting efficiency.
In the 1970s, AlGaAs/GaAs single heterojunction diodes were proposed and developed.
By increasing the Al-fraction, AlGaAs/GaAs emission wavelength can be reduced to 660
nm (red). The AlGaAs bandstructure becomes indirect* at high Al-fractions, therefore it
is not possible to fabricate AlGaAs LEDs emitting at wavelengths shorter than 660 nm.
The next advancement was the introduction of double heterostructures which have better
confinement of electrical carriers in the active region of the device.
Subsequently, to get emission wavelengths less than 660nm, the AlGaInP system was
investigated intensively. The quaternary composition of AlGaInP allowed the bandgap to
be tuned from red to yellow and green while maintaining the same lattice constant.
To further reduce the emission wavelength, the material system of GaN was investigated.
In 1989, a Japanese group solved the problem of p-doping in GaN by activating Mg
dopants with low-energy electron-beam irradiation. Nichia Chemicals brought the first
commercial blue GaN-based LEDs to the market in 1994. By adding Indium to form the
InGaN alloy, Nichia fabricated the first blue-green (500 nm) and green (520 nm) LEDs.
With advancement in materials science and extensive research, development and creation
of high-brightness LEDs (HB-LEDs) that operated across the entire visible spectrum,
including blue and white LEDs, SSL has become a commercial reality to replace
conventional lighting and therefore, we have entered the solid state lighting era.
1.2 Motivation
As the world's population and standard of living increases, the demand for energy is also
increasing. Concern about terrorism and unrest in the Middle East, the largest source of
* GaAs is a compound semiconductor which has a direct bandgap for electron-hole pair generation and
recombination. Indirect bandgap semiconductors are inefficient in emitting light. See chapter 2.2 Principles
of LED for more details.
oil, has caused the cost for energy to increase as well. The mounting evidence of rising
carbon dioxide levels and global warming imply that all countries should be seeking
solutions for energy dependency on oil and natural gas. Strategies for meeting this
challenge include building new nuclear power plants, renewable energy sources and
reducing the consumption of energy.
Replacing conventional lighting with energy efficient SSL is an approach for reducing
the consumption of energy. Unlike conventional lighting devices, most of the energy
generated is dissipated as heat and little energy converts into light for optical illumination.
SSL consumes less electricity with less heat dissipation. According to a recent study in
U.S, potential benefits are enormous if SSL can achieve competitive price and
performance characteristics anticipated under an accelerated research investment scenario.
The study predicts that SSL could displace general illumination light sources in the next
20 years and decrease U.S national energy consumption for lighting by 29 percent and
save 3.5 quadrillion BTUs of primary energy'. It also estimates more than forty 1000MW
power plants would be deferred, contributing to a cleaner environment. Besides, LED
light sources have considerable advantages over traditional light sources such as
extremely long life, high durability and robustness.
Potential pitfalls to the widespread adaptation of SSL devices include light quality,
lighting fixture issues, general consumer resistance and high initial installation cost.
However, as the technology improves still further, the performance of LEDs will
continues to improve while prices decline. SSL will finally revolutionize the general
lighting market. Therefore, in this project, the focus is on the evaluation of the potential
of this new SSL technology to replace conventional lighting devices.
1Energy Savings Potential of Solid State Lighting in General Illumination Applications, Building
Technologies Program, Office of Energy Efficiency and Renewable Energy, US DOE.
7
1.3 Scope of thesis
The project aims to evaluate the potential of white LED for general illumination
applications. The objectives of this project are:
*
To gain an understanding of current white LED technology
*
To investigate barriers of SSL technology for general illumination application
*
To evaluate the adoption potential of SSL technology
Chapter 2 White LED for general illuminating technology
2.1 Current technologies for general illumination
Incandescent light bulb
The incandescent light bulb is a source of artificial light that works by heating a solid
filament to high temperature which causes thermal radiation including a large amount of
visible light. The first incandescent bulb was invented in early 1800s but suffered from
short service lifespan, and was modified by Edison in late 1800s with longer lasting
tungsten filaments.
The enclosing glass bulb prevents oxygen in the air from reaching and causes oxidation
of the hot filament. Although the incandescent light bulb produces color rendering index
(CRI) close to sun light, the incandescent bulb wastes power by emitting too much light
outside of the visible spectrum which is not for illumination purposes. Approximately
95% of the power consumed is emitted as heat, rather than as visible light.
Fluorescentlight
A fluorescent lamp is a gas-discharge lamp which was first invented by Heinrich Geissler
in the late 1800s. It was then commercialized by General Electric in the mid-1900s to
compete with the incandescent light bulb for lighting purposes.
A fluorescent tube uses an electric discharge in mercury vapor to produce ultraviolet (UV)
light, which is then transformed into visible light by fluorescent phosphors on the inner
surface of the tube. The blend of phosphors controls the color of the light produced, and
prevents harmful UV light from escaping.
Fluorescent lamps are more efficient than incandescent light bulbs due to a smaller
proportion of the energy being converted into heat. However, the CRI produced is lower
than incandescent light bulb. One of the major disadvantages is its mercury toxicity,
governmental regulations require special disposal of fluorescent lamps. However,
because of the ability to save energy, it is widely used for illumination in schools and
commercial sectors.
High-intensitydischarge (HID)
A gas discharge lamp uses an electric discharge in a gas inside the lamp to produce
visible lightly directly. Light is produced by striking an electrical arc across tungsten
electrodes housed inside a specially designed tube. This tube is sealed and filled with
both gas and metals. Gases used for HID lamps mainly include mercury vapor, metal
halide, high- and low-pressure sodium. HID lamps produce high quantity light and are
widely used in illuminating large areas such as warehouses, outdoor activity areas,
roadways, etc.
2.2 White LED technolovy
Principlesof LED
A LED is a semiconductor device that emits nearly monochromatic light. The LED
consists of n- and p- type semiconductors forming a p-n junction where electrons and
holes are injected. The LED generates light via the excitation of an electron into a higher
energy state and the relaxation of the excited electron back to the lower energy state after
combining with hole. The
conversion of electrons
into photons is called
electroluminescence. The emission wavelength can be tailored from infrared to
ultraviolet by using different semiconductor materials.
The band structure of the semiconductor material can be either the direct band structure
or the indirect band structure. In the direct band structure, the relaxation of the excited
electrons from the conduction band into the valence band can occur under momentum
conservation, while for the indirect band structure, the relaxation process needs the
assistance of phonons to achieve momentum conservation. Indirect band relaxation is less
probable.
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Figure 2.1 (a) Direct bandgap band-band transition 2.1 (b) Indirect bandgap bandband transition2
The relaxation of the excited electrons from the conduction band into the valence band is
characterized by the recombination rate of electrons with holes. The recombination rate is
proportional to the density of electrons, the density of holes, and a proportionality factor
which is a measure of the probability of the recombination.
Other than the band to band transition, there are several other mechanisms like: 1) band
to impurity level transition, 2) donor states to acceptor states transition, and 3) Auger
recombination process. The first two transitions are similar to the band to band transition
but the Auger recombination process is undesirable. For Auger recombination, the energy
2 Visible
light-emitting diodes by Klaus Streubel
released during electron hole pair recombination may be transferred to other carriers and
can then be dissipated as phonons instead of generating photons.
The center emission wavelength of an LED can be obtained by the bandgap energy
X=hc/Eg. By using high doping levels or graded substrates, the linewidth of the emission
spectrum can be increased. For all LEDs that use band to band transitions, the emission
spectrum measured at the top differs from the emission spectrum measured on the side.
