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LED Technology for Lighting Folks
May 26, 14.00 to 17.00Kevan Shaw BSc IALD PLDA MSLL
1Tuesday, 27 May 2008
Learning Objectives
Understand the Manufacturing process of LEDs and the consequences for specific availability of LEDs in the market
Develop the ability to work out real life performance of LEDs and LED products from marketing information
Critically asses suitability for lighting tasks and create meaningful specifications
2Tuesday, 27 May 2008
What is Solid State Lighting?
Conventional Methods of converting electrical energy to light:
Heating up bits of wirePassing Electricity through gas at near vacuum Passing Electricity through gas above atmospheric pressure
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How About LEDs
Passing Electricity through small amounts of crystalline solidsSolid State deviceWorks well with other semiconductorsInitially used for panel indicators
Discovered in 1962 by Nick HolonyakIn 1963 he predicted white LEDS with 10X efficiency of
Incandescent
4Tuesday, 27 May 2008
Early LED colour
Initially red mass produced from 1969GaAsP Gallium Arsenide Technology produced red, amber and yellowearly green produced by IR and phosphorGaAIA Gallium Aluminum Arsenide High
brightness red LEDs from 1984
Shuji Nakamura of Nichia 1993InGaN Indium Gallium Nitride Technologyproduced blue and green
Allowed development of White LED
5Tuesday, 27 May 2008
Current Technology
Based on InGaN and AlAnGaPMany colours possible Colour varies with growth temperature of active layerEfficiency drops in GreenDifferent compositions behave differently
Reds and ambers have shorter life and greater colour shiftsBlues more stable, UV most stable
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Construction of LEDs
Standard 5mm LED
Epoxy body sometimes colored
Leads identified for polarityReflector maximises light
outputDie, semiconductor that
emits light
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Construction of LEDs
High output LEDs
Large die with reflectorMounted to Slug heat sinkLeads exit to side clear of light pathMoulded lens gathers and directs lightVarious distribution patterns Many different packages
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Heat Issues
Large heat sink necessaryLimit to efficiency of energy transferContained energy becomes heatEffective efficiency between 10% and 25%Largest surface area to volume most efficientShape important due to light trapped by total internal reflectionSmallest dies are most efficient but create least lumens
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LED Colour
Each type of LED emits light in a narrow band widthGood for saturated colourLimited for RGB mixed white
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White LEDs
Fluorescence; uses blue die with phosphorCombination of Blue from die and Yellow from phosphor gives
visual whiteColour not even across LEDWarmer colours less efficient
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Phosphor technology
Best is Itrium Aluminium Garnate CeriumProduces broad spectrum yellow90% efficient converting blue to yellowDeficient in Red
Strontium Sulphide EuropiumProduces increased redMuch less efficientCan create pink tinge in 2700K range
Importance of even thicknessConsistent colourMatch binning of phosphor with LEDRecent development of phosphor wafers or better control of
thickness
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Spectral Distribution of White
Cool White, 5000K
Warm White, 3500K
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Ranges of White
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White Light LEDs
Research goal to create white light directly from dieZnSe (Zinc Selenide) is a candidate technology not high outputDevelopment as Zinc Oxide nanostructure semiconductor RGB
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LED Manufacturing Stages
Reasons for product variation
The WaferThe DieThe Package
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The Wafer
Disk of the crystalline material that forms semiconductorGrown on mineral substrate: Epitaxy
Saphire, Silicone Carbide 2 or 6 diameterAim to use 12 Silicone for economy
Tightly controlled conditions to achieve uniform resultFirst layer grown at 1000CSecond at 700CFinal at 1000 C
Risk of changes to middle layer
Substrates flexVaries thickness of layers
Process takes 5 to 6 hours
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Inspection and Measurement
Initial assessment of manufacturing successVisual Inspection
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The Wafer
Wafer Maps
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The Die
Wafer literally diced like carrots!Dies binnedFor colour (chromaticy)For forward voltageFor output
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Packaging
Connections made to dieDie inserted in packageMany dies in same package
Device tested for:forward voltagecolour (chromacity)lumen output
LEDs then Binned
21Tuesday, 27 May 2008
Binning
Much discussed aspect of LEDsAt end of production line measurements made
fraction of a seconddevice at room temperature 25Cfully automated process
First stage of quality controlpossibly the most important
Aspects tested:ColorLumen OutputForward Voltage
22Tuesday, 27 May 2008
Heat Issues
Temperature in diedetermines LED survivaldetermines operating lifedetermines light outputdetermines efficiency
Higher the temperaturelower the lifelower light outputlower the efficiency
Critical temperature much lower than conventional lampsTH lamp pinch 350CLED internal temperatures 100C to 150C absolute maximum depends on
chip
23Tuesday, 27 May 2008
Who Does What?
