Dr. N. Narendran
Lighting Research CenterRensselaer Polytechnic Institute
Troy, New York, USA
http://www.lrc.rpi.edu/programs/solidstate
Promises and Challenges of LED Promises and Challenges of LED Technology for Lighting ApplicationsTechnology for Lighting Applications
New Delhi, IndiaJune 8th 2007
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AcknowledgmentsI wish to thank
ISLE and USAID
LRC Faculty, Staff, and Students– Special thanks to: Yimin Gu, Lalith Jayasinghe, Jean Paul
Freyssinier, Jennifer Taylor, Martin Overington, Tianming Dong, and Yiting Zhu
All the LRC project sponsors who provided financial support for the studies described here.
© 2007 Rensselaer Polytechnic Institute. All rights reserved.
Rensselaer’s Lighting Research CenterRensselaer is the oldest engineering university in the U.S.
LRC is the largest university-based center for lighting research and education.
Started in 1988
RPI/LRCRPI/LRCTroy, NYTroy, NY
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LRC MissionAdvancing the effective use of light and creating a positive legacy for society and the environment
© 2007 Rensselaer Polytechnic Institute. All rights reserved.
LRC Staff and Facilities30 Full-time faculty and staff– Physics/Engineering
– Biophysics
– Psychology/Physiology
– Architecture/Lighting Design
Research– Technology
– Human factors
– Design
30,000 sq. ft. of research space with well-equipped laboratories. NVLAP accredited testing facility (NIST Traceable)
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The objective, third-party
source of reliable lighting
information.
Objectivity
NATIONAL LIGHTING PRODUCT INFORMATION PROGRAM
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EducationGraduate Education – M.S. in Arch Science – 1 yr
• Concentration in Lighting
– M.S. Lighting – 2 yr
– Ph.D. Lighting
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International OutreachDenmarkDenmarkFinlandFinlandNorwayNorwaySwedenSweden
IndiaIndiaPhilippinesPhilippines
CanadaCanada
ItalyItalyNetherlandsNetherlands
JapanJapan
EnglandEngland
Latin AmericaLatin America(CIELA)(CIELA)
S. KoreaS. Korea
ChinaChina
GermanyGermany
USAUSA
SingaporeSingapore
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Lighting HistoryOver the past 100 years, incandescent and gas discharge technologies have provided many light fixtures for a variety of lighting applications.
www.sportsvenue-technology.com/contractors/flood/abacus/abacus2.htmlimages.google.com/images?q=hotel%20lighting&hl=en&lr=&ie=UTF-
8&sa=N&tab=wi
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SolidSolid--State Light SourcesState Light Sources
Light Emitting Polymer (LEP)Light Emitting Polymer (LEP)
Light Emitting Diode (LED)Light Emitting Diode (LED)
UniversalUniversal--displaydisplay
Evolving New Technology
Cree XLamp® LED
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Lighting22%
Other78%
.
Motivation for Solid-state LightingAbout 22% of the total energy use in the U.S.
Demand for energy keeps increasing
Industrial14%
Outdoor Stationary
8%
Commercial51%
Residential27%
Source: U.S. DOE Website
Source: U.S. DOE
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Worldwide ProgramsMany countries around the world have recognized the possibilities for solid-state lighting and have initiated government-supported national activities: – U.S.A.
– Japan
– Taiwan
– Korea
– China
– Europe
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Promise: by 2012
15 lm/W
90 lm/W
120 lm/W
150 lm/WEnergy savings
1000 hrs
20,000 hrs30,000 hrs
100,000 hrsLower maintenance cost
© 2007 Rensselaer Polytechnic Institute. All rights reserved.
Other PromisesRugged and durable
Unique lighting solutions – intensity and color modulation
Smaller unique lighting fixtures
Environmentally friendly
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JunctionLight
P N-+
- --++
+
+ ---
-Electrons
--
What is a LED?
