Integrating LEDs into your Design - Efficiency Vermont · 2020. 1. 31. · Gallium 69.723 32 Ge...

©2010 LED Transformations, LLC

Integrating LEDs into your Design

BETTER BUILDINGS

BY DESIGNCONFERENCE 2010

February 10, 2010

Dr. John W. Curran, President, LED Transformations, LLC

Copyright Materials

This presentation is protected by US and International copyright laws. Reproduction,

distribution, display and use of the presentation without written permission of

LED Transformations, LLC is prohibited.

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Thank you!

Efficiency Vermont is a Registered Provider with TheAmerican Institute of Architects Continuing EducationSystems. Credit earned on completion of this programwill be reported to CES Records for AIA members.Certificates of Completion for non-AIA members areavailable on request.

This program is registered with the AIA/CES for continuing professionaleducation. As such, it does not include content that may be deemed orconstrued to be an approval or endorsement by the AIA of any materialof construction or any method or manner of handling, using,distributing, or dealing in any material or product. Questions related tospecific materials, methods, and services will be addressed at theconclusion of this presentation.

Better Buildings By Design 2010


Learning Objectives

Integrating LEDs into your Design

0 - 4

At the end of this program, participants will be able to:

• Evaluate when LED's are appropriate for your design choice.

• Examine the facts on product evaluation and selection

• Explain the advantages and disadvantages among various products

• Understand key measurement and analysis tools including modeling, light-loss factors and savings potential


Course Outline

1. Introduction: What Led to LEDsa) History b) Terminology

2. Physics of LEDs: The Science Behind the Technology3. The LED “System”: A Series of Trade-offs

a) Electronics Considerationsb) Thermal Considerations c) Photometric Considerations d) Lifetime Considerations

4. Standards for SSL: A Whole New Set of Rules5. Recommendations: How to Survive in the Solid State

Lighting Future

©2010 LED Transformations, LLC 0 - 5

Introduction

What Led to LEDs

Introduction

LEDs are like no other conventional lighting source

+ Longest life of any lighting sources

+ High energy efficiency and improving yearly

+ Small size and instant on allows new

applications

+ Integrates will with other semiconductor

electronic elements

- Thermal management requirements

- Cost

- New world for architects, lighting designers and manufacturers

1 - 7©2010 LED Transformations, LLC

HistoryBackground – LEDs represent a “revolution” in lighting

• Small Size

• High Efficiency

• Many Colors

• No Mercury Hg

• Long Lifetimes

4.49mm

=

Source US Dept of Energy 10/07


Introduction

HistoryBackground – So why are LEDs becoming so popular?

Incandescent/Halide (26% / 21%)

Compact Fluorescent (21% / 19%)

HID (7% / 5%)

Linear Fluorescent (42% / 43%)

LED (2% / 11%)

Other (2% / 1%)

2007

2012

Light Sources (2007 / 2012)

Source: Strategies in Light 2008


Introduction

HistoryBackground – Market Sizes

Introduction


Ben Franklin BridgePhiladelphia Boeing 787

Dreamliner

Los Angeles Airport

HistoryBackground – Color changing applications

Introduction


Hard Rock HotelLas Vegas

Full Moon TowerTainjan, China

“Water Cube”Beijing China

Five BoatsDuisburg, Germany

HistoryBackground – Architectural applications

Introduction


Toronto, CanadaSource LED Magazine

Ann Arbor, MI

Raleigh, NC

HistoryBackground – Street/Area lighting applications

Source BetaLED

Raleigh, NC

Source US DOE

Introduction


Incandescent 5,135 W

LED 948W

Source CreeFriendly’s Restaurant, Westfield MA

HistoryBackground – Retail / Food Service applications

Introduction


HistorySolid State Lighting is not the first lighting revolution to confuse people


Introduction

HistorySSL Light Sources - Electroluminescent Lighting in 1959

16

1962 First LED (Holonyak at GE) 0.001 lumens

1960’s Red LEDs (HP & Monsanto) 0.01 lumens

1970’s First consumer products - Watches, calculators

1980’s Green LEDs 0.1 lumens

1990’s Blue LEDs (Nakamura at Nichia) 1 lumen

2000’s High flux packages 100+ lumens


Introduction

HistorySome LED Milestones

Introduction


TerminologyColor—Eye Response: Radiometric to Luminous Flux

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

400 450 500 550 600 650 700

Wavelength (nm)

Photopic Eye Response

Introduction

X, Y and Z are the spectral responsecurves for the three different conereceptors in the eye. If the eyeresponse to a color stimulus is givenby X, Y and Z, we can define a colorcoordinate system as the relativestimulus given by the following equations:

_______ _______

_______


x =

z =

y = X + Y + Z X + Y + Z

X + Y + Z

X Y

ZWith X + Y + Z = 1 by definition,

only two coordinates arenecessary to define a color

Spectral Response

CIE Chart (1931)

TerminologyColor—Definitions

Introduction


TerminologyCorrelated Color Temperature

PlankianBlackbody

Curve

CCT Light Source1500 K Candlelight

2680 K 40 W incandescent lamp

3000 K 200 W incandescent lamp

3200 K Sunrise/sunset

3400 K Tungsten lamp

3400 K 1 hour from dusk/dawn

5000-4500 K Xenon lamp/light arc

5500 K Sunny daylight around noon

5500-5600 K Electronic photo flash

6500-7500 K Overcast sky

9000-12000 K Blue sky

Introduction


Figure courtesy Ian Ferguson, Georgia Tech

Figure from “Light Emitting Diodes, 2nd edby E. Fred Schubert

Blue, green and white LEDsgenerally have higher forwardvoltages than do amber, orangeand red

TerminologyForward Voltage

Forward Voltage Vf is roughly equal to the

bandgap energy of the LED semiconductor

divided by the elementary charge

Vf = Eg / q

where q =1.6 x 10-19 coulombs

Physics of LEDs

The Science Behind the Technology

Physics of LEDs

A diode is a component that restricts the directional flow of charge

carriers. Essentially, a diode allows an electric current to flow in one

direction, but blocks it in the opposite direction. Circuits that require

current flow in only one direction typically include one or more

diodes in the circuit design.


Anode Cathode

LEDSymbol

Diode Rectifier Bridge

- 1. 2

- 1

- 0 . 8

- 0 . 6

- 0 . 4

- 0 . 2

0

0 . 2

0 . 4

0 . 6

0 . 8

1

1. 2

0 5 0 10 0 15 0 2 0 0 2 5 0 3 0 0 3 5 0

- 1. 2

- 1

- 0 . 8

- 0 . 6

- 0 . 4

- 0 . 2

0

0 . 2

0 . 4

0 . 6

0 . 8

1

1. 2

0 5 0 10 0 15 0 2 0 0 2 5 0 3 0 0 3 5 0

What is a diode?

Physics of LEDs


Typical constructionfor a 5mm LED

Typical construction for a

High Flux LED

Typical Flux = 3 lm Typical Flux > 75 lm

Number of LEDs to equal theoutput of a 60W incandescent

light bulb > 250

Number of LEDs to equal theoutput of a 60W incandescent

light bulb < 12

LED Chip

Gold Wire

Cathode

Anode

Reflector CupEpoxy Lens

SiliconSubmount

Cathode

Outer PackageGold Wire

LED Chip

Lens

Heatsink

The heatsink is what allows the high flux LED togenerate muchmore light

Types of LEDs

Physics of LEDs


Types of LEDs

Discrete LEDs come in many shapes and sizes

Physics of LEDs


Types of LEDs

Likewise, high flux LEDs also come in many forms


Group IIIA Group IVA Group VA

5

BBoron

10.811

6

CCarbon

12.0107

7

NNitrogen

14.006

13

AlAluminum

126.981

14

SiSilicon

28.0955

15

PPhosphorus

30.973

31

GaGallium

69.723

32

GeGermanium

72.61

33

AsArsenic

74.921

49

InIndium

114.818

50

SnTin

118.710

51

SbAntimony

121.760

Base Elements

P-Type Dopants

N-Type Dopants

AlInGaP

AlInGaN

Physics of LEDs

LED chemical composition

Physics of LEDs


Source: Molecular Expressions

Semiconductor “doping”


Physics of LEDs

5e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

4e

5e

3e

4e

4e

4e

4e

4e

4e

4e

3e

Base

Structure

P Doped

Structure

N Doped

Structure

free

electrons

free

holes

2 - 28

Physics of LEDs

For metals Eg is small; for insulators Eg is very largeMaterials between these two extremes are knownas semiconductors

When electrons and holes combine, the resultingphoton has a wavelength related to the bandgap

energy given by λ = 1239 /


Ev - Top of Valence Band

Ec - Bottom of Conduction Band

Eg

Electron Hole

Eg

Material SymbolBand gap (eV)