The efficiency of light generation inside an LED is very high (>90%), however the
extraction efficiency of light from the semiconductor material is only a few percent. This
is because the semiconductors' refractive index is in the range of 3 to 3.5 while the
surrounding medium has a refractive index in the range of 1 to 1.5. As a result, the
interface of the semiconductor and the surroundings becomes a good reflection plane to
prevent the light coming out from the semiconductor material. Nowadays, individually
shaped dies are being employed to solve this light extraction problem for HB-LEDs.
White LED
The discovery of wide bandgap InGaN-based semiconductors has enabled the LED to
emit white light. The group III nitrides allow the generation of UV, blue, green and white
light. Theoretically, the InGaN-based semiconductors can cover a wide wavelength range
up to 630nm.
The most common way to achieve white LED light is by adding an inorganic phosphor
like yttrium aluminum garnet (YAG) doped with rare earth elements such as cerium (Ce)
into a blue LED. By adjusting the amount of phosphor powder in the LED die, different
correlated color temperatures (CCT) and CRI can be achieved. Therefore, it is important
to have consistent phosphor deposition during the packaging process in order to have
consistent white LED products. Nevertheless the emission light appears to be bluish or
cold white due to the low level of absorption in the phosphor. Moreover the CRI is
relatively low since there is only yellow and blue with no red color (see Figure 2.3).
Another common method is to use Red + Green + Blue (RGB) LEDs in order to produce
white light but this multiple chip approach has the disadvantage of large unit area,
multiple connections as well as higher cost. Each LED must be controlled properly by
separate circuits in order to have proper white light generation.
(a)
(b)
Figure 2.2 (a) White light generated by phosphor extraction 2.2 (b) White light
generated by color mixing
In order to generate high-performance white light, a white LED can also be made by
incorporating a two- or three-color phosphor into a near UV LED. For instance, this is
done by coating the near UV LED with red and blue phosphors plus aluminium doped
zinc sulfide and green emitting copper. Currently, Yuji Uchida and Tsunemasa Taguchi
have developed orange (0), yellow (Y), green (G), and blue (B) white LEDs consisting
of OYGB phosphor materials and a near UV LED3 .
3 Yuji Uchida and Tsunemasa Taguchi, Lighting theory and luminous characteristics of white light emitting
diode
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Figure 2.3 Spectrum of white LEDs (a) RGB LED (b) UV LED with RGB phosphor
(c) Blue LED with yellow phosphor
White LEDs using no phosphors are also being researched. This technology is based on
homoepitaxially grown zinc selenide (ZnSe) on a ZnSe substrate and quantum dot white
LEDs.4
2.3 Structure and fabrication technique of white LEDs
LED device structure
Commercial LEDs normally consists of three parts: the semiconductor die as the light
emitting diode, a mounting substrate and the encapsulation resin. Figure 2.4 below shows
a cross-sectional view of a typical white LED device.
4 http://en.wikipedia.org/wiki/LED
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died
The white LED die consist of a GaN lighting emitting diode, such as an n-type layer, a ptype layer or an active layer, which is allowed to grow on a sapphire substrate, by way of
Metal Organic Chemical Vapor deposition (MOCVD) or the Molecular Beam Epitaxy
(MBE), this forms a light emitting diode section. The n-type and p-type layers or the
active layer maybe formed by using a GaN compound such as GaN, InGaN, AlGaN or
AlInGaN. Additionally, the active layer may have a single quantum well (SQW) structure
or a multiple quantum well (MQW) structure.
It is possible to provide various light emitting diodes ranging from a short wavelength to
a long wavelength by controlling the composition of the GaN compound with the
bandgap of the semiconductors. Blue light is generated which is essential for producing
white light for general illumination.
The mounting substrate may comprise material such as CuW, metals including Al and Cu,
Si wafer or AIN ceramics. Generally, sapphire is widely used to grow the GaN-based
compound semiconductors for use in the manufacture of LEDs due to their high melting
temperature, lattice matching, and their high strength for device support. There are two
methods for mounting a chip in an LED package.
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Figure 2.5 (a) conventional chip-up mounting (b) flip-chip mounting
The conventional method is chip-up mounting (see Figure 2.5a), in which the active light
emitting p-layer of the chip faces up, and the substrate is attached to the heat sink.
Alternatively, there is chip-down (flip-chip) mounting, in which the active p-layer of the
chip faces down (Figure 2.5b). Light is reflected up from the epilayer-substrate interface.
The flip-chip approach enables superior heat sinking which may allow the phosphor and
encapsulant to remain cooler. Flip-chip also removes the wire bond from the top face and
reduces the absorption of light due to the wire bonding and contact layer. However, chipup has fewer processing steps which are less expensive to manufacture than flip-chip.
The LED chip mounted on sapphire is covered with a molding material such as epoxy or
a molding material containing a phosphor for down converting blue light to white light.
The molding material that may be used includes, but is not limited to epoxy, silicone and
arylic resins.
Fabricationtechnique of white LEDs
Referring to Figure 2.6, which shows a manufacturing process of a typical LED, the
complexities and steps can be varied between companies with different products.
Generally, the manufacturing process can be divided into the following steps:
GaN chip fabrication: Die fabrication includes GaN crystal growth, MOCVD or MBE
deposition of p-type, n-type and active layers, ohmic contact formation, dry etching and
surface polishing
Die Bonding: the LED chip is placed and bonded onto a lead frame
Soldering: A metal lead is made to connect the LED chips so to form an electrical link
Encapsulation: Upon injecting a thick, viscous, fluid epoxy resin into a mold, the LED
chips and lead frame is placed into a mold
Baking: Upon encapsulation, place encapsulant material is placed into a furnace and
heated to at high temperature for the resin to be fully hardened thereby completing
encapsulation
Cutting, testing and packaging: various testing is carried out to ensure the LED device is
functioning before shipping to the consumer
GaN chip fabrication
Die bonding
Soldering
Encapsulation & baking
Cutting, testing & Packaging
Figure 2.6 Flow chart of LED manufacturing process
2.4 Advantages and limitations
SSL sources have considerable advantages over traditional lighting sources such as
extremely long life, high durability and low energy usage, SSL provides a variety of
colors due to their unique nature. In addition, SSL engines are fully dimmable and can be
controlled by something as simple as a switch or as sophisticated as a computer linked
via the internet. Existing lighting technologies simply cannot compete with the huge
number of design, control and display possibilities available with SSLs.
Although there are many beneficial reasons, SSL has limitations as well. Currently, they
are relatively more expensive in cost per lumens, on an initial capital cost basis, than
traditional lighting technologies. Moreover, the lumen per watt of current SSL
technologies is still similar to fluorescent lighting. Further enhancements are required to
improve SSL before replacing traditional lighting.
Performance of LEDs largely depends on the ambient temperature of the operating
environment. Improper high temperature operating environment will affect LED
performance as well as shorten its service life, eventually leading to device failure. To
maintain long service life, adequate heat sinks are required for heat dissipation. This is an
extremely important consideration when devices have to be operated over a large range
of temperatures. LEDs have to be supplied with the proper level of current during
operation. It is necessary to have individual resistors or regulated power supplies when
parallel connection is required. Moreover, the light emitted from LEDs typically has
narrower angles compared to an incandescent or fluorescent lamp of the same lumen
level.
Currently, the spectrum of the emitted light from white LEDs differs from a black-body
radiator, such as incandescent light, which causes the color of objects to be perceived
differently. The white light produced also falls outside the natural range, making them
less suitable for domestic lighting.
2.5 The future of white LED as eeneral lighting devices
Over the past forty years this compound semiconductor-based light source has evolved to
become a bright, efficient source of white, red, green and blue light that is giving cars,
interior lighting and signage a radical new look. LEDs have successfully penetrated low
power lighting applications such as indicator lamps, automotive and display applications.