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LED Spectral Outputs
0.0
0.2
0.4
0.6
0.8
1.0
400 450 500 550 600 650 700 750
Wavelength (nm)
450 nm 650 nm530 nm 590 nm
LED Spectrum
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White LED PackageCurrent practice: Blue/UV LED is surrounded by phosphor
To achieve higher light output and efficacy with white LEDs, improvements are needed at several stages: – internal quantum efficiency
– extraction efficiency
– phosphor-conversion efficiency
DieEpoxy
& phosphor
Reflector
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High-power LED
Higher flux per device
Higher efficiency
Better color properties for white LEDs– Good color rendering
– Much lower color variationbetween lamps
– More stable color over time
Longer lifeDevices from: Lumileds, OSRAM Opto, Nichia, CREE, Lamina Ceramic, Seoul Semiconductor
Lamina
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Ballast (Driver)
Heat Sink
Optics (Lens)
LED Array
Optics (Diffuser)
Electrical Grid
Fixture Housing
Controls
Circuit Board
LED Lighting SystemSystem components and optimization
– Electrical
– Optical
– Mechanical
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AC LED
New to LED family– AC operation (120V/240V)
– No need for drivers
Presently less efficient than a DC LED, but with further improvements comparable efficiencies can be achieved.
http://seoulsemicon.co.kr/_homepage
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Industry TrendGrowing number of LEDs and LED fixtures
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LED Applications: TransportationBoeing 787 2008 Lexus LS 600h L
First LED headlamp
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Application TrendTo date, colored light applications are the most popular.– Compared to traditional light sources, LEDs offer
greater benefits:• Less energy
• Longer life
• More control options
• Shallow-profile fixtures
White light applications are just starting.
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Going ForwardLED – Will soon be one of the light source choices for illumination applications.– The potential for reduced energy use and
lower maintenance costs are two key attributes of this rapidly evolving technology that have generated so much interest for its use.
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Evolving LED ApplicationsIllumination applications targeted by the LED community in the near-term are:– Indoor – Under-cabinet lighting
– Indoor – Directional lighting (downlights)
– Outdoor – Street and parking lot lighting
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Directional LightingIncreasing interest for using LEDs in directional lighting applications.
Presently, there are many light sources available to cater to these applications.
IncandescentHalogen CFL HID LED
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For Energy SavingsIt is incorrect to think that high luminous efficacy sources will save more energy in lighting applications.
Some light sources have high luminous efficacy, but when used in lighting fixtures, the total fixture efficacy can be very low.
Therefore, one must consider:– Complete system efficacy
– Application efficacy• Delivered light to the application
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CFL Downlight FixturesAlthough CFL source efficacy is around 70 lm/W:– The total system efficacy for
downlights are in the range of 30% to 50%
– This means as a system, the efficacy could be as low as 21 lm/W.
CFL
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Total System Efficacy for Different Technologies
Total fixture efficacy ~ 7 to 39 lm/W
LEDs are becoming competitiveDownlight Fixtures
39
24
711 14 15
25
13
23
0
10
20
30
40
50
CFL 1CFL 2IN
C 1IN
C 2IN
C 3LED1LED 2LED 3LED 4
Fixt
ure
Effic
acy
(lm/W
)
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Are LEDs suitable for directional lighting?
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Example: DownlightingGenerally, downlight fixtures used in residential, office, and hospitality applications produce around 600 lumens per fixture.
In 2007, the power demanded by some commercial LED fixtures is approaching that of CFL downlight fixtures.
– In the future, LED fixtures could become more energy efficient than CFL fixtures.
– However, there are many commercial LED fixtures with very poor performance.
Watts to yield 600 lm per fixture
0
20
40
60
80
100
0 10 20 30 40 50Fixture efficacy (lm/W)
Fixt
ure
pow
er (W
)
CFLs
INC
LEDs
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Initial CostAt the present time, most LED lighting fixtures have a higher initial purchase cost than incandescent or fluorescent fixtures. – Approximately 6 to 10+ times higher
Downlights: – Incandescent 75W ~$50
– CFL ~$90 to $140
– LEDs PC ~$300 to $500
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What is the lifecycle cost of an LED system?Why lifecycle cost?– Consumers are becoming more aware of costs beyond initial
purchasing cost.
– A meaningful way to compare systems with different • Initial and installation costs• Operation costs (energy, relamping, other maintenance)• Operational lifetimes
As an example, a 16 ft. by 16 ft. area was analyzed with different downlight fixtures (all systems produced about 180 lx on the task)
• A residential setting (with 3 to 4 hrs use per day)• A commercial setting (with 10 to 12 hrs use per day)
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Lifecycle CostAt the present time, in residential lighting LED lighting costs more than incandescent or fluorescent lighting.
In hospitality applications, the cost of using LED systems is approaching the cost of using traditional lighting systems.
– The following cost estimates are based on the assumption that LED systems would last 50,000 hrs or longer.