@ 300K

Silicon Si 1.11

Germanium Ge 0.67

Silicon carbide SiC 2.86

Aluminum phosphide AlP 2.45

Aluminium arsenide AlAs 2.16

Aluminium antimonide AlSb 1.6

Aluminium nitride AlN 6.3

Diamond C 5.5

Gallium(III) phosphide GaP 2.26

Gallium(III) arsenide GaAs 1.43

Gallium(III) nitride GaN 3.4

Gallium antimonide GaSb 0.7

Indium(III) phosphide InP 1.35

Indium(III) arsenide InAs 0.36

Zinc oxide ZnO 3.37

Zinc sulfide ZnS 3.6

Zinc selenide ZnSe 2.7

Zinc telluride ZnTe 2.25

Cadmium sulfide CdS 2.42

Cadmium selenide CdSe 1.73

Cadmium telluride CdTe 1.49

Lead(II) sulfide PbS 0.37

Lead(II) selenide PbSe 0.27

Lead(II) telluride PbTe 0.29

Conductivity of various materials

30

N Type P Type

Free electrons

Donor atoms

Acceptor atoms

Free holes N Type P Type

Depletion Zone

Junction

{

Anode Cathode

It takes a minimum voltage applied to the diode to get electrons and holes to flow across this depletion zone


Physics of LEDs

How do you make a diode?

Physics of LEDs

• Depletion zone creates a barrier which limits flow of carriers (electrons and holes)

• Applying a forward voltage V lowers that barrier and allows carriers to flow across the junction


N Type P TypeN Type P Type

Forward voltage applied

Electron flow

Hole flow

qV

Current flow and forward voltage

32

electron

hole

photon


Physics of LEDs

Radiative recombination(Photon generation)

33©2010 LED Transformations, LLC 2 - 33

Physics of LEDs

Nonradiative recombination(Phonon or heat generation)

Physics of LEDs

Due to the high Index of Refraction of the semiconductor

(ns) as compared to the epoxy dome material (ne),

by Snell’s law, photons exiting the active layer at

angles greater than the escape cone angle θc

will be reflected back into the semiconductor

and will not exit the device.

Some device manufacturers cut the sides of the chips to provide better exit angles and extract more light while others rough the surfaces of the chips

to create optical interfaces which can improve the overall

light extraction. A third approach is to use what are known

as photonic crystals to reduce certain propagation modes

(reflected) and increase others (exiting).


ns

ne

Active layer

Absorbing substrate

θc

Source: Lumileds

Light extraction

Physics of LEDs


Courtesy Ron BonnePhilips Lumileds

LED wafer fabrication facility

Physics of LEDs

If the semiconductor being grown has

a different crystal structure and lattice

constant from the substrate, defects

form at or near the interface of the

two semiconductors. These defects

result in a reduction of optical output.

A mismatch of greater than 0.6% has

been shown to reduce light output in

AlInGaP LEDs by over 92%. The high

mismatch of InGaN crystal with the

saphire substrate is believed to limit

device efficiency for blue/green/white LEDs.


LatticeConstant A1

LatticeConstant A0

Dangling Bond Dislocation

Lattice matching

Physics of LEDs

• Some defects are introduced intentionally, for example the dopants used to create LED dies

• Other, unintended defects can be formed in the semi-conductor in a number of ways– Foreign atoms (contamination)

– Interstitials (atoms at undesirable points in the lattice)

– Vacancies (missing atoms in the lattice)

– Antisites (atoms switched in the lattice)

– Dislocations (an atom in a wrong position in the lattice)

• Defects have energy level structures different from doping atoms and may form one or several energy levels within the forbidden gap

• These additional energy levels increase the amount of non-radiative recombinations, thus decreasing the device photometric output


Lattice defects

The LED “System”

A System of Trade-offs

The LED System

4 - 39

LEDs are only part of the Solid-State Lighting System

• LEDs need several components to function.

– LED Chip/Device/Package

– Driver

– Optics

– Heatsink

=+ ++


http://www.core77.com/blog/object_culture/philips_leds_the_way_12817.asp

Some relationships are obvious

LED Optics

Driver LED

LED Thermal Management

The LED System

Design Trade-off Relationships


Some relationships are not

Optics Thermal Management

Cost Efficacy (Efficiency)

LED Luminaire Housing

The LED System

Design Trade-off Relationships


©2010 LED Transformations, LLC 42

Controller

Driver

LED source

Optics

Thermal

management

The LED System

LED System Elements

The LED System

4 - 43

LED Drivers

• LED Drivers convert the power source to a voltage and current suitable for operation of the LED chips– LEDs are non-linear devices (Vf vs. If) and

typically require constant current sources– Drivers usually incorporate circuitry to

produce PF’s close to 1 (purely resistive incandescent bulbs have PF=1)

• Component makeup determines its life– Electrolytic Capacitors – aging and drying

out of electrolytic– Transistors – stressed by heat and vibration– Other components – exposure to heat,

moisture, environment

• They come in a variety of shapes and sizes


The LED System

4 - 44

Each application requires it’s own driver.

