Promises and Challenges of LED Technology for Lighting ... · implementing LEDs into applications that increase the LED junction temperature. Performance of commercial LEDs vary significantly

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

© 2007 Rensselaer Polytechnic Institute. All rights reserved.

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.


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


LRC MissionAdvancing the effective use of light and creating a positive legacy for society and the environment


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)


Collaboration – LRC Partners


The objective, third-party

source of reliable lighting

information.

Objectivity

NATIONAL LIGHTING PRODUCT INFORMATION PROGRAM


EducationGraduate Education – M.S. in Arch Science – 1 yr

• Concentration in Lighting

– M.S. Lighting – 2 yr

– Ph.D. Lighting


International OutreachDenmarkDenmarkFinlandFinlandNorwayNorwaySwedenSweden

IndiaIndiaPhilippinesPhilippines

CanadaCanada

ItalyItalyNetherlandsNetherlands

JapanJapan

EnglandEngland

Latin AmericaLatin America(CIELA)(CIELA)

S. KoreaS. Korea

ChinaChina

GermanyGermany

USAUSA

SingaporeSingapore


Introduction to LightingIntroduction to Lighting


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


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


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


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


LED PromisesLED Promises


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


Other PromisesRugged and durable

Unique lighting solutions – intensity and color modulation

Smaller unique lighting fixtures

Environmentally friendly

Introduction to LED


JunctionLight

P N-+

- --++

+

+ ---

-Electrons

--

What is a LED?


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


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


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


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


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


Industry TrendGrowing number of LEDs and LED fixtures


Early LED Applications


LED Applications: Colored Light


LED Applications: White Light


LED Applications: TransportationBoeing 787 2008 Lexus LS 600h L

First LED headlamp


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.


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.


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


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


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


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


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

)


Are LEDs suitable for directional lighting?


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


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


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)


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


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


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

)


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.


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.


Challenges:Lack of Industry Standards


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.


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


ASSIST Program Sponsors


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.


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


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.


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


LRC’s SSL Web Site

www.lrc.rpi.edu/programs/solidstate

Documents

Promises and Challenges of LED Technology for Lighting ... · implementing LEDs into applications that increase the LED junction temperature. Performance of commercial LEDs vary significantly