LED Technology for Lighting Folks. May 26, to Kevan Shaw BSc IALD PLDA MSLL

Transcription

1 LED Technology for Lighting Folks May 26, to Kevan Shaw BSc IALD PLDA MSLL 1

2 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 2

3 What is Solid State Lighting? Conventional Methods of converting electrical energy to light: Heating up bits of wire Passing Electricity through gas at near vacuum Passing Electricity through gas above atmospheric pressure 3

4 How About LED s Passing Electricity through small amounts of crystalline solids Solid State device Works well with other semiconductors Initially used for panel indicators Discovered in 1962 by Nick Holonyak In 1963 he predicted white LEDS with 10X efficiency of Incandescent 4

5 Early LED colour Initially red mass produced from 1969 GaAsP Gallium Arsenide Technology produced red, amber and yellow early green produced by IR and phosphor GaAIA Gallium Aluminum Arsenide High brightness red LEDs from 1984 Shuji Nakamura of Nichia 1993 InGaN Indium Gallium Nitride Technology produced blue and green Allowed development of White LED 5

6 Current Technology Based on InGaN and AlAnGaP Many colours possible Colour varies with growth temperature of active layer Efficiency drops in Green Different compositions behave differently Reds and ambers have shorter life and greater colour shifts Blues more stable, UV most stable 6

7 Construction of LEDs Standard 5mm LED Epoxy body sometimes colored Leads identified for polarity Reflector maximises light output Die, semiconductor that emits light 7

8 Construction of LEDs High output LEDs Large die with reflector Mounted to Slug heat sink Leads exit to side clear of light path Moulded lens gathers and directs light Various distribution patterns Many different packages 8

9 Heat Issues Large heat sink necessary Limit to efficiency of energy transfer Contained energy becomes heat Effective efficiency between 10% and 25% Largest surface area to volume most efficient Shape important due to light trapped by total internal reflection Smallest dies are most efficient but create least lumens 9

10 LED Colour Each type of LED emits light in a narrow band width Good for saturated colour Limited for RGB mixed white 10

11 White LEDs Fluorescence; uses blue die with phosphor Combination of Blue from die and Yellow from phosphor gives visual white Colour not even across LED Warmer colours less efficient 11

12 Phosphor technology Best is Itrium Aluminium Garnate Cerium Produces broad spectrum yellow 90% efficient converting blue to yellow Deficient in Red Strontium Sulphide Europium Produces increased red Much less efficient Can create pink tinge in 2700K range Importance of even thickness Consistent colour Match binning of phosphor with LED Recent development of phosphor wafers or better control of thickness 12

13 Spectral Distribution of White Cool White, 5000K Warm White, 3500 K 13

14 Ranges of White 14

15 White Light LEDs Research goal to create white light directly from die ZnSe (Zinc Selenide) is a candidate technology not high output Development as Zinc Oxide nanostructure semiconductor RGB 15

16 LED Manufacturing Stages Reasons for product variation The Wafer The Die The Package 16

17 The Wafer Disk of the crystalline material that forms semiconductor Grown on mineral substrate: Epitaxy Saphire, Silicone Carbide 2 or 6 diameter Aim to use 12 Silicone for economy Tightly controlled conditions to achieve uniform result First layer grown at 1000 C Second at 700 C Final at 1000 C Risk of changes to middle layer Substrates flex Varies thickness of layers Process takes 5 to 6 hours 17

18 Inspection and Measurement Initial assessment of manufacturing success Visual Inspection 18

19 The Wafer Wafer Maps 19

20 The Die Wafer literally diced like carrots! Dies binned For colour (chromaticy) For forward voltage For output 20

21 Packaging Connections made to die Die inserted in package Many dies in same package Device tested for: forward voltage colour (chromacity) lumen output LEDs then Binned 21

22 Binning Much discussed aspect of LEDs At end of production line measurements made fraction of a second device at room temperature 25 C fully automated process First stage of quality control possibly the most important Aspects tested: Color Lumen Output Forward Voltage 22

23 Heat Issues Temperature in die determines LED survival determines operating life determines light output determines efficiency Higher the temperature lower the life lower light output lower the efficiency Critical temperature much lower than conventional lamps TH lamp pinch 350 C LED internal temperatures 100 C to 150 C absolute maximum depends on chip 23

24 Who Does What? All stages protected by patents that affect final product Multistage process undertaken by different companies When specified, LED usually already in fitting Quality and performance depends on integration in fitting Fitting Manufacturer dependent on electronic component supplier s stock availability Stock availability depends on manufacture results Forward selling to favored customers 24

25 Standards Manufacturers have failed the specifier and end user Manufacturers create own standards measurement binning specification criteria We have to learn to interpret information presented in different formats do your own research! 25