• The many types of drivers include:

– AC/DC: AC input is converted to the DC input for an LED

– DC/DC: Voltage is changed or current is regulated

• The simplest driver is a Resistor

• More advanced drivers incorporate more electronics

– Voltage and/or Current regulation

• Transformers

• High speed electronic switches (Transistors)

• Feedback

• Switch Mode Driver: A power supply that incorporates power handling electronic components that are continuously switching on and off with high frequency to

provide the transfer of electric energy

– Advantage: Very efficient; Good current regulation

– Disadvantage: Cost; High frequency noise


©2010 4 - 45

Typical efficiencies range from 75% to 90% for SMPS

Losses due to switching, resistances, transformers, etc.

Poor power factor results in excess energy use

WattsVolts x Amperes

Driver should not draw power if load is not on (Energy Star requirement)

Harmonic Distortion‏

o Due to non-linear loadsproduced by LEDs


The LED System

PF = ≤ 1

Pure AC Waveform

Distorted AC Waveform

Driver Efficiency

©2010

The LED System


Drivers can incorporate controls

• A single driver can control RGB LEDs that can vary color.

• Dimming an LED can be done in a couple ways:

– Varying voltage and current can be used tovary the light output, however it can also varyother characteristics such as color and maynot achieve full dimming from 0-100%.

– A technique called Pulse Width Modulation (PWM)allows LEDs to dim in alinear fashion from 0-100%.

• Self regulation can also be done using feedback from thermal or optical sensors.

• Output compensation is used to maintain a certain light output when conditions in the system or environment change.

0.000 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.010

0

1

2

3

4

5

6

0.000 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.010

0

1

2

3

4

5

6

PC White• Current reduction approach produces more yellow characteristics as

dimming is increased

• PWM approach produces more blue characteristics as dimming is increased


The LED System

Controllers—Color Shift with Dimming

Source: Marc Dybal et al.,Fifth International

Conference on Solid State Lighting, SPIE, 2005

RGB White• Current reduction approach shifts color characteristics more toward green

as amount of dimming is increased

• PWM approach shifts color characteristics more toward the red-amber as amount of dimming is increased


The LED System

Source: Marc Dybal et al.,Fifth International

Conference on Solid State Lighting, SPIE, 2005

Controllers—Color Shift with Dimming

• Diffused optics scatter light in many directions

• Creates a more uniform

appearance for the light

• Decreases efficacy of sourceOptic Material

Incre

asin

g D

iffu

sio

n

Incre

asin

g E

ffic

acy

The trade-off

The LED System


Optics: Diffusion to Avoid Hot Spots


The LED System


Thermal ConsiderationsWhy is heat such an issue with LEDs?

Heat Loss (%)

Radiation Convection Conduction

Incandescent 15 90 5 5

Fluorescent 100 40 40 20

HID 150 90 5 5

LED 100 5 5 90

Efficacy

(lm/W)Source

Radiated Heat Conducted Heat

Ceiling Tile

Incandescent Fixture LED Fixture

The LED System

4 - 51

Thermal Considerations

Active cooling – More efficient

Passive cooling – More reliable

Thermoelectric Coolers (Peltier)Fans


Piezo fans

HeatsinkHeatpipesMetalcore

PCBs


The LED System


Sintered metal or V-grooves

HOT ENDHeat in

COLD ENDHeat out

Hot water vapor

Cold water

Thermal ConsiderationsHow a heat pipe works


The LED System


Flux versus temperature

0%

20%

40%

60%

80%

100%

120%

140%

160%

180%

200%

-20 0 20 40 60 80 100 120

Temperature (ºC)

Re

l. F

lux

White

Blue

Green

Yellow

Red

250C

Thermal ConsiderationsThermal effect on light output


The LED System


• Ambient temperature greater than 25oC will result in lower light output– Some nighttime outdoor and refrigerated indoor

applications may benefit

• Almost all applications will have a duty cycle greater than the 2.5% that LED manufacturers specify for their light output testing– Higher junction temperature

• LED light output is not linear as a function of current

• Drivers lower LED system efficiency– Most drivers have efficiencies <90%

1.5

84%

350 mamp

700 mamp

Thermal ConsiderationsCurrent and thermal effects


The LED System

Heat flow can be modeled by analogy to an electrical circuit where:Q (heat flow) is represented by current and indicates the power dissipatedT (temperatures) are represented by voltagesRθ (thermal resistances) are represented by resistors andHeat sources are represented by constant current sources

In the simple model below, a semiconductor device is attached directly to a heat sink which is exposed to the ambient air. Semiconductor manufacturers supply the thermal resistance value Rθ j-c between the junction and the case of the device. Similarly heat sink manufacturers supply the thermal resistance of their devices. The thermal resistance of the interface between the semiconductor case and the heat sink is a function of how the device is attached.