All stages protected by patents that affect final productMultistage process undertaken by different companies When specified, LED usually already in fittingQuality and performance depends on integration in fittingFitting Manufacturer dependent on electronic component
suppliers stock availabilityStock availability depends on manufacture resultsForward selling to favored customers
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Standards
Manufacturers have failed the specifier and end userManufacturers create own standards
measurementbinningspecification criteria
We have to learn to interpret information presented in different formatsdo your own research!
25Tuesday, 27 May 2008
Technology changes
New chips available last year show 2X efficiency gainThis is after 2-3 years of slow changeNew technology, flip-chipSubstrate removed from die almost doubles light emitting areaEmitting Surface now at top of chipGood package and reflector design allows this light to be
emitted usefullyFurther major increases will require this kind of technical
advance.Internal Quantum efficiency now 80% Blue 20% Green 50% Red
26Tuesday, 27 May 2008
OLEDs
Use organic compounds rather than crystallinePotentially simpler to manufacturePrinting technique allows for complex patterns or arraysFlexible substrate:
Incorporate in clothRoll up light fixtures!
Technology development:Focused on flat panel displays & TVsLighting work funded by Govt.
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OLED issues
Limited life of organic material, 14,000 hours for blueSensitive to moisture and oxygen, sealing limits lifeCurrent efficiencies 10Lm/W to 20LmW same as incandescent!As power goes up colour goes green!CRI currently in 70s at best
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OLED State of the Art
At Frankfurt Light and BuildOsram prototype productIngo Maurer fixture
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OLED Opportunities
Flexible and not size limitedPossibility for complex arrays, colour/ pattern changingSimple printing techniques, potentially cheap productionTransparent substrates, at last the disappearing light-sourcePossibility for combining light and photo-voltaic
30Tuesday, 27 May 2008
Continuous Improvement
Another problem dressed up as an advantageTime scale of architectural projects longer than time for
changes in LEDsSpecified products frequently improved with new devices or
same device with improved outputCan create design problems with balance of light levels
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State of the Art
Best bins of best LEDs achieve efficiency of approx. 60LmWHighest output stock available LEDs produce:
Warm White Cree 73 Lm X 0.85 temp correction X 2.1 current = 130 Lm @1ACool White Cree 107 Lm X 0.85 temp correction X 2.1 current = 191 Lm @1AWarm White Luxeon 130Lm X .87 temp correction = 113Lm @1.5ACool White Luxeon 100Lm X .87 temp correction = 87 Lm@ 1A
Stock of best LEDs expensive and limitedFavoured markets, automotive etcForward purchasing, big companies
Stock Holdings:Luxeon RebelLuxeon K2TFFC
32Tuesday, 27 May 2008
Questions?