As the technology improves, the performance of HB-LEDs will further decrease their
price. The powerful combination of these two factors means that makers of HB-LEDs are
now preparing to tackle their next big market opportunity - the general illumination
market.
Today, the two main disadvantages that white LEDs must overcome to achieve widescale adoption in the general lighting market are their much higher cost compared with
traditional light sources, and their low light output per emitter. Both of these problems are
being vigorously addressed by the LED industry, and substantial progress is being made.
Historically, the price of light generated by LEDs (measured in dollars per lumen of light
output) has declined by a factor of 10 per decade, whereas the light output from a single
device has increase by a factor of 20 per decade. This trend is called Haitz's Law (see
Figure 2.7) and can be thought as an analogy of Moore's law, which charts the speed
increase and size decrease of silicon microelectronics. In fact, since 2002, the lumen
output of the best commercial white LEDs has increased by a factor of six, and the cost
per lumen has decreased by a factor of seven. Nevertheless, yet more progress is required
before LEDs can effectively penetrate the large-scale general illumination market.
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005
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Figure 2.7 Haitz's Law - the trend of LED progress5
The outlook for the use of LEDs in lighting is highly promising, as efficiency continues
to improve, prices continue to decline, and hundreds of companies around the world
develop lighting systems that used LEDs to address a wide variety of applications. With
the aid of governments pushing and expediting the usage of SSL, the global energy
consumption and environmental issues can also be addressed. It is also believed that solid
state lighting technology is expected to outperform first incandescent and later
fluorescent lighting in the next decade for general illumination.
5 Source from Roland Haitz and Lumileds
Chapter 3 White LED Market Analysis
Having introduced an overview of LED technology in the previous chapter, we will now
look at the current market status and future forecast of white LED technology. At the
same time, leading LED manufacturers and their strengths will be discussed briefly.
3.1 LEDs Market
Rapid improvement in HB-LED technology has opened up the possibility of using LEDs
as sources of general illumination in the near future. Remarkable progress in efficiency,
lifetime, and total lumen output has established an early market in niche lighting
applications. In year 2002, the HB-LED market reached $1.8 billion. It can be
conveniently divided into six major application categories, and associated subcategories.
These are given in table 3.1, along with figures showing the size of each market segments.
Table 3.1 potential applications of HB-LEDs and market size in year 20026
6 http://comoundsemiconductor.net/articles/magazine/9/12/2
Due to the low efficiency, usages are limited to low light output areas such as flashlights
and architectural lighting. As table 3.1 shows, the use of HB-LEDs in illumination
applications accounted for only 5% of the market ($85 million) in 2002 which is
relatively small. However, it is one of the fastest-growing applications, and the one that is
driving a great deal of current interest in HB-LED technology.
b
a
Figure 3.1 HB-LED market in (a) 2005 (b) 2010
While intensive research and development has taken place, the improvement in HB-LED
technology is increasing the market penetration and is starting to replace conventional
lighting technologies. From Figure 3.1, we can see that the HB-LED market rose from
1.82 billion in year 2002 to 4 billion in year 2005, and is predicted to further increase to
about 8.2 billion in year 20107. Of these HB-LED revenues, approximately 6% or $250
million and 13% or $1 billions are attributable to illumination applications in 2005 and is
predicted for year 2010 respectively. Thus, general illumination is thought to be one of
the greatest potential major markets for HB-LED technology in the near future.
7 Strategies in Light, 2005. High Brightness LED Market Review and Forcast - 2005. July 2005.
22
In year 2005, the total lighting product sales in the U.S are worth about $13 billion
annually. Within this value, sales of lamps are about $2.45 billion while the remaining
sales are divided into fixtures, components and lighting services such as design and
maintenance 8. Therefore, there is plenty of room for SSL to be improved and expanded to
replace conventional lighting.
3.2 LED manufacturers & Intellectual property
There are hundreds of LED manufacturers and distributors in the current LEDs market9 .
Some of the major existing players are listed below:
U.S: Cree; Philips Lumileds Lighting; Avago Technologies
Japan: Nichia, Citizen, Toyoda Gosei, Stanley Electric, Rohm
China: Cotco (Hong Kong), Lumei Optoelectronics, Sanan
Taiwan: Epistar, Epitech, Formosa Epitaxy, Everlight, Lite-On, Kingbright, Harvatek,
AOT
Korea: Seoul Semiconductor, Samsung Electro-Mechancis, LG Innotek
Europe: OSRAM Opto Semiconductors
Company
Patent No.
Filing date
Nichia
5.998,925
Jul-29-1997
Lumileds lighting
6,603,258
Publication
dates
Dec-07-1999
Brief Description
GaN LED with phosphor garnet
fluorescent material
Apr-24-2000
Aug-05-2003
LED device that emits white
light with a phosphor powder
Cree Lighting
Company
6,885,036
Jun-25-2003
May-06-
Scalable LED with improved
2004
current spreading structures
Table 3.2 Major patents from various companies
8Statistics for Industry Groups and Industries: 2006. Economics and Statistics Administration. U.S. Census
Bureau. November, 2006
9The Market for High-Brightness LEDs in Lighting: Application Analysis and Forecast -2007
http://downloads.pennnet.com/pnet/research/66/su_ledfront_toc.pdf
23
As reported, manufacturers Nichia, Lumileds, Osram, Toyda Gosei, and Cree are the few
leading players in the HB-LED market. Table 3.2 shows some of their key patents. The
value of these patents in covering the aspects of LEDs fabrication as well as the
performance attributes that are achieved through these means is to prevent competing
companies from using their technologies without paying a licensing fee.
Since Nichia first produced white LEDs commercially in the mid 1990s, the background
and history of SSL development is surprisingly complicated. There are numerous patents
and most of them are about the phosphors used to extract white light. There are extremely
complicated relationships, overlap, and conflicts among the US patent. Thus, disputes
and cross-licensing, agreement and partnership corporations have been formed between
the major HB-LED players. Figure 3.2 shows the complicated disputes and intellectual
property relationships of the HB-LED industry. Table 3.3 summarizes the strength of
various LED manufacturers for comparison.
Figure 3.2 Disputes and intellectual property relationships of HB-LED market in 200510
10 http://www.china-led.net/Html/news/zljj/2007-2/9/134218763.htm
24
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Table 3.3 Strength comparisons of HB-LED manufacturers"
" Advances in LED Energy efficient lighting technology 2005
Iat
Chapter 4 Barriers and Issues for general illumination
In the previous chapter, the major LED manufacturers worldwide as well as the HB-LED
forecast markets were analyzed. Though the market of HB-LEDs is expected to be big
and LEDs are expected to replace conventional devices for general illuminating
applications in the foreseeable future. SSL is still not commercially viable for general
lighting applications. Various technological hurdles are to be overcome first before
significant penetration occurs. In this chapter, major barriers such as cost efficiency,
color quality, durability and thermal management will be discussed.
4.1 Cost barrier
The high cost of LEDs is the main barrier preventing them from replacing conventional
lighting devices. In year 2005, the price of LED lamps is about 10 times more expensive
than the incandescent bulb and slightly higher than fluorescent lighting due to the high
manufacturing cost of solid state semiconductor devices. Besides, the luminous flux of a
LED lamp is 6 times less than an incandescent and 20 times less than fluorescent lamps.
The high price and poor performance prohibits the wide use of LEDs for general lighting.
Although the cost of LED light sources has dropped dramatically in the past few years, it
is still far greater than that of conventional light sources. However, with the
improvements in performance and continual price drop over the next few years as
predicted by Haitz's law (see in chapter 2), LED light sources will become more
competitive with conventional light sources.