For this case the total power dissipated, Q is related by

(Tj – Ta) = Q x (Rθ j-c + Rθ c-h + Rθ h-a )

where Tj is the junction temperature of the semiconductor device and Ta is the ambient air temperature. For reference Tc is the case temperature of the semiconductor device and Th is the heat sink temperature.


Tj Tc Th TaRθ j-c Rθ c-h Rθ h-a

Q

SemiconductorDevice

Heat Sink

Thermal ConsiderationsThermal Resistance (Rθ)


The LED System

• Effectiveness of connections– Thermal pads

– Voids in thermal epoxy

• Orientation of luminaire– Direction of air flow

• End user application– Ambient conditions

– Installation conditions

• Thermal Resistance changes over time– Dirt buildup

– Chemical surface changes


LED Chips

Rθ j-sp

Rθ j-sp

Rθ j-sp

Rθ j-sp

Rθ j-sp

Rθ j-spRθ sp-h Rθ h-a

Tj

Tj

Tj

Tj

Tj

Tj

Th TaTsp

SolderPoint

HeatSink

AmbientAir

Thermal ConsiderationsThings to keep in mind concerning thermal paths

© 2010 LED Transformations, LLC 5 - 57

The LED System

100% effective 85% effective

70% effective60% effective

Thermal ConsiderationsMounting orientation matters

Thermal resistance of a heat

sink is a function of the volume

as well as the flow rate of the air

surrounding the heat sink.

Airflow depends or heat sink

orientation as shown in the

diagrams at left.


The LED System

Wal-Mart has spent about $30 million to develop the refrigerator LED lighting system with General Electric and Royal Philips Electronics


Thermal ConsiderationsLED performance in cold temperatures

Fluorescent Temperature

Dependence

© 2010 LED Transformations, LLC 59

Ambient = 40OC

Power = 10 W

Ventilated Insulated

Downlight

installed in

ceiling space

Results in a Tj

increase of

more than 15OC

The LED System

Thermal ConsiderationsAnd finally there is the environment


The LED System


Lifetime ConsiderationsHow long will LED-based luminaires last?

LED

100,000 hrs

LED

25,000 hrs

LED50,000 hrs

LED

5,000 hrs

LED

10,000 hrs


The LED System


• The sun >4.5 billion years (so far)

• Candle <12 hours

• Oil Lamp <24 hours

• Incandescent 1k-2k hours

• Fluorescent 5k-24k hours

• Mercury Vapor 10k-20k hours

• Sodium Vapor 24k hours

• Metal Halide 10k-20k hours

• 5mm LEDs <10k hours

• High Power LEDs >50k hours

Lifetime ConsiderationsHow long do light sources last?


The LED System

• Choose a statistically valid population of lamps

• Run them at specified ambient temperature

• Cycle them on/off at a prescribed pattern

• The time at which half the population has failed is considered the lifetime for that lamp

• Typically this process can take up to 15 months for lamps rated at 10,000 hours


Lifetime ConsiderationsHow do traditional lamp manufacturers measure lifetime?


The LED System

Since LEDs typically don’t fail catastrophically, but rather slowly dim, the industry has defined end of life to be the point at which the LED outputs 70% of the light it produced initially. The IESNA has published a standard LM-80 to define how to make lifetime measurements

Problems with that definition:

• Does 6,000 hours of testing accurately predict performance at 50,000 to 100,000 hours

• What about other performance characteristics such as color

• Many other components can cause a luminaire to degrade or fail prior to the LEDs reaching the 70% point


Lifetime ConsiderationsSo what is LED lifetime?


The LED System


Both manufacturers claim 50,000 hour lifetimes. Which one has the better likelihood of actually achieving that lifetime?