33Tuesday, 27 May 2008
LED Performance Data
Mostly measured at junction temperature of 25CData samples taken on a pulse of power too short to heat chip
Results in overstatement of performanceSimilar to tests for binning
Bins match published criteriaBins DO NOT match at operating conditions
Fitting manufacturers must re-bin at operating temperaturesOut of tolerance LEDs a problemProducts made in batches that match, but each batch differs
Difficulty in replacing faulty fittings to match originals
34Tuesday, 27 May 2008
Bases of Measurement
Light Output : LumensBased on Human visual response V() CurveColours in narrow wavelengths dont fit wellApparent output greater than indicated by measurement
Black PhotopicGreen Scotopic
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Colour Rendering Index
Originated in 1930s by CIEComparison between Black Body Radiator and Test Source
8 medium saturated colour samples 3 saturated, skin and leaf green
Range of colours selected for general illumination, works very well for fluorescent sourcesDoesnt work well for LEDS
National Institute of Standards and Testing, Yoshi OhnoProposal for new measure Color Quality Scale (CQS)Based on Saturated samples matched with source at same Color
Temperature
Test patch colours used for CRI
36Tuesday, 27 May 2008
How to Determine Real Life Performance
Manufacturers data not in common formatSimple fitting, 3W LED emergency light
- 60lm (min!) @ 25 driven at 700ma- Temperature de-rating :- with small heat sink at 48C assuming 16C/W Thermal
resistance of package gives Tj 90C = 78% = 47Lm
37Tuesday, 27 May 2008
How to Determine Real Life Performance
Manufacturers data not in common formatSimple fitting, 3W LED emergency light
- 60lm (min!) @ 25 driven at 700ma- Temperature de-rating :- with small heat sink at 48C assuming 16C/W Thermal
resistance of package gives Tj 90C = 78% = 47Lm
Fitting submitted to test housemeasured output 39.4 lm driven at 700ma LED only operating at 13lm/W
38Tuesday, 27 May 2008
Why the Discrepancy?
A crude experiment!An LED from the same batch left in freezer at -10C overnightMeasured at fixed point from a light meter gave 10LuxA few hours later when left running at room temperature 9LuxThen put in oven for a couple of hours at 100C 8luxNot a particularly good match for the published data!
39Tuesday, 27 May 2008
LED life
Early promises of 100,000 hours were wildly optimisticSome effort to standardize through ASSIST (Alliance for Solid
State Illuminations and Technologies)For illumination life is to 70% of initial LumensFor display life is to 50% of initial Lumens
40Tuesday, 27 May 2008
Optics
LEDs have built in basic optics.Lambertian distribution
Useful light distribution provided by separate optical elementsTypical distributions, spot, medium, wide and oval
Each type of LED requires unique opticsEach LED in fixture requires its own optic
Mounted at manufacture, not interchangeable
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Optics
Multiple optic units simplify manufactureTertiary optic to vary distribution Specialized optics for particular applications
42Tuesday, 27 May 2008
Environmental Issues
Price per lumen of LED exceeds all other lightsource$25 per KLm now, target for widespread adoption $5 per KLmIncan less than $1 KLm, Fluro $8 KLm Retail Pricesrevenues consumed by continuous development
Additional cost must be argued on basis oflow maintenancelow energy in use
System has finite life not always determined before installationwhole system will require replacement at end of life- Issues with WEEE for disposal and re-cycling
43Tuesday, 27 May 2008
Energy Efficiency
Much emphasis on energy in use to exclusion of other aspectsExample showed real world energy efficiency of 3 LmW!LEDs mostly Low Output for Low EnergyAnnouncements of LEDs achieving 130 LmW in lab testsNo data provided to protect intellectual property
conclusion that only very small or highly cooled LEDs can be this efficient
Order codes exist for 100 LmW chip at Tj25Cat Tj 90C = 80lm from data sheetavailable chips not to special order are 74 Lm/W at Tj 25Cat Tj 90C = 58lm therfore 58lm/W which is reasonable
44Tuesday, 27 May 2008
Manufacturing Issues
Form factor of LEDs vary by manufacturer and by technologylimited interchangeability fitting manufactures constantly need to redesign fittings and circuit
boards
Life of fitting determined by life of LED or Driverlife variable over wide rangeLEDs not individually replaceabletechnology shorter life than fittings
LED availability variablePreferred supply, automotive and aeronauticsProduction variable
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LED Fixtures
Manufacturers do different things as well!Board production
Pick and place machinesManual Assembly
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Fixtures and Power Supplies
High degree of manual assemblyTesting also manual and basic
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Quality Control
Vital part of the processLED binning for colourLED binning for outputOptical Alignment
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Determining Responsibility
Impossible to determine bin of LED installed on boardLED manufacturer cannot control thermal design of fittingsLight output, colour and life depend on thermal and electronic
designQuality and warranty claims difficult to resolveRectification frequently only possible by total replacement of
fitting
49Tuesday, 27 May 2008
The State of the Art
Acceptable efficiencies for General Lighting applicationsWide range of output and efficiencies for each deviceNo way of determining Bin Specification for installed deviceCost versus Output for different bins of same LEDInformation still requires working out to determine
performancePoor fitting output data for most manufacturers
50Tuesday, 27 May 2008
Lamp Replacement Products
Is this a good idea?MR16 replacement 8W 240LmDown-light retrofit 18 X 1W LEDsLED fluorescent replacementNone match full luminous
characteristics of lamp!