26 Technology changes New chips available last year show 2X efficiency gain This is after 2-3 years of slow change New technology, flip-chip Substrate removed from die almost doubles light emitting area Emitting Surface now at top of chip Good package and reflector design allows this light to be emitted usefully Further major increases will require this kind of technical advance. Internal Quantum efficiency now 80% Blue 20% Green 50% Red 26

27 OLEDs Use organic compounds rather than crystalline Potentially simpler to manufacture Printing technique allows for complex patterns or arrays Flexible substrate: Incorporate in cloth Roll up light fixtures! Technology development: Focused on flat panel displays & TVs Lighting work funded by Govt. 27

28 OLED issues Limited life of organic material, 14,000 hours for blue Sensitive to moisture and oxygen, sealing limits life Current efficiencies 10Lm/W to 20LmW same as incandescent! As power goes up colour goes green! CRI currently in 70s at best 28

29 OLED State of the Art At Frankfurt Light and Build Osram prototype product Ingo Maurer fixture 29

30 OLED Opportunities Flexible and not size limited Possibility for complex arrays, colour/ pattern changing Simple printing techniques, potentially cheap production Transparent substrates, at last the disappearing light-source Possibility for combining light and photo-voltaic 30

31 Continuous Improvement Another problem dressed up as an advantage Time scale of architectural projects longer than time for changes in LEDs Specified products frequently improved with new devices or same device with improved output Can create design problems with balance of light levels 31

32 State of the Art Best bins of best LEDs achieve efficiency of approx. 60LmW Highest output stock available LEDs produce: Warm White Cree 73 Lm X 0.85 temp correction X 2.1 current = 130 Cool White Cree 107 Lm X 0.85 temp correction X 2.1 current = 191 Warm White Luxeon 130Lm X.87 temp correction = Cool White Luxeon 100Lm X.87 temp correction = 87 Lm@ 1A Stock of best LEDs expensive and limited Favoured markets, automotive etc Forward purchasing, big companies Stock Holdings: Luxeon Rebel Luxeon K2TFFC 32

33 Questions? 33

34 LED Performance Data Mostly measured at junction temperature of 25 C Data samples taken on a pulse of power too short to heat chip Results in overstatement of performance Similar to tests for binning Bins match published criteria Bins DO NOT match at operating conditions Fitting manufacturers must re-bin at operating temperatures Out of tolerance LEDs a problem Products made in batches that match, but each batch differs Difficulty in replacing faulty fittings to match originals 34

35 Bases of Measurement Light Output : Lumens Based on Human visual response V(λ) Curve Colours in narrow wavelengths don t fit well Apparent output greater than indicated by measurement Green Scotopic Black Photopic 35

36 Colour Rendering Index Originated in 1930s by CIE Comparison 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 sources Doesn t work well for LEDS National Institute of Standards and Testing, Yoshi Ohno Proposal for new measure Color Quality Scale (CQS) Based on Saturated samples matched with source at same Color Temperature Test patch colours used for CRI 36

37 How to Determine Real Life Performance Manufacturer s data not in common format Simple fitting, 3W LED emergency light - 60lm 25 driven at 700ma - Temperature de-rating : - with small heat sink at 48 C assuming 16 C/W Thermal resistance of package gives Tj 90 C = 78% = 47Lm 37

38 How to Determine Real Life Performance Manufacturer s data not in common format Simple fitting, 3W LED emergency light - 60lm 25 driven at 700ma - Temperature de-rating : - with small heat sink at 48 C assuming 16 C/W Thermal resistance of package gives Tj 90 C = 78% = 47Lm Fitting submitted to test house measured output 39.4 lm driven at 700ma LED only operating at 13lm/W 38

39 Why the Discrepancy? A crude experiment! An LED from the same batch left in freezer at -10 C overnight Measured at fixed point from a light meter gave 10Lux A few hours later when left running at room temperature 9Lux Then put in oven for a couple of hours at 100 C 8lux Not a particularly good match for the published data! 39

40 LED life Early promises of 100,000 hours were wildly optimistic Some effort to standardize through ASSIST (Alliance for Solid State Illuminations and Technologies) For illumination life is to 70% of initial Lumens For display life is to 50% of initial Lumens 40

41 Optics LEDs have built in basic optics. Lambertian distribution Useful light distribution provided by separate optical elements Typical distributions, spot, medium, wide and oval Each type of LED requires unique optics Each LED in fixture requires its own optic Mounted at manufacture, not interchangeable 41

42 Optics Multiple optic units simplify manufacture Tertiary optic to vary distribution Specialized optics for particular applications 42

43 Environmental Issues Price per lumen of LED exceeds all other lightsource $25 per KLm now, target for widespread adoption $5 per KLm Incan less than $1 KLm, Fluro $8 KLm Retail Prices revenues consumed by continuous development Additional cost must be argued on basis of low maintenance low energy in use System has finite life not always determined before installation whole system will require replacement at end of life - Issues with WEEE for disposal and re-cycling 43

