Solid State Lighting Science & LED Theory of Operation David Cox December 2010
Learning  Objectives <ul><li>Basic intro to LED technology – specifically, White Lighting-class LEDs – and the critical en...
LED 101 Outline <ul><li>Basic LED Concepts </li></ul><ul><ul><li>Theory of operation </li></ul></ul><ul><ul><li>Materials ...
… A Brief History of Lighting 1879 Edison Light Bulb U.S. 223,898 <ul><li>Current lighting technology is about 100 years o...
One Problem to Address as an Industry… We  may not  [YET] know how to tell on SSL… <ul><li>We expect top quality, know how...
Not a Binning Problem (Poor LED Selection) The LED Matters 16.5 ”  Lowes Time zero 22” Linear LED Puck 16.5” Linear Copyri...
LED:  Theory of Operation <ul><li>LEDs consist of several layers of semiconductor material </li></ul><ul><li>Light is gene...
Materials of Construction * Guckes Indium Corporation; 22nd EU PV Solar Conference, Milan Italy 4Sep07, p.5-6   http://www...
LED Packages and Types Lamp Type Drive Current Light Output Brands Applications T1-type  (3 – 7 mm) 5 – 20 mA <1 – 4 lm (C...
Four Ways To Produce White Light with LEDs RGB Blue LED +  Phosphor <ul><li>Pros: </li></ul><ul><li>Tunable CCT, colors </...
Traditional Lamp vs. LED Technology <ul><li>From an applications standpoint, the most important differences are in: </li><...
<ul><li>LED Chip: </li></ul><ul><ul><li>Determines raw brightness and efficacy </li></ul></ul><ul><li>Phosphor system: </l...
Chip Architecture Features <ul><ul><li>A photon is a terrible thing to waste… </li></ul></ul><ul><ul><li>Surface Features ...
Raw Efficacy Enables More Applications  70 100 65 X X X X X 100 150 100 ? ? ? X X 175 250 150 50-60 20 ? ? ? Value 400 60-...
Implication #1 :  LEDs Are – Today – The most efficient commercially available white light source and improving all the ti...
LED Chips:  Analog Components <ul><ul><li>Light output and LPW efficacy varies with input drive current </li></ul></ul><ul...
LED Chips:  Size Doesn’t Matter <ul><ul><li>Small chips droop; Big chips droop </li></ul></ul><ul><ul><li>Small chips some...
Engineering Trade-off between: Phosphor Deposition Approaches <ul><li>Efficacy (LPW) </li></ul><ul><li>∆ CCT </li></ul><ul...
Typical Lighting-class LED Package <ul><ul><li>The LED Package provides: </li></ul></ul><ul><ul><li>Protection for the LED...
LED Packaging Trends <ul><li>Application-specific </li></ul><ul><li>Smaller size </li></ul><ul><li>Multiple high power chi...
Cree XLamp LED Product Portfolio – Lighting Copyright © 2010, Cree, Inc. pg.  LM-80 accepted LM-80 accepted LM-80 accepted...
∆ CCT <ul><li>Indoor linear applications are particularly sensitive to this and can benefit from an LED with good ∆CCT con...
Relative Advantages of the Approaches <ul><li>Small-chip,  dispersed phosphor </li></ul><ul><ul><li>Pros: </li></ul></ul><...
Describing Color:  Numbers & Words Spectral Power Distribution (~100 numbers) Chromaticity (xy or HSB)) (2-3 numbers) Colo...
Visible Light Spectrum  of Various Sources <ul><li>Which one is closer to the Sun? </li></ul><ul><li>Normalizing Incandesc...
Color Temperature Discrimination <ul><li>People’s ability to discern differences in color vary by CCT </li></ul><ul><li>Sp...
Color Rendering Index System 1 3000 4000 6000 2500 2 D65 <ul><li>First proposed in the 1950’s </li></ul><ul><li>Based on c...
CRI of Selected Light Sources 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Source CRI Low Pressure Sodium <5 High Pressure Sodium 20 R...
Color Rendering/Color Quality In Real Life CRI = 62 CRI = 93 CRI = 80 CRI = 92
<ul><li>David MacAdam – a scientist at Kodak – performed the first basic research in the late 1940’s </li></ul><ul><li>Fou...
Binning – Root Cause <ul><li>The human eye is extraordinarily sensitive, so small process variations in LED chip wavelengt...
Binning – Two Types <ul><li>Chromaticity binning </li></ul><ul><ul><li>Some defined “ box ” in the white area on or near t...