Residential Application
$0$500
$1,000$1,500$2,000$2,500$3,000$3,500
Inc 1
Inc 2
Inc 3
CFL 1
CFL 2
LED 1
LED 2
LED 3
Tota
l Cos
t for
10y
rs
Hospitality Application
$0$1,000$2,000$3,000$4,000$5,000$6,000$7,000
Inc 1
Inc 2
Inc 3
CFL 1
CFL 2
LED 1
LED 2
LED 3
Tota
l Cos
t for
20y
rs
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Application ConsiderationsDirectional lighting products experience a wide range of environmental conditions.– Ventilated– Semi-ventilated– Fully enclosed
Heat at the LED junction increases as the ventilation around the LED is reduced.
Presently, it is very difficult to create stable white light with mixed-color white LED systems.– Not suited for white light applications– Color would shift over time and ambient temperature
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Impact of Heat on LEDsHeat negatively affects the performance of LEDs– Light output
– Color
– Life (~ half the life for every 10°C)
1 Watt White LEDs
60%70%80%
90%100%110%
40 60 80 100 120Tj
Rel
ativ
e lig
ht o
utpu
t
LED A
LED B
LED C
R2 = 0.96
010000
2000030000
4000050000
35 40 45 50 55 60T-point Temperature (deg C)
Life
(hrs
)
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Life of LEDs and LED SystemsSince heat shortens LED life (roughly half the life for every 10°C increase at the junction), system manufacturers have to provide sufficient heat sinking to ensure longer life.Additionally, installers have to make sure that they are not implementing LEDs into applications that increase the LED junction temperature.Performance of commercial LEDs vary significantly.Some good white LEDs have a lifetime in the range of 100,000 hrsplus, but there are many other products that have life time as short as few thousand hours.Presently, there are many commercial systems that may not have long life – Usually in the range of 10,000 hrs or less
Buyers have to request life data from fixture manufacturers per ASSISTRecommends.
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Summary – LEDs in directional lighting
Some of the presently available LEDs can cater to directional lighting applications.– LEDs perform much better in open-air operation
• Track lights, surface mount lights, etc.
– LEDs will have a much shorter life in applications where the ventilation is poor and heat is trapped.
Presently, LED systems cost higher than traditional lighting systems.– They are becoming cost competitive in some commercial
applications.– With rapidly improving performance and decreasing cost of LEDs,
these systems will become more cost effective in the next few years.
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Why Standard Definitions and Metrics?Lack of standard definitions and metrics for LED technology has led to confusion among lighting professionals.– Some of the lighting specifiers are already frustrated with
LED technology.
Many definitions and metrics used in the traditional lighting industry are not applicable to LED technology.
For LED technology to be widely used in general lighting applications, standard definitions and metrics are essential.
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Industry ActivitiesMany organizations are in the process of implementing programs to enable standards activities
ASSIST is conducting research to develop information that can be useful for metrics and setting standards.
ASSIST(Alliance for Solid-State Illumination Systems and
Technologies)
Established: In 2002
Goal: To support the development and widespread application of energy-efficient solid-
state lighting technologies
Activities: Industry collaboration, research and demonstration, education
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ASSIST RecommendsASSIST recommends is a program of the Alliance for Solid-State Illumination Systems and Technologies (ASSIST).
When standard definitions and metrics for LED technology are notavailable, ASSIST develops and publishes recommendations.– The recommendations are developed through research conducted on
behalf of ASSIST by the LRC.
ASSIST Recommends helps manufacturers present meaningful information to end users in a consistent manner.
ASSIST also publishes application guidelines to help end-users select and apply LED technology successfully.
© 2007 Rensselaer Polytechnic Institute. All rights reserved.
ASSIST RecommendsThe first ASSIST Recommends, “LED Life for General Lighting” was released in 2004.
– Life definition: 70% lumen maintenance (50% for indicators or decoration)
– Life reported by both LEDand fixture manufacturers
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Current StatusSome of the LED manufacturers are already collecting and reporting data per ASSIST Recommends.
Several organizations including standards-setting organizations have referenced ASSIST Recommends LED Life.
© 2007 Rensselaer Polytechnic Institute. All rights reserved.
New
New ASSIST Recommends Publications
Under-cabinet Lighting
Directional lighting
Three parts– General guide to applications– Guide to selecting LED fixtures– Testing and evaluation recommendations
Audiences– Guides – Homeowners, general contractors– Testing and evaluation – Manufacturers, standards-
setting bodies, state and federal agencies, public benefit program administrators, independent test labs