Lifetime Considerations


The LED System

Two identical high flux LEDs driven at the same drive current, but with an 11oC ambient temperature difference results in a expected lifetime difference of almost 3 X’s


Lifetime ConsiderationsEffect of junction temperature on lifetime


The LED System


60,000

50,500

27,000

11,000

InGaN Luxeon K2

Source: Philips White Paper “Understanding Power LED Lifetime Analysis”

At a junction temperature of 145oCthis LED would last:12k hours @ 1.5amps;27k hours @ 1.0amps;52k hours @ 0.7amps;and >60k hours @ 0.35amps

Lifetime ConsiderationsLifetime as a function of input current (at given Tj)


The LED System


light sources will last a long time if you take care of them. This one has been running for over 108 years!

Fire Station #6Livermore-Pleasanton Fire Department

What’s that spell?

Unlike many other light sources,LEDs don’t fail prematurely due to rapid on/off cycles. In fact, rapidly cycling LEDs on and off is one means of controlling their output intensity

Lifetime ConsiderationsEven incandescent….


The LED System

Beware of statements like: “Equivalent to a 60W bulb”

What does “equivalent” mean?

Puts out same number of lumens as a 60W bulb? OK

Same input power as a 60W bulb? FIRE the designer!

Same illuminance at the task area? OK

Looks like a 60W light bulb? Bet it costs more though!

Lasts as long as a 60W light bulb? FIRE the purchaser!

The question is really: “What are you comparing?”


Photometric ConsiderationsQuantity of Light – Lumens and Luminance


The LED System

Efficacy is a measure of how effective the light source is in converting electrical input power to lumen output, measured in lumens/Watt

Efficiency is simply the fraction of input electrical energy converted to light, independent of wavelength

Luminaire Efficiency is the percentage of lamp lumens that actually exit the fixture

Note: These terms are often used interchangeably


Photometric ConsiderationsQuantity of Light – LED efficacy vs. luminaire efficiency


The LED System

The small source (die) size allows for much better control of light output from LED sources as compared with other conventional light sources


LED Sources (75 lum/W)CU = 90%; Driver = 85%; Thermal = 90%

Luminaire efficiency = 52 lum/W

Incandescent Source (17 lum/W)Coefficient of Utilization = 60%

Luminaire efficiency = 10 lum/W

This allows for design of luminaires utilizing sources with less luminousflux (LEDs) that produce higher illuminance on a given surface thanconventional light sources

Photometric ConsiderationsQuantity of Light – Luminaire efficiency


The LED System

• Is the environment over lit?– How much is spec and how much

habit?

• How important is uniformity?

• What effect does CCT have on perception of brightness?

• Will users accept the sharp cut-off that LED sources can provide (e.g. street lights and sidewalks; lampshades in rooms)?


Photometric ConsiderationsQuantity of Light – Overall

PG&E Emerging Technologies

Cut-off Extremes


The LED System


Photometric ConsiderationsQuality of Light


The LED System

In 1943 David MacAdam analyzed the color differences of closely spaced points in the chromaticity diagram. He found that any two points must have a minimum

geometrical distance to yield a

perceptible difference in color.

Dividing the area of the chromaticity

diagram by the average area of a

MacAdam ellipse, shows that humans

can discern approximately 50,000

distinct chromaticities. If variations in

luminance are taken into account, this

number increases to greater than 106.


Plot for test subject PGNElipses shown 10 times actual size

Photometric ConsiderationsQuality of Light—MacAdam Ellipses


The LED System


Spectra of the 8 (14) color stand-ards used for calculating CRI

Photometric ConsiderationsQuality of Light – CRI

ΔEi = √ ΔUi2 + ΔVi

2 + ΔWi2

where U, V and W are the 1964Uniform Color Coordinates

Ri = 100 – 4.6 ΔEi

where Ri is the Color RenderingIndex for the specificcolor sample i

CRI = (1/8) x ∑ Ri

CRI is a calculated value based on the difference in chromaticity of a series of 8 (or 14) different colors (CIE Color Space) when illuminated with a reference light source versus a test subject light source.

It is a measure of a light source’s ability to show colors realistically as compared to familiar sources (e.g. an incandescent bulb or the sun)


The LED System


HID

FL

LED

IncandescentThe Sun

Irradiance of the Sun/Blackbody

0

500

1000

1500

2000

2500

200 300 400 500 600 700 800 900

Wavelength (in nm)

Po

wer

Den

sit

y (

rela

tive u

nit

s W

/m^3)

Above Atmosphere

Surface of Earth

Blackbody

Photometric ConsiderationsQuality of Light – Spectra of various light sources


The LED System

• Mixing Red, Green and Blue light yields white

• In the CIE diagram at left any color within the black lines would be possible with the three colors chosen