The typical electrical energy required for LEDs is less than that for conventional lighting.
Consequently, the energy savings and operating costs of LEDs in comparison to
conventional lighting is lower. In addition, the longer durability of LEDs compared to
conventional lighting may mean that the cost per unit lifetime is lower than that of
conventional lighting although the initial price is higher. Life-cycle cost, the lower cost in
ownership (measured in the unit of $/Mlm.hr) can be estimated by including lamp cost,
energy consumption and maintenance over the lighting service period. The cost of
ownership can be estimated as following:
Cost of ownership = Capitalcost + Operatingcost
Cownershp = 10 6 X (CB +CM /
(Px xr) + 103 x (CE / )
(Eqn 4.1)
(Eqn 4.2)
Cownershqp = Cost of ownership ($/Mlm.hr)
CB
= Cost of lamp ($)
CM
= Cost of maintenance cost ($)
CE
= Cost of electricity ($/kWh)
P
= Power of Lamp (W)
r
= luminous efficacy (lm/W)
T
= durability of the lamp (hr)
LED-based SSL is already an alternative for many applications such as traffic lighting
and automotive lighting. For instance, although incandescent lamps have lower lamp
costs and higher lumen output than current LED, LED sources have much longer
durability and consume less power. If we use the equation above and look at the cost of
ownership over a period of few million lumen hours, the LED has slightly cheaper cost of
ownership per unit time compared to incandescent light sources.
However, the higher initial capital cost will still be a determinant for consumers to
purchase LED technology. This is especially so when the performance of LEDs has yet to
compete with conventional incandescent and fluorescent lighting.
On the other hand, the penetration of LED in the lighting market depends on the
sensitivity of customers on the payback rate of LED technology over conventional
lighting. The saving potential in the residential area may not be too significant. However,
in the case of the commercial sector, the larger consumption of energy in illumination
will contribute to significant cost savings and shortened payback time. Thus, the adoption
of cost effective LED technology is expected to be more prevalent in the commercial
sector compared to the residential sector.
Nevertheless, as technology continues to improve, the cost of LEDs will continue to drop.
As the manufacturing process reaches maturity, market growth of LEDs in the arena of
general illumination is expected to speed up due to the advantages of LED based
technology.
4.2 Efficiency barrier
The main driver of SSL for general illumination is the significant saving in energy
consumption. Currently, the energy efficiency of HB-LEDs is expected to be higher than
those conventional light sources and it shows that there is plenty of room for further
improvement in efficiency of LED technology.
The energy efficiency of lighting devices is typically measured in lumen per watt (lm/W).
This is the amount of light output for each watt of electric power consumed. This is also
known as luminous efficacy@. The table below shows efficiency comparisons between
current LED technology and conventional lighting sources. It can be seen that the
efficacy of LEDs has already surpassed incandescent light bulbs but has yet to compete
with fluorescent based lighting devices in terms of efficiency. Also note that the
technology and luminous efficacy of warm white LEDs are lower than "cool" white LED.
0 Luminous efficacy - the total luminous flux emitted by the light source divided by the lamp wattage;
expressed in lumens per watt (hm/W). Efficacy - the term efficacy normally used where the input and
output units are different where efficiency usually is dimensionless and usually is used for broader concept
of using resources efficiently. In measuring the efficiency of light sources, the amount of light produce is in
lumen (lm) and the input power is in Watt (W), the term luminous efficacy is used.
28
..
.. . .........
.
(varies depending on w attage and lamp type)
Incandescent
10-18
Halogen incandescent
15-20
Compact fluorescent (CFL)
35-60
Linear fluorescent (TS,TS)
50-100
Metal halide
50-90
.45-59*
White LED 5000K
Warm white LED 3300K
22-37"
*Current as of October 2006.
Table 4.1 System efficacies of various lighting devices
The LED system can be divided into 3 main parts namely driver, fixture and device. Each
of them accounts for the efficiency loss in transferring electrical power to useful light.
The figures shows below are the structure, current and target efficiencies of Blue LED
with phosphor conversion and RGB system based LEDs respectively.
Luminaire line
o
Io+
as%
Ee
200s
30%
T"Mget
81% 1
S 13% 1 6%
1010%1 %1
S70%
90%
F1WFi1
46%
8%
Figure 4.1 Current and target system efficiencies for Blue LED with phosphor
conversion
Ioos
Line voltage
F 75%T8G%
0
S
I
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O%B
9o%R
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60%8 9MB
Sso50%G
M 17% 166% 1
Tare
17%
66%
I
Figure 4.2 Current and target system efficiencies for RGB system based LED
It can be seen that the current total luminous efficacy are relatively low for both cases.
The main reason is due to low device efficiency, particularly in extraction efficiency (x.)
for both cases and internal quantum efficiency® of green color in color mixing based
LED. In the case of blue LEDs with phosphor conversion, the additional phosphor
efficiency accounts for the lower conversion efficiency, stokes shift loss' of the phosphor.
This is an unavoidable additional loss for blue LED with phosphor conversion.
As for the RGB system based LED, the additional color mixing efficiency refers to losses
incurred while mixing discrete colors in order to produce white light. Color mixing could
also occur in the fixture and optics. In this case, this color mixing loss is assumed to
occur in the device only.
OExtraction efficiency is the ratio of photons emitted from the encapsulated chip into air to the photons
generated in the chip. It includes the effect of power reflected back into the chip because of index of
refraction difference
9 Internal quantum efficiency is the ratio of the photons emitted from the active region of the device to the
number of electrons injected into the LED
* Stokes shift loss is thermal energy loss during fluorescence process. When a molecule or atom absorbs
light, it enters an excited electronic state. The Stokes shift loss occurs because the molecule loses a small
amount of the absorbed energy before releasing the rest of energy as luminescence.
30
These factors cause the overall efficiencies of current phosphor converting based LEDs
and RGB system based LEDs to as low as 8% and 9% respectively. Therefore, aggressive
research is needed to address these problems and meet targets so that SSL can be realized.
4.3 Color quality barrier
Color quality is one of the key challenges that LEDs face for general illumination. To
characterize the quality of a light source, Color Rendering Index (CRI) 12 and the
Correlated Color Temperature (CCT)' 3 has been widely adopted and used by the lighting
industry.
CRI is a specification to assist designers in making comparison between different lights
in appearance from a reference source. It indicates how well a light source renders colors,
on a scale of 0 - 100. It is related to the idea that if a red object is illuminated with red
light it appears red, but it appears grey or black if it is illuminated with blue light. The
color reflected and perceived will change with the color of the source used. The reference
source used is the sun (or a black body), and by definition it has a CRI of 100. Figure 4.3
shows the effect of different rendering index. It clearly shows that the higher the CRI, the
better will be the color quality.
CCT describes the relative color appearance of a white light source. It is given in Kelvin
(the unit of absolute temperature) and refers to the appearance of a theoretical black body
heated to high temperatures. As the black body gets hotter, its color turns red, orange,
yellow, white, and finally blue at higher temperature. The CCT of a light source is the
temperature (in K) at which the heated theoretical black body matches the color of the
light source in question. Generally, light sources with a higher CCT appear to be blue
http://en.wikipedia.org/wiki/Color rendering index
13http://en.wikipedia.org/wiki/Color temperature
12
and said to be "cool" light in appearance, while those with lower CCT are more yellowish
and characterized as "warm" light sources (see figure 4.4).