Luminous Flux Binning 119 lm 25ºC Driver 350 mA Flux:
Chromaticity Binning Driver 350 mA CCy: 0.41 CCx: 0.445 25ºC
LED Testing Conspiracy…? <ul><li>LEDs are manufactured in very high volume </li></ul><ul><li>LEDs go into a many different...
LED Bins in Context ANSI C78.377A ~4-step MacAdams ~7-step MacAdams ~2-step MacAdams Cree EasyWhite™ ~2/4-steps
LED Yield to Bin * For illustrative purposes only, not actual data Yield Loss Some bins zero yield
LED Color History 2006 ANSI C78.377-2008 3000K Quadrangle 2007 2009 2010 2-step 4-step
<ul><li>The LED junction is the area of the chip that actually creates  light.  Under normal operation, this area of the c...
Junction Temperature Calculation <ul><li>T J  = T SP  + R TH  * I F  * V F </li></ul><ul><ul><li>T SP  is solder point tem...
Thermal Path is Critical to LED Lifetime <ul><li>5mm lamps have almost no thermal path </li></ul><ul><li>R TH  >350ºC/W ty...
Trivia Point:  50,000 hours is: 137 Years at  1  hour/day 68.5 Years at  2  hours/day 34.2 Years at  4  hours/day 22.8 Yea...
LED Lifetime 40% 50% 60% 70% 80% 90% 100% 110% 0 10 20 30 40 50 60 70 80 90 100 Operating Time (k hrs) Lumen Output (%) 10...
Semiconductor Reliability Testing <ul><li>Reliability test methods and acceptance criteria for semiconductor components ha...
LED Reliability Testing <ul><li>LEDs are semiconductor  components that happen to emit light… </li></ul><ul><li>Most LED m...
LEDs Last Forever!!  [under ideal conditions] Well-designed systems with Lighting-class LEDs at low T A , T J  will run a ...
Predictive Algorithm *  Under Real Conditions <ul><li>Air Temperature (T A ) </li></ul><ul><li>Solder Point Temperature (T...
Typical Lighting-Class LED Lifetime
LED Lifetime Is Irrelevant System Lifetime is What Creates Value LED Lamps :  Practically never fail; depreciate very slow...
SSL Luminaire:  Multi-Disciplinary Effort Electrical <ul><li>Integrated systems approach required </li></ul><ul><li>LED li...
Lumens, LPW in the  REAL  World 1. Find 700mA point on relative intensity curve <ul><li>Typical LF should be: LF = 87.4 lm...
Lumens, LPW in the  REAL  World, p.2 <ul><li>3. Determine your thermal pad temperature (T sp ) </li></ul><ul><ul><li>Requi...
Lumens, LPW in the  REAL  World, p.3 <ul><li>Find 700mA on V F  curve V F  = 3.36V @  25 ºC </li></ul><ul><li>Calculate V ...
Optical Losses Secondary Optics 85%-90% Efficient 75%-95% Efficient Diffuser Reflector Lens
Driver Losses Generally, 80% - 85% is a good  estimate – but some will claim MUCH higher
Lumens, LPW in the  REAL  World, p.4 <ul><li>7. Assume: </li></ul><ul><ul><li>86% Efficient Diffuser </li></ul></ul><ul><u...
<ul><li>SSL generally outperforms CFL bulbs with higher rated lumens </li></ul><ul><ul><li>Tested delivered lumens using m...
Iterative Process:  More Power = More Light…
… But More Power = Lower Efficacy (Droop) 0% 20% 40% 60% 80% 100% 120% 140% 160% 180% 0 100 200 300 400 500 600 700 Drive ...
Wide Operating Range is Key to Optimization <ul><li>There is often an opportunity to trade-off drive current and thermal d...
Tools For Doing It:  Product Characterization Tool (PCT) www.cree.com/PCT
Real LED Levels of Performance ( Current ) <ul><li>Just like traditional lamps, ballasts and fixtures, LEDs have losses be...
Projected LED Levels of Performance  ( 2012 ) <ul><li>LEDs will be the most efficient mainstream light source available </...
SSL Standards (U.S.) <ul><li>4 years ago:  Major objection to LED </li></ul><ul><li>Today: </li></ul><ul><ul><li>RP-16 – S...
SSL Standards Status Status of NEMA, ANSI, IES, IEC, and CIE Solid State Lighting Standards (Partial List) Rev. 5-Aug-10 S...
ANSI Chromaticity Standard 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.40 0.41 0.42 0.43 0.44 0.45 0.30 0.31 0.32 0.33 ...