Photometric ConsiderationsQuality of Light – Creating white light via RGB combinations


The LED System

Downconverting Phosphor•Blue LED + YAG Cool White•Blue LED + YAG + Other phosphor (red, green, etc.) Warm White•UV LED + Red phosphor + Green phosphor + Blue phosphor


Heat Sink Slug

Submount

InGaN Die

Phosphor

Convention Coating Conformal Coating

Photometric ConsiderationsQuality of Light – Creating white light via phosphor conversion (PC)


The LED System


0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

400 450 500 550 600 650 700 750

Re

lati

ve F

lux

Wavelength (in nm)

Comparison of White LEDsfrom various Manufacturers Lumileds Cool White

Lumileds Warm White

Cree Cool White

Cree Warm White

Osram Cool White

Osram Warm White

Photometric ConsiderationsQuality of Light – Spectra of various LED sources

Source: Data sheetsfrom respectivemanufacturers


The LED System


Figure courtesy Mark McClear, Cree

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7 Step MacAdam Ellipses for DOE Energy Star CFLs

ANSI C78.377-2008 LED Standard

Photometric ConsiderationsQuality of Light – Binning for LEDs and CCT for CFLs


The LED System


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BBL+

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ANSI C78.377-2008 LED Standard

Figure courtesy Mark McClear, Cree

Photometric ConsiderationsQuality of Light – Mfg #2 CCT Offerings


The LED System


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90%

100%

400 450 500 550 600 650 700 750

Re

lati

ve S

pe

ctra

l In

ten

sity

Wavelength (in nm)

Change in Spectra Over Time

Initial

Lifetime

Overall effect is to shift CCThigher (toward blue)

Photometric ConsiderationsQuality of Light – CCT Shift Over Time


The LED System


Color possibilitiesat nominal valuesfor each LED:red (627)green (530)blue (470)

Desired white point

Photometric ConsiderationsQuality of Light – Potential Color Palate


The LED System


Color possibilitiesat potential limitsof each LED:red (620)green (550)blue (490)

Desired white point

Photometric ConsiderationsQuality of Light – Potential Color Palate (cont’d)


The LED System

• What LED color bins have been chosen for the product?– Does the luminaire manufacturer combine bins to get the desired

color temperature?

– How does the manufacturer compensate for color changes?

• Will the luminaire manufacturer be able to consistently supply those bins?– Do other manufacturers offer those same bins?

– What is the standard delivery time?

• What other industries use those same bins?– Will your luminaire manufacturer be the big or little fish?


Photometric ConsiderationsQuality of Light – Things to consider about binning

Standards For SSL

A Whole New Set of Rules


Standards for SSL


Measuring the Revolution

• Life

• Lumen Output

• Color Temperature (CCT)

• Color Rendering (CRI)

• Binning

• Power

• Efficiency/Efficacy

• Electrical

• Form Factors

• Safety


Standards for SSL


Measuring the Revolution

Committees galore– IESNA

– NEMA

– CIE

– UL

– ANSI

– DOE

– NGLIA

– NIST

– CSA

– IEC


Standards for SSL


Standards Development

• IESNA LM-79-08– Approved Method: Electrical and Photometric

Measurements of Solid-State Lighting Products Published May 2008

• IESNA LM-80-08– Approved Method for Measuring Lumen Depreciation of

LED Light Sources Published October 2008

• ANSI C78.377-2008– Specifications for the Chromaticity of Solid-State Lighting

Products for Electric Lamps Published February 2008


Standards for SSL


IESNA LM-79-08Approved Method: Electrical and Photometric Measurements of Solid-State

Lighting Products

• Absolute Photometry

• Type C Goniophotometer

• Total Luminous Flux

• Zonal Lumen Sums

• IES format file

• Spatial Uniformity of Color


Standards for SSL


LM-79—Type C Goniophotometer


• Zonal Lumen Sums

• IES Format File

• Spatial Uniformity of Color


Standards for SSL


LM-79—Integrating Sphere


• Spectral Power

• Distribution

• Chromaticity Coordinates

• CRI

• CCT


Standards for SSL


IESNA LM-80-08Approved Method for Measuring Lumen Depreciation of LED Light Sources

• Publication took almost a year longer than expected due to disagreements among stakeholders

• Lumen depreciation of devices, not the luminaires

• Measurements based on L70 and L50 at specific drive currents and case temperatures

• Case temperature is related to junction temperature


Standards for SSL


ANSI C78.377-2008Specifications for the Chromaticity of Solid State Lighting Products