Figure 4.3 Object appears in different CRI
|:,
ltiti
Warm
Whte"
3500
350
I
1ma iU96
~ -44&
a
~~amim'4~m
4.h~
3fibmwa,
CW*00*0
MOLMMOME6
Owma, CRZS,4*
Figure 4.4 Object appears from sources with different CCT
As comparing with conventional lighting devices such as incandescent and fluorescent
lamps, LEDs are not inherently white light sources. Due to the working principle of direct
bandgap semiconductors in nature, the light produced by LEDs is nearly a
monochromatic light with a very narrow range of wavelengths in the visible spectrum.
This explains why LEDs are excellent for colored lighting applications. Thus, extra steps
are required to first convert these monochromatic lights into white light before
considering them for general illumination. Three methods to retrieve white color light in
the current trend are namely blue LEDs with phosphor conversion; UV LED with multichromatic phosphors conversion and RGB systems which have been discussed in chapter
2.
In the phosphor conversion method, predominantly YAG:Ce phosphors are used to make
white LEDs. The absorbed blue light (shorter wavelength) is re-emitted in the yellow to
red region (longer wavelength) of the visible spectrum to produce white light. This
conversion suffers from a loss of energy (known as the Stokes shift) which reduces the
overall device efficiency. This method would generally result in high CCT with "cool"
light and poorer color rendering appearance. The CRI and CCT can be improved if the
manufacturers can be tempted to use more phosphors but the trade off of using multiphosphors is further decreased in efficacy. The white light extraction of UV LED chips is
similar to the blue LED down-converting system, but has some important differences.
The UV light generated is completely adsorbed by the phosphors, down-converting to
RGB color and mix to produce white light. Due to scattering and adsorption losses in
multi-phosphors layer, it makes this method inherently less efficient than blue LED
down-converting system.
Another issue frequently raised by lighting manufacturers is the variation in color quality
within batches of white LEDs. The human eye is highly sensitive to differences in hue,
and can also perceive differences in intensity as a difference in color. The sensitivity that
generally can be detected as a color change by the human eye is on the order of 50K -
100K CCT. As a requirement for general illumination purposes, this quality assurance in
consistency has to be carefully controlled and improved before mass production and
market penetration. On the other hand, the color-mixing method is the most efficient way
to make white light from LEDs since there is no Stokes shift required' 4, and offers
infinitely graduated color and white color control. CRI can be excellent, >95, and CCT
can be controlled dynamically by an external detector plus feedback system for more
sophisticated usage. However, the major drawback is its increased complexity. It would
require multi-chip mounting and potentially sophisticated optics for blending the colors.
It may also require additional feedback circuitry to address the different degradation and
thermal characteristics of the discrete LED chips. As a result, phosphor-converted white
LEDs gives lower cost in manufacturing.
Nevertheless, each approach has certain advantages and disadvantages. The key tradeoffs are color quality, light output, efficiency and cost. Table 4.2 summarizes the
advantages and disadvantages from different approaches. Through the basic tradeoffs
between the three different approaches, the long-term winner is hard to predict. Most
currently available white LED products are primary blue LEDs with phosphor conversion
because they have higher efficiency and are simple in nature. RGB systems are more
often custom designed for more professional usage as architectural lighting.
1
4 R. Mueller-Mach,
G.O. Mueller, M.R. Krames, and T. Trottier, High-Power Phosphor-converted Lightemitting diodes based on III-nitrides, IEEE J. Select. Topics Quantum Electron., Vol. 8, pp. 339-345, MarApr. 2002
I
Near-UV LED + pM
r
*
a
A
Wimer color mperaiag
Warmer colorcmnperawres
I
isaantage
* LRa mawte lxhooloy
* Rlawntly low efficacy
Table 4.2 Comparison of White LED technologies
For comparison purposes, standard incandescent lamps typically have a CRI close to 100
and CCT of around 2700 with a warm light in appearance. Fluorescent lamps having
CCT between 2700K - 3000K and CRI > 75 are commonly used in commercial area for
illumination. Therefore, the trend of LED development is to improve color qualities such
that the CCT decreases to 2700K - 3000K to produce warmer light and having CRI >75
before substantial replacement of conventional lighting technology.
4.4 Durability barrier
All light sources will experience a decrease in the light output when they operate over
time, a process known as lumen depreciation. In incandescent light bulbs, the filaments
evaporate and the tungsten particles collected on the bulb wall over time. This decreases
the original lumen output by 10 to 15%. In fluorescent lamps, photochemical degradation
of the phosphor coating over time causes lumen depreciation as well. Figure 4.5 shows
the typical useful life for various light sources.
Typical Lumen Maintenance Values for Va ous Light Sources
-SOW
Tungsten Halogen
-*-.*42W CL
... 32WT1. F•h
uowwrc
50%
| 0~~
a--.54c-diwnLiED
,i·
HSjQO.pftb
LE
5a
o
s1oo
=0to
Iaooo
2Maoo
operating time (hr)
Figure 4.5 Typical lumen maintenance values for various light sources 15
Considering LEDs for general illumination, one of the main advantages is their
potentially very long durability. Significant maintenance cost savings as well as lower
servicing contributes to lower cost of ownership. Though the claimed lifetime for LEDs
can be as long as 50,000 hours or even 100,000 hours, the measured lifetime is much
shorter. The primary reason of LED lumen depreciation is heat generated at the activeregion. Since there is no infrared radiation emitted, the only way for LEDs to dissipate
heat is through either conduction or convection. The device will be degraded as a result
of overheating if the heat sinking or ventilation is inadequate. Continuous operation at
elevated temperature will cause permanent damage to the device and continue to lower
the light output. Thus, lumen depreciation becomes an important factor in determining
the effective useful life of the device.
Based on studies from the Alliance for Solid State Illumination Systems and
Technologies (ASSIST), the recommended useful life is defined as the point at which the
15Lighting Answer: LED lighting systems. Troy, NY. National Lighting Product Information Program,
Lighting Research Center, Rensselaer Polytechnic Institute
36
device light output has drop to its 70% of the original lumen (L70) for general lighting.
The requirement may differ depending on the application of the device, for some
applications, a higher level (>L70) may be required. In general, L70 is an acceptable level
for general illumination in office environment provided the depreciation process is
gradual and unnoticeable.
Therefore, electrical and thermal designs are also critical factors to improve both the
reliability and performance of LEDs system. Accelerated lumen depreciation may have
unwittingly added to consumer dissatisfaction and causes lost in confident of LEDs
technologies in the long term.
4.5 Thermal Management barrier
One of the important SSL attributes is input power density. Generally, the higher the
input power density the more lumens can be created per area of semiconductor chip. The
limits on input power density will depend on the ability of the device to extract heat from
the chip, and on the ability of the chip and the phosphor to maintain their conversion
efficiencies at high operating temperatures.
Increasing current density is the usual way of extracting more light power from one LED
so to have enough lumens for general illuminating purposes. However, there is a
limitation of light power density due to the overheating of active-regions, which increases
with operating current density. The other associated problem of overheating is that the
durability of LEDs is also strongly affected by active-region temperatures during
operation. At high temperatures, breakdown or failure can occur in some parts of the
LED or its packaging such as encapsulating epoxy melting.
Unlike conventional lighting devices, LEDs emit little or no infrared (IR) or ultra violet
(UV) radiation, but convert only 20-30% of the power into useful light. The rest of the
energy is thus converted into heat and has to be extracted from the chip through the
device to the surroundings.
Poor heat dissipation paths of the device could lead to overheating of the active-region,
thus, affecting both short-term and long-term performance of LEDs. The short-term
effects could be color shifting and reduced light output while the long-term effect could
be reduced useful life.
For phosphor conversion blue LED based light sources, the breakdown often occurs
when the glass transition of an encapsulating epoxy or lens is reached, causing loss of
transparency and melting of the material. Moreover, there are always dark spots on the
chip surface resulting from initial irradiative recombination defects. The size of these
dark spots will increase with time at high temperatures causing chip degradation.