NEMA SSL-3 Binning Standard ANSI C78.377A SSL Chromaticity Standard New NEMA “SSL-3” Binning Standard Under Development
This Has Happened Before…. Vacuum Tubes VHS Film CRT TV Light Bulbs/ Fluorescent Tubes Transistors 1940s – 1960s DVD 1980s...
Moore’s Law for Transistor Cost -36%  CAGR
Four-year Lighting-class LED Snapshot <ul><li>>88% reduction in $/lm  (plus 65% LPW improvement) </li></ul><ul><li>100’s o...
Generic Outdoor SSL Economics Payback (years) 1 st  Gen BetaLED 10 5 SSL fixture technology improvement will have at least...
Final Thought… <ul><li>LED lighting systems can deliver real energy, real maintenance, and  real environmental  benefits –...
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  • Electroluminescence as different from incandescence – different phenomena require different management.
  • Restriction of Hazardous Substances Directive or RoHS, 2003 directive http://en.wikipedia.org/wiki/Restriction_of_Hazardous_Substances_Directive
  • This is another example of the difference between incandescence versus electroluminescence
  • This phenomenon occurs because IR is a frequency-dependent phenomenon – just like s sunset
  • Color Quality Scale
  • Might discuss 2 differenct notions of “sameness” – “Are these 2 same or different?” vs. “Make this one the same color as that one.”
  • Potential Lighting customers used to be able to use “no standards” as an excuse for waiting on SSL – not anymore. All the basic pieces are now in place. If we can agree on The basic definitions (what is an LED chip? Lamp? Light engine? Module?), and What color it is (ANSI), and How to measure it photometrically (LM79), and What the Lumen Maintenance of the LEDs are (LM80), and What are the safety standards for SSL (UL 8750) We then have the basis to conduct commercial business. Energy Star uses all of these standard, was enabled by this basic work, again pushed by the DOE funding…
  • This is an updated list of all the published standards and some of the important ones under development. We’re going to need another page soon!
  • Solid state lighting science and led theory of operation december 2010

    1. 1. Solid State Lighting Science & LED Theory of Operation David Cox December 2010
    2. 2. Learning Objectives <ul><li>Basic intro to LED technology – specifically, White Lighting-class LEDs – and the critical engineering disciplines required to design an LED luminaire </li></ul><ul><li>Develop a high-level understanding of the inter-disciplinary trade-offs needed when designing with LED light sources </li></ul><ul><li>Understand how LED brightness and color binning work, their strengths and limitations </li></ul><ul><li>Learn the role that proper thermal management, driver design, and optical design play in determining key operating parameters and lumen maintenance </li></ul>
    3. 3. LED 101 Outline <ul><li>Basic LED Concepts </li></ul><ul><ul><li>Theory of operation </li></ul></ul><ul><ul><li>Materials of construction </li></ul></ul><ul><ul><li>LED packages & types </li></ul></ul><ul><ul><li>LED technology </li></ul></ul><ul><ul><li>Color </li></ul></ul><ul><ul><li>Binning </li></ul></ul><ul><ul><li>LED reliability & lifetime projections </li></ul></ul><ul><li>LED Performance in the REAL world </li></ul><ul><li>LED standards status, cost trends </li></ul><ul><li>Final thoughts </li></ul>We’re Going To Get Our Hands Dirty
    4. 4. … A Brief History of Lighting 1879 Edison Light Bulb U.S. 223,898 <ul><li>Current lighting technology is about 100 years old </li></ul><ul><li>LEDs began as just indicators, but are now poised to become the most efficient light source ever created </li></ul>2008 Production White LED Lamp Exceeds 100 lm/W 1901 Fluorescent Tube ~1990 “ High Brightness” Red, Orange, Yellow, & Green LEDs 2000 White LED Lamp demonstrates Incandescent Efficacy (17 lm/W) 1919 Sodium Vapor Lamp 1970s First Red LED 1995 “ High Brightness” Blue, Green LEDs 2005 White LED Lamp demonstrates Fluorescent Efficacy (70 lm/W)
    5. 5. One Problem to Address as an Industry… We may not [YET] know how to tell on SSL… <ul><li>We expect top quality, know how to tell when we are getting it, and are willing to pay for it </li></ul><ul><li>We know extravagant marketing claims on this are not realistic </li></ul><ul><li>We know what we are getting when we buy a Yugo </li></ul>
    6. 6. Not a Binning Problem (Poor LED Selection) The LED Matters 16.5 ” Lowes Time zero 22” Linear LED Puck 16.5” Linear Copyright © 2010, Cree, Inc. pg. 97.8% Drop 1000 hours 84.1% Drop 96.9% Drop
    7. 7. LED: Theory of Operation <ul><li>LEDs consist of several layers of semiconductor material </li></ul><ul><li>Light is generated in the PN junction when a current is applied </li></ul><ul><li>Monochromatic (single color) light; must be down-converted with a phosphor </li></ul><ul><li>The color of light from the LED depends on the materials used </li></ul><ul><li>There are two material systems used to produce LEDs in all colors </li></ul><ul><ul><li>Red/Orn/Amber: AlInGaP </li></ul></ul><ul><ul><li>Green/blue: InGaN </li></ul></ul>
    8. 8. Materials of Construction * Guckes Indium Corporation; 22nd EU PV Solar Conference, Milan Italy 4Sep07, p.5-6 http://www.indium.com/_dynamo/download.php?docid=552 . <ul><ul><li>White, Lighting-class LEDs: </li></ul></ul><ul><ul><ul><li>… contain no mercury, metals </li></ul></ul></ul><ul><ul><ul><li>… utilize no rare or exotic materials </li></ul></ul></ul><ul><ul><ul><li>… save A LOT more energy in use than they consume in manufacturing </li></ul></ul></ul>http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/matthews_chicago09.pdf <ul><ul><li>… are RoHS compliant </li></ul></ul><ul><ul><li>… contain no substances of very high concern (SVHCs) as defined in the EU REACH program </li></ul></ul><ul><ul><li>… are “Article Exempt” from an EPA TSCA standpoint </li></ul></ul>
    9. 9. LED Packages and Types Lamp Type Drive Current Light Output Brands Applications T1-type (3 – 7 mm) 5 – 20 mA <1 – 4 lm (Commodity product) <ul><li>Indicators </li></ul><ul><li>Novelty lights </li></ul><ul><li>Traffic signals </li></ul><ul><li>Electronic signs </li></ul>Surface mount 5 – 20 mA 1 – 10 lm <ul><li>TopLED </li></ul><ul><li>SideLED </li></ul><ul><li>Cree CLA1A </li></ul><ul><li>Automotive </li></ul><ul><li>LCD backlighting </li></ul><ul><li>Electronic signs </li></ul>P4 20 – 100 mA 1 – 20 lm <ul><li>Piranha </li></ul><ul><li>Automotive </li></ul><ul><li>Channel letters </li></ul>High power 200-1500 mA 50-400 lm <ul><li>DRAGON </li></ul><ul><li>LUXEON </li></ul><ul><li>XLamp XPG </li></ul><ul><li>General illumination </li></ul><ul><li>Portable </li></ul><ul><li>Architectural </li></ul>Multi-small chip 200-700 mA 150-500 lm <ul><li>XLamp MX6 </li></ul><ul><li>XLamp MLE </li></ul><ul><li>General illumination </li></ul>Multi-power chip 200-1000 mA 300-3000 lm <ul><li>OSTAR </li></ul><ul><li>XLamp MPL </li></ul><ul><li>XLamp MCE </li></ul><ul><li>General illumination </li></ul>
    10. 10. Four Ways To Produce White Light with LEDs RGB Blue LED + Phosphor <ul><li>Pros: </li></ul><ul><li>Tunable CCT, colors </li></ul><ul><li>Any color possible </li></ul><ul><li>Cons: </li></ul><ul><li>Difficult to control </li></ul><ul><li>Low CRI (<50) </li></ul><ul><li>Lowest LPW efficacy (<40LPW*) </li></ul><ul><li>Pros: </li></ul><ul><li>Single LED type </li></ul><ul><li>Easy to control </li></ul><ul><li>Easy secondary optics </li></ul><ul><li>Good CRI (~82) </li></ul><ul><li>Cons: </li></ul><ul><li>OK efficacy (~40– 60LPW*) </li></ul><ul><li>Pros: </li></ul><ul><li>Highest efficacy (+20-30% v. blue + phos*) </li></ul><ul><li>Highest CRI (>90) </li></ul><ul><li>Cons: </li></ul><ul><li>Complicated to control </li></ul>Blue LED + “Remote” Phosphor + “ BSY” + Red <ul><li>Pros: </li></ul><ul><li>+5-10% efficacy v. blue + phos </li></ul><ul><li>Good CRI (~82) </li></ul><ul><li>Easy to control </li></ul><ul><li>Cons: </li></ul><ul><li>High cost due to complex LED binning </li></ul><ul><li>Rigid form factors </li></ul>* Achievable system efficacy @3000K, varies somewhat by application
    11. 11. Traditional Lamp vs. LED Technology <ul><li>From an applications standpoint, the most important differences are in