44 Energy Efficiency Much emphasis on energy in use to exclusion of other aspects Example showed real world energy efficiency of 3 LmW! LEDs mostly Low Output for Low Energy Announcements of LEDs achieving 130 LmW in lab tests No 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 Tj25 C at Tj 90 C = 80lm from data sheet available chips not to special order are 74 Lm/W at Tj 25 C at Tj 90 C = 58lm therfore 58lm/W which is reasonable 44

45 Manufacturing Issues Form factor of LEDs vary by manufacturer and by technology limited interchangeability fitting manufactures constantly need to redesign fittings and circuit boards Life of fitting determined by life of LED or Driver life variable over wide range LEDs not individually replaceable technology shorter life than fittings LED availability variable Preferred supply, automotive and aeronautics Production variable 45

46 LED Fixtures Manufacturers do different things as well! Board production Pick and place machines Manual Assembly 46

47 Fixtures and Power Supplies High degree of manual assembly Testing also manual and basic 47

48 Quality Control Vital part of the process LED binning for colour LED binning for output Optical Alignment 48

49 Determining Responsibility Impossible to determine bin of LED installed on board LED manufacturer cannot control thermal design of fittings Light output, colour and life depend on thermal and electronic design Quality and warranty claims difficult to resolve Rectification frequently only possible by total replacement of fitting 49

50 The State of the Art Acceptable efficiencies for General Lighting applications Wide range of output and efficiencies for each device No way of determining Bin Specification for installed device Cost versus Output for different bins of same LED Information still requires working out to determine performance Poor fitting output data for most manufacturers 50

51 Lamp Replacement Products Is this a good idea? MR16 replacement 8W 240Lm Down-light retrofit 18 X 1W LEDs LED fluorescent replacement None match full luminous characteristics of lamp! 51

52 Specific Functional LED products 2 X 2 lay in or pendent 56 X 1 W 1850Lm Neo-Neon 33Lm/W actual efficiency Task Light using High Output LEDs Luxo 11W LEDs to replace 18W CFL Street Lighting We-ef optic covers street pattern Modular construction for maintenance 52

53 How to Specify Start with Lightsource - what do you want to achieve? White Light - Single source Colour temperature? Colour quality, acceptable Bin Range Acceptable variability, Direct view? Mixed output? White Light - Multi colour Colour appearance Colour rendition 3 source RGB or 4 source RGBA Colour Mixing Saturated colours RGB Pastel colours or accurate matching RGBA or RGBW Single colour Bin specification. 53

54 Fixture Specification Determine required light output Check fixture specification Type of LED Drive Current Photometrics available of complete fitting? Calculated output? Check for temperature correction of LED specification Optical design Check thermal design Does construction appear to provide adequate heat sinking? How hot does sample fitting get? Should be warm to touch but not too hot. Manufacturer performance Track record in lighting? Experience with LEDs? Prepared to provide extended warranty 54

55 System Design Performance specification: Operating conditions climate, particularly for outdoor fittings Installation, insulated voids? Airflow around fitting? Visible output Fixtures lighting same surface? Fixtures directly viewed? Control system Standard protocol? DMX Compatible control gear Describe operation in detail Maintenance Future availability of fittings and LEDs? Are fittings repairable 55

56 Controllability LEDs easy to control - they are an electronic component! Facades of light easy to do Imagery allows architecture to change day and night Reactive and interactive surfaces, walls and ceilings LEDs deliver colour easily and efficiently compared with other light sources 56

57 The Future Field of light products much more likely to be successful optimizes use of LED and existing backlight technology opens possibilities for fittings not to be rectangular or circular no longer are fitting sizes restricted by set dimensions of lamps First product recall, High efficiency LEDs recalled from fittings manufacturers Production halted for 4 months Line voltage LEDs Seol semiconductor Acriche 2W & 4W 120V and 230V warm and cool white 30LmW to 40 LmW headline efficacy No transformer losses Simplified Wiring 57

58 The Future Multi colour chips on same wafer - White by color mixing Complex circuits on chip - Acriche? Zinc Oxide Nanotechnology Semiconductor LED materials can also produce energy from light LED detectors / emitters Development of Photovoltaics using InGaN junctions 58

59 Conclusion LEDs increasingly common in lighting applications They remain the most complex light-source to design and specify Manufacturers are guardians of knowledge Big players potential to monopolize design to installation Professional Lighting Design community must learn more Personal research and demanding information from suppliers Professionals must determine the suitable light-source for every application LEDs will never be the universal light-source for all applications 59

60 Thank you and have fun with light! 60

61 Index About SSL LED Manufacture Who Does What Continuous improvement Standards Real Life Performance LED Life Technology Changes The Future Environmental Issues White Light LEDs Conclusion 61