As for RGB-based white light systems, the light output of different colored LEDs
responds to different operating temperatures. Among them, amber and red colored LEDs
are most sensitive to temperature changes and blue color the least (see figure 4.6 below).
These differences in temperature response will contribute to a noticeable color shift of the
light output if the operating active-region temperature differs from the designed
parameters. This leads to complexity and cost for manufacturing RGB-based white LEDs
for general illumination.
The measurement of luminous flux and color of LEDs devices by the manufacturers are
based on 25 millisecond power pulse method at a fixed active-region temperature of
278K. Thus, the active-region temperature is expected to be higher under continuous
current operation at room temperature condition. Therefore, inadequate thermal design of
LEDs could lead to lower light output, as compared to the manufacturing specification.
200%
0
100%
50%
0%
,40
.20
Source: PNNL
0
20
40
JuraonTempMR
60
80
100
120
urTtC)
Figure 4.6 Light output of colored LEDs at different active-region temperatures
Continuous operation at high temperature accelerates the lumen depreciation effect and
shortens the useful life of LEDs dramatically. The figure 4.7 below shows the light output
over time for three identical LEDs driven at the same forwarding current but with
different temperatures in the active region. The experimental data was obtained up to
10,000 hours and has been extrapolation beyond. The estimated useful life is defined as
70% of original light output decreases significantly with only 10K increases in active-
region temperature.
1•1
1.0
p
0.9
z
-
t
.
.......
.......
.......
610
0.8
04
i
i
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f
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.
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.
.
.
.
0.1
0.0
1,000
................................................................
..
. ...
10,000
100,00 0x
Hours
Figure 4.7 Useful life of white LEDs at different operating temperatures'6
It can be seen that heat management of LEDs is a crucial consideration to the design and
application for general illumination. There are three primary factors affecting the activeregion temperature of an LED, namely drive current, thermal path and ambient
temperature. Generally, the higher drive current will lead to greater heat generated in the
chip. Heat generated must be removed from the chip to maintain expected light output,
useful life and color. The amount of heat that can be removed depends on the ambient
temperature and the design of the thermal path from the chip to the surroundings.
Successful SSL will use excellent heat sink designs to dissipate heat, and minimize the
active-region operating temperature. Therefore, keeping the active-region operating
temperature as low as possible is necessary in order to maximize the performance
potential of LEDs.
16 Technology
White Paper, Understanding power LED lifetime analysis, Philips Lumileds Ptd Ltd
40
Chapter 5 Cost of Ownership Modeling and Performance Analysis
In the last chapter, we have discussed the major barriers and challenges faced by LED
technology for general illumination. Among these factors, cost effectiveness seems to be
most direct and easiest tool for performance comparison. The cost of ownership of SSL
will be estimated through simplified assumptions and performance over conventional
light sources. A practical strategy for SSL penetration is developed and purposed.
5.1 Cost of Ownership Modeline
Although cost of ownership might not be the best way to estimate the performance of
SSL over conventional light sources, it is the most appropriate method for comparison.
Based on the equation listed in chapter 4, a cost model is now put forward for estimating
the performance of SSL (see more details in appendix I). Table 5.1 shows the results of
ownership cost modeling.
Lamp cost (US$/kim)
Lamp cost (US$Ramp)
Maintenance cost
30.0
114
6.0
4.6
1.0
1.3
CRI
78.5
0.88
•.. i
.•..:...:.:..
...,....
0.42
1.47
3.1
S1.9
85
I00
75
0•20
1.25
0.18
4.38
U.52
~....2.5
4.0
1.5
82.5
:
"--
,0:: :7
180
... . .. .
Capital cost (U$S/Mimh)
Operation cost
(US$/MImh)
Ownership cost
(U-S$Mlmh)
1.75
0.74
045
I••:
...
.. . ••
........8
0.93
2.68:
.... .
0.58
.. .
1.32
. ....
0.44
0.47
''::~'i!•!:::iii:::
: IE:,!i:•
•:!•:••••i
:•i··••:
;•I•!•0.78
•:•
•a:••
1.00
"
................
..............................
r
i
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........
"
Table 5.1 summaries of simplified ownership cost modeling
41
••.:•:•.••..:
.•.••:. 0.U3
i i•:i..:..i.
It can be seen that the cost of ownership of SSL is US$ 2.68 in year 2005, and continues
to decrease to US$ 1.32 in year 2012, US$ 0.88 in year 2015 and finally projected to US$
0.47 in year 2020. If this scenario comes to pass, the ownership cost of SSL is already
lower than that of the incandescent bulb in 2007. It will be lower than that of Fluorescent
light sources by 2015, and much lower than all conventional lighting by 2020. The most
difficult task of any estimation of performance is to predict the occurrence of scientific
breakthroughs. Thus, simplifying assumptions are needed in order to gauge the
development of technologies in the future. In this case, aggressive development of SSL is
being assumed and it is by no means assured that it will come to pass.
SimplMed payback year sensitivity
I
l
1
2
3
4
.
.
.
.
5
6
7
8
0
10
Year
Residential -
Commedcal
Figure 5.1 Probability of acceptance comparison
As for this particular case of ownership cost estimation, a payback rate is required to
further estimate the penetration potential of SSL technology. Two kinds of scenarios, the
probability of acceptance from residential (incandescence only) and commercial
(Fluorescent only) sector for using SSL for general illumination, are being considered.
The commercial sector is expected to have higher probability of acceptance since the
energy saving are more significant resulting in higher cost savings. In contrast, residential
42
lighting has a lower probability of acceptance even though SSL has a lower cost of
ownership over conventional light sources. For the commercial sector, the scenario
assumes that approximately 60 companies out of 100 are willing to switch to SSL if the
payback rate is within 1 year and 40 companies out of 100 will switch if the payback rate
is within 2 years. On the other hand for residential, the scenario assumes that 30 people
out of 100 are willing to switch to SSL if the payback rate is within 1 year and only 10
people out of 100 if the payback rate is within 2 years. From the above simplifying model,
the payback rate is then estimated.
Since current LED technology requires more than 10 lamps to provide the same amount
of lumen output as comparing with an incandescent lamp. It significantly increases the
initial capital cost and the estimated cost of ownership is thus still higher than
incandescent. With projected scenario, LEDs are able to have lower cost than
incandescent starting from 2012. The payback rate for incandescence in 2012 is
approximately 3.8 years. This explains why there is no significant penetration of SSL
even though the cost of ownership of a LED lamp has already surpassed the incandescent
lamp. The penetration of the fluorescent market will start only after year 2015 since the
ownership cost of SSL is still much higher.
Table 5.2 Estimated payback rate for individual sector
5.2 Performance Analysis
As of 2007, the estimated cost of ownership of LEDs is already lower than that of
incandescent lamps. There is no significant replacement of SSL being observed.
Currently, incandescent lamps are mainly used for residential purposes. This is because
initial incandescent lamp costs are low. Although the operation costs of incandescent
lamps are high, residential areas seldom require illumination of more than a couple of
hours per day. The energy saving from residential usage is insignificant. This explains the
high prevalence of incandescent lamps used in homes.
Although the costs of ownership for LEDs are currently lower than that of incandescent
lamps, the penetration rate of LEDs for the residential sector is still slow. This can be
attributed to factors such as consumers being unaware of the potential long term savings
of LEDs due to lower operational costs, lower light output and the poorer color quality of
LEDs compared to incandescent lamps. Even if provided the residential consumers are
aware of the benefits, the majority are willing to pay slightly higher cost for better color
quality lighting for house usage. Moreover, the general public is still skeptical of the
newer LED technology since the cheap and widely available traditional incandescent
lamps have served them faithfully for decades.
