led technology for lighting folks lightfair 08

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


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


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


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


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


Construction of LEDs

Standard 5mm LED

Epoxy body sometimes colored

Leads identified for polarityReflector maximises light

outputDie, semiconductor that

emits light


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


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


LED Colour

Each type of LED emits light in a narrow band widthGood for saturated colourLimited for RGB mixed white


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


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


Spectral Distribution of White

Cool White, 5000K

Warm White, 3500K


Ranges of White


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


LED Manufacturing Stages

Reasons for product variation

The WaferThe DieThe Package


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


Inspection and Measurement

Initial assessment of manufacturing successVisual Inspection


The Wafer

Wafer Maps


The Die

Wafer literally diced like carrots!Dies binnedFor colour (chromaticy)For forward voltageFor output


Packaging

Connections made to dieDie inserted in packageMany dies in same package

Device tested for:forward voltagecolour (chromacity)lumen output

LEDs then Binned


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


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


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


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!


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


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.


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


OLED State of the Art

At Frankfurt Light and BuildOsram prototype productIngo Maurer fixture


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


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


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


Questions?


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


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


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


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


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


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!


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


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


Optics

Multiple optic units simplify manufactureTertiary optic to vary distribution Specialized optics for particular applications


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


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


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


LED Fixtures

Manufacturers do different things as well!Board production

Pick and place machinesManual Assembly


Fixtures and Power Supplies

High degree of manual assemblyTesting also manual and basic


Quality Control

Vital part of the processLED binning for colourLED binning for outputOptical Alignment


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


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


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!


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


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.


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


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


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


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


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


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


Thank youand have fun with light!


Index

About SSLLED ManufactureWho Does WhatContinuous improvementStandardsReal Life PerformanceLED LifeTechnology ChangesThe FutureEnvironmental IssuesWhite Light LEDsConclusion


led technology for lighting folks lightfair 08

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