51Tuesday, 27 May 2008
Specific Functional LED products
2 X 2 lay in or pendent 56 X 1 W 1850LmNeo-Neon 33Lm/W actual efficiency
Task Light using High Output LEDs Luxo 11W LEDs to replace 18W CFL
Street LightingWe-ef optic covers street patternModular construction for maintenance
52Tuesday, 27 May 2008
How to Specify
Start with Lightsource - what do you want to achieve?White Light - Single source
Colour temperature?Colour quality, acceptable Bin RangeAcceptable variability, Direct view ? Mixed output?
White Light - Multi colourColour appearanceColour rendition3 source RGB or 4 source RGBA
Colour MixingSaturated colours RGBPastel colours or accurate matching RGBA or RGBW
Single colour Bin specification.
53Tuesday, 27 May 2008
Fixture Specification
Determine required light outputCheck fixture specification
Type of LEDDrive CurrentPhotometrics available of complete fitting?Calculated output? Check for temperature correction of LED specificationOptical design
Check thermal designDoes construction appear to provide adequate heat sinking?How hot does sample fitting get? Should be warm to touch but not too hot.
Manufacturer performanceTrack record in lighting?Experience with LEDs?Prepared to provide extended warranty
54Tuesday, 27 May 2008
System Design
Performance specification:Operating conditions
climate, particularly for outdoor fittingsInstallation, insulated voids? Airflow around fitting?
Visible outputFixtures lighting same surface?Fixtures directly viewed?
Control systemStandard protocol? DMXCompatible control gearDescribe operation in detail
Maintenance Future availability of fittings and LEDs?Are fittings repairable
55Tuesday, 27 May 2008
Controllability
LEDs easy to control - they are an electronic component!
Facades of light easy to doImagery allows architecture to
change day and nightReactive and interactive
surfaces, walls and ceilings
LEDs deliver colour easily and efficiently compared with other light sources
56Tuesday, 27 May 2008
The Future
Field of light products much more likely to be successfuloptimizes use of LED and existing backlight technologyopens possibilities for fittings not to be rectangular or circularno longer are fitting sizes restricted by set dimensions of lamps
First product recall, High efficiency LEDs recalled from fittings manufacturersProduction halted for 4 months
Line voltage LEDsSeol semiconductor Acriche2W & 4W 120V and 230V warm and cool white30LmW to 40 LmW headline efficacyNo transformer lossesSimplified Wiring
57Tuesday, 27 May 2008
The Future
Multi colour chips on same wafer - White by color mixingComplex circuits on chip - Acriche?Zinc Oxide Nanotechnology SemiconductorLED materials can also produce energy from light
LED detectors / emittersDevelopment of Photovoltaics using InGaN junctions
58Tuesday, 27 May 2008
Conclusion
LEDs increasingly common in lighting applicationsThey remain the most complex light-source to design and
specifyManufacturers are guardians of knowledgeBig players potential to monopolize design to installation
Professional Lighting Design community must learn morePersonal research and demanding information from suppliersProfessionals must determine the suitable light-source for every
applicationLEDs will never be the universal light-source for all applications
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Thank youand have fun with light!
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Index
About SSLLED ManufactureWho Does WhatContinuous improvementStandardsReal Life PerformanceLED LifeTechnology ChangesThe FutureEnvironmental IssuesWhite Light LEDsConclusion
61Tuesday, 27 May 2008
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