From the adoption sensitivity curve, the payback period predicted for incandescent
replacement is also long, leading to poor and slow market acceptance of LED technology.
Therefore, the estimated time frame of full replacement for incandescent will be about 810 years from now. It is approximately around year 2015 onwards.
The costs of ownership of LEDs will be lower than that of fluorescent lamps by 2015.
Fluorescent lamps are mainly used in the commercial sector, due to their longer lifespan
and higher energy efficiencies, leading to huge amounts of long term savings over time.
Companies generally use a lot of lighting over a prolonged period of time. It makes sense
for them to use a lighting scheme that has lower operation costs and which will help them
save in the long run. By 2015, the operation costs of LEDs will be significantly lower
than that of fluorescent lamps. The maintenance costs of fluorescent lamps are higher as
they frequently have to be changed comparing to LED lamps. Since cost reduction is the
usual approach for increased marginal revenue of companies. Their adoption sensitivity is
much higher than those in the residential area. Hence, it is expected that most companies
will switch to using LED lamps as this will help them save a vast amount of money in the
long term. From the cost modeling, the ownership cost of SSL will surpass Fluorescent in
the year 2015. Significant adoption is expected from there onwards.
5.3 Strategy for market penetration of SSL
In the previous section, the cost of ownership modeling and performance of SSL for
general illumination were examined. Armed with this analysis, some strategies which
LEDs companies can follow to allow LEDs to penetrate the market are presented. These
are government initiatives, identification of right market, development of LED products
with attractive design and establishing public trust towards LED technology
Governmentpolicies, initiatives& intervention
To push for SSL, government policies, initiatives and intervention are essential. Private
companies have to consider various governments' initiatives on SSL research and
development and their role in SSL market creation. Moreover, government policies that
regulate the different lighting markets must be considered because they affect continued
consumer interest in these markets, including SSL. The provision of various government
subsidies and incentives may cause an otherwise unprofitable enterprise to be lucrative.
In the midst of the rising fuel prices and the requirement of energy for better living
standards, dependence on oil from potentially unstable parts of the world is arguably one
of the greatest security threats to any nation. Governments worldwide, especially for nonenergy producing countries, are working to decrease dependency on imported oil and
natural gas. Reduced consumption of energy is one of the alternative solutions. The
successful adoption of high efficiency SSL can contribute to significant national energy
saving, a cleaner environment and reduced dependency on foreign sources for daily
running of the economy. Therefore, the government should takes steps to increase
research funding which could encourage the production of more energy-efficient SSL. In
the early phases of development, SSL projects are generally high-risk, long term although
they have potentially significant public benefit. Private companies generally would not be
willing to undertake such risky research. This is when the government should step in.
Upon maturity of a country's research on SSL, private companies will be more willing to
further develop such technology. This is because the time period of duration of bringing
the technology
from
the laboratory to
the marketplace
is shortened
and
commercialization of SSL products is more promising. Hence, government should assist
and subsidies in developing SSL technologies up to such a point whereby the private
sector is willing to further invest and integrate SSL into daily usage and commercialize
such technologies.
In creation of market possibilities for SSL, implementation of certain government policy
and regulation can be done to restrict the usage of non-efficient conventional lighting. It
helps to promote SSL technology and increase the speed of market penetration and
adoption. Consumer awareness and enough education for the benefits of LEDs in the
general lighting market are of the utmost importance. Government publicity of such
advantages will help speed up market penetration.
Therefore, cooperation of governments with private enterprises in pushing for SSL will
result in a win-win situation, for the governments, and for private enterprises as well as
for the consumer at large. For the governments, the nation's vulnerability can be reduced.
For the private sector, successful commercialization of SSL will produce significant
profits. Last but not least, consumers can enjoy a cheaper and innovative form of lighting.
Worldwide, the U.S, Japan, Taiwan, Korea as well as China have government-supported
initiatives for SSL. There are also related activities in Europe. To illustrate the effect of
government policies on research contribution and market creation in SSL, a summary of
various governments' initiative are provide in appendix II.
Identification ofMarket
Over the past 20 years, LEDs have found use in many electronic devices. With the advent
of HB-LEDs that can be used for the full spectrum of colors and which are brighter,
LEDs have been widely used in niche applications such as traffic lighting, cell phones,
flash lights and automotive lighting. LED technology has been doing well in identifying
the right initial market as foundation. The next target for LEDs manufacturers should be
the general illumination market. In order for LEDs to penetrate this market, the
advantages of LEDs should be fully realized. This includes longer reliability, higher
energy savings and ease of replacements. LEDS should first target applications which
would benefit the most from these properties. For example, there will be considerable
ease in maintenance if LEDs were to replace conventional lighting in hard to reach places
such as street lamps or down-light used for corridor illuminations. Successful adoption of
LEDs in such applications will allow LED manufacturers to gain confidence as well as
the funds for future LEDs for penetration into other areas in the future.
Development ofLED Products with Attractive Design
Better design will aid LEDs in replacing incandescent and fluorescent lamps. LEDs can
be integrated and designed for 'plug and play' in conventional incandescent/ fluorescent
lamp sockets. However, integration of LEDs for such use may be counterproductive. For
instance, if we fit many LEDs to form tubes to replace the fluorescent lamps, it would
require numerous LEDs and many advantages of LEDs would not be utilized. Innovative
design could be crucial. Care must be undertaken to balance adaptability of LED products
and advantages of such products. Besides engineering knowledge, other professionals
such as designers should be involved to come up with revolutionary SSL products which
we have never seen before, where such new features and designs could not be realized
from the fragile, bulky conventional light sources. It will be important to form
partnerships to come up with such products. Bulb manufacturers could work with design
companies and fixture companies in designing such attractive products.
Generally, residential consumers assume that their electricity bill from lighting usage is
insignificant. They would not spend time to find which is the most energy efficient
solution available. For them, the key consideration might be only attractive design and
price.
EstablishPublic Trust towards LED Technology
Public trust towards a particular product is essential for the product to successfully take
off. Care must be taken to reduce failure rates. It is important to come up with an industry
standard. Before launching a product, reliability issues must be addressed first. Standards
for SSL are currently not available. Moreover, such standards are difficult to establish as
they are determined by human responses. Measurements of those are difficult to
determine. However, they are crucial if the industry is to develop. LEDs manufacturers
which have experience in testing low-powered LEDs products, they might not have
experience in development of white light since it probably have new set of problem will
need to be addressed and these tests have to be re-established. Failures may occur due to
various and different circumstances. In such cases, it is pertinent for the manufacturers to
obtain feedback from consumers so as to improve on the design. Companies should
prevent in launching immature products because of earning early profits. Reliability issue
could result in unwarranted failures which will reflect badly on the whole industry.
Preventing this from happening will facilitate growth of the whole industry.
Last but not least, reducing costs over a period of time would come with production
experience. Reducing costs will be a major consideration and long term goal in the solid
state industry. For LEDs to be competing with other forms of lighting, innovation from
companies to improve yield as well as productive efficiency is required.
Chapter 6 Conclusion
SSL offers a wide range of benefits. It is more energy saving, is green and more
environmental friendly, has a longer life span and is more robust than conventional
lighting. However, there are a few areas in which SSL lighting has to improve on before
it could replace conventional lighting. The areas to be improved include cost reduction,
light output efficiency and color quality. There has been a spate of ongoing research to
address these issues by both government and private sectors.