• Purpose is to specify the range of chromaticities recommended for general lighting with Solid State Lighting products

• Ensure that white light chromaticities can be communicated to consumers

• Control circuitry and heat sinks incorporated in product

• Both fixtures incorporating light sources as well as integrated LED lamps

• Indoor lighting applications only

• Products that intentionally produce tinted or colored light not included

4 - 94

DOE Programs

• R&D Portfolio

• SSL Quality Advocate

• ENERGY STAR for SSL

• CALiPER• Standards Development

• Gateway Demonstration

• Design Competition

• Technical Information Network for SSL


Standards for SSL


Energy Star for SSL

• The Department of Energy has been working for a number of years to develop Energy Star criteria for Solid State Lighting

• Responsibility for Solid State Lighting Energy Star has now been taken over by the Environmental Protection Agency

• Unless the EPA changes the standards, requirements for SSL Energy Star products will ratchet up as the technology’s performance improves


Standards for SSL

Recommendations

How To Survive a Solid State Lighting Future


Recommendations

Lighting SystemsRequirements for a successful lighting system

Provide a complete product

• Quality of white light including color rendering, color temperature, radiation pattern, etc. Applications where the end-user must settle will be unsatisfactory no matter what “benefits” the product provides

• Consistency of light from fixture to fixture over temperature. In general, it is what the end-user is accustom to and expects

• Reliability >50k hours or more. It is a fundamental premise of Solid State Lighting and one of the few things that justify the higher cost

• Support in volume; Manufacturers promise a lot—the question is whether or not they can deliver

• Education of the customers including application engineering—so that they are applying the technology correctly to appropriate environments



Recommendations

Lighting SystemsObsolescence

• Haitz’s Law means a constantlychanging SSL industry– Changes are not just improved light output

• LED devices become obsolete (or available in limited quantities) as improved products come on the market– LED configurations are typically not interchangeable

– Different drive currents, forward voltages, optics, pcb layout, etc.

• This dynamic is not familiar to the general lighting industry– Edison-base light bulb has been around for over 100 years

– Fluorescents have been available since 1938

• If your projects have 3-4 year lead times before installation, will the luminaire you specified still be in production?



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US Electric Utility Rates

National Average = $0.104/kW-hr

Wyoming = $0.0629 / kW-hr

Hawaii = $0.2219 / kW-hr

Source: US Energy Information Administration (August 2009)

Recommendations

Wide Range of utility rates

• Energy Savings – depends on local cost of energy

• Maintenance Savings – depends on local labor costs (higher in areas such as New York City)– Other issues with maintenance such as dirt accumulation on luminaire

lenses, optics yellowing, etc. may affect results

– Long lifetime no maintenance

• Retrofit versus new construction – major difference in payback

• Safety stock?– Rapid changes in industry may limit ability to obtain identical fixtures in

the future


Calculating ROIItems to consider

Recommendations


Recommendations

Some Questions to Ask

1. Temperature range specification for operationHow does that compare with the maximum junction temperature for the LEDs used in the product?

2. Luminaire manufacturer- How long has the manufacturer been in business? What business?- Uses brand name LEDs?- Were the LEDs tested to LM-80?

3. Warranty- Life expectancy of product (Energy Star requires at least a 3 year

warranty)- What replacement costs are covered (e.g. installation labor, shipping,

etc.)- What performance elements are warranted (e.g. CCT shift, lumen

output, luminaire efficiency, etc.)


Recommendations

Some More Questions to Ask

4. Power Issues- Power Factor- Off-state power consumption (Energy Star requires < 0.5W)- Is the unit dimmable? With what controllers?

5. Does it have a UL / CSA / applicable safety mark?

6. Chromaticity- Shift over time/temperature- Variation from fixture to fixture

7. Luminaire performance- Fixture efficiency (in lumens/Watt)- Delivered lumens (not just LED device performance)- IES files- LM-79 test results from approved 3rd party laboratory- Lumen maintenance


Some LED Nutritional Information

Output

Wattage

Efficacy

CRI

CCT

Don’t settle for “Equivalent to a 50W MR-16, Par 38, etc.”

What’s Missing?

Lifetime

Recommendations


Acknowledgements

• Ron Bonne, Lumileds

• Ian Ferguson, University of NC Charlotte

• Shawn Keeney, Cree

• Mark McClear, Cree

• Steven Mesh, PG&E


Questions?

5 - 105


Thank YouContact Information:

Dr. John (Jack) W. CurranPresident LED Transformations, LLCPO Box 224 Stanton, NJ 08885 (908) [email protected]


mailto:[email protected]

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