General illumination is expected to have a market value of $1 billion in 2010. It is hoped
that SSL will be able to penetrate into this market ultimately by replacing conventional
lighting. This robust growth is expected to be contributed by both government entities
and private enterprises. More niche applications for LEDs are expected to be
commercialized in the next few years. Cost modeling predicts that LEDs will be used for
general illumination in a decade. Strategies to speed up market penetration include cost
reduction and improvements in features. This will ultimately result in a revolution of
lighting devices.
Last but not least, the main aim of successful SSL market penetration is to increase
lighting device efficiency and promote energy conservation. In order to fulfill these, end
users will have to learn to use energy "efficiently". Otherwise, the energy saved by
switching from conventional lighting devices to LEDs will be wasted through the wonton
use of electricity. This will only render research efforts for solid state lighting devices
useless.
Appendix I Simplified ownership cost model
Sample calculation
In year 2007, a LED lamp has the following features,
Flux = 2001m/lamp
Luminous efficacy = 751m/W
Lamp cost = 6 US$/lamp
Lamp cost = Lamp cost/Flux x 1000 = (6/200) x 1000 = 30 US$/klm
Maintenance cost = 1 US$
Input power = Flux/ Luminous efficacy = 200/75 = 2.7 W/lamp
Durability = 20,000 hrs
CRI = 78.5
Using equation 4.1,
Capital cost = 106 x (CB +CM) / (P x 1 x r) = 106 x (6+1)/ (2.7 x 75 x 20,000)
= 1.75 US$/Mlmh
Operation cost = 103 x (CE / rl), where cost of electricity is about 0.07US$/kWh
= 103 x (0.07 / 75) = 0.93 US$/Mlmh
Cost of ownership = Capital cost + Operating cost
= 1.75 + 0.93 = 2.68 US$/Mlmh
implifying assumptions, we project the following scenario,
minous efficacy of LED lamp increase at a rate of 1.1
put power per LED lamp increases at a rate of 1.15
st of LED decreases at a rate of 0.95
nance cost increases at a rate of 1.05
eful life is up to a maximum of 20,000 hours although it could be longer than this value.
ous
y (lm/W)
ility (hr)
m/lamp)
Power
mp)
cost
lm)
cost
amp)
enance
l cost
Mlmh)
ion cost
Mlmh)
ship cost
Mlmh)
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
75
20000
200
80
20000
230
90
50000
270
100
50000
300
110
70000
350
120
70000
400
130
70000
460
150
100000
530
160
100000
610
180
100000
700
200
100000
810
220
100000
930
240
100000
1070
260
100000
1230
2.7
2.8
2.9
3.0
3.2
3.3
3.5
3.6
3.8
4.0
4.2
4.3
4.5
4.8
30.0
24.8
20.5
16.9
14.0
11.5
9.5
7.9
6.5
5.4
4.4
3.7
3.0
2.5
6.0
5.7
5.4
5.1
4.9
4.6
4.4
4.2
4.0
3.8
3.6
3.4
3.2
3.1
1.0
78.5
1.1
79
1.1
79.5
1.2
80
1.2
80.5
1.3
81
1.3
81.5
1.4
82
1.5
82.5
1.6
83
1.6
83.5
1.7
84
1.8
84.5
1.9
85
1.75
1.47
1.23
1.04
0.87
0.74
0.62
0.53
0.45
0.38
0.32
0.28
0.24
0.20
0.93
0.85
0.77
0.70
0.64
0.58
0.53
0.48
0.44
0.40
0.36
0.33
0.30
0.27
2.68
2.32
2.00
1.74
1.51
1.32
1.15
1.00
0.88
0.77
0.68
0.60
0.53
0.47
Table of estimated ownership cost of SSL from year 2007 to 2020
Appendix II Summary of Government initiatives from various countries
USA 17
The USA was one of the first nations to launch national programs to investigate SSL. The
Department of Energy (DOE) and the Next Generation Lighting industry Alliance
(NGLIA) established a partnership that will help support the development and
commercialization of SSL technology. The NGLIA, administered by the National
Electrical Manufactures Association (NEMA), is an alliance of for-profit corporations
formed to accelerate SSL development and commercialization thought governmentindustry partnership. The alliance provides the SSL industry an avenue for
communication and collaboration. Alliance members include 3M, Corning Inc., Cree Inc.,
GELcore LLC, General Electric Company, Lumileds lighting LLC, Osram Opto
Semiconductors and Philips Electronics North America Corporation. With government's
support, the bill designates up to $50 million for NGLIA programme for each of the fiscal
years 2007 through 2009 and extended authorization of the same amount for each of
fiscal years 2010 through 2013.
Japan
One of the first national programs was initiated in Japan. In 1998, the Ministry of
Economy, Trade and Industry (METI) in Japan commissioned the New Energy and
Industrial Technology Development Organization (NEDO) to develop low-energy white
LED light systems'
.
17 http://lighting.sandia.gov/Xlightinginit.htm
1n http://compoundsemiconductor.net/articles/magazine/8/7/3/1
The "light for the
2 1st
Century" project ended in March 200319. Japan's solid-state
lighting project has now entered its second phase. This project has brought together 13
companies and four universities. Research is proceeding in five main areas, namely
substrates, epitaxy, devices, lamps and fixtures. Other investigations include general
illumination considerations suchs as how objects appear under lighting, and the optimum
arrangement of devices and their effects on perception. A CRI value of more than 90 is
being sought for an LED fixture with a luminous efficacy of 801m/W. This is comparable
to the output of a fluorescent bulb.
20
China 21
The Chinese government is funding a national program to position the country as a leader
in SSL. As the SSL industry evolves, it becomes increasingly clear that China will
become both an enormous consumer for lighting products and an engine for growth and
innovation in SSL. The Chinese government has launched a national SSL program,
targeting huge energy savings from a large-scale conversion to LED lighting, as well as
reduced environmental pollution. The China National SSL program kicked off in June
2004 when the Ministry of Science and Technology pulled together the activites of a
number of different regional development groups. The program has already received 140
million RMB from the central government, and 15 research institutions and more than 50
enterprises. The country already has 4 national SSL industrial bases, in the cities of
Dalian, Shanghai, Nanchang and Xiamen. A fifth base is under development in Shenzhen.
Taiwan
Ten members of Taiwan's LED lighting industry have formed a consortium to accelerate
the development of white LEDs. The Next Generation Lighting Plan aims to improve the
19 http://compoundsemiconductor.net/articles/magazine/8/7/3/1
20 http://www.ledsmagazine.com/news/1/12/14/1
21 http://ledsmagazine.com/features/2/2/5/1
performance of white LEDs produced by combining UV LED chips with RGB phosphors.
The consortium includes LED chip makers Epistar, Tyntek and Opto Tech. The other six
members are LED packaging companies, namely LEDbright, Everlight, Ledtech, Uni,
Paralight and Kingbright 22.
Funding is provided by the Economic Affairs department of the Taiwanese government
and by the participants, amounts to NT$380 million. Intellectual property developed
during the program will be shared by the participating companies, who will all look to
commence mass production of white LEDs at the appropriate time.
South Korea23
With no domestic oil supply, the Korean government is very keen on LED technology
and is pouring hundreds of millions of dollars into LED development. The main research
is carried out by Korea photonics technology institute (KOPTI). Korea's LED
infrastructure is now benefiting from the launch of a national program for the LED
industry, in which Samsung and LG are big players internationally. Besides, through the
LED valley project, it is predicted that penetrating of external automotive LED lighting
will occur in 2008.
Europe
The European Union is also investing in programs that either directly or indirectly
support SSL. In March 2006, DTI Global Watching Mission led by Photonics Cluster
(UK) visited the U.S to better understand the current technologies, applications and
strategies for the adoption of SSL.
22
http://www.ledsmagazine.connews/1/2/l/1
23 http://ledsmagazine.com/features/2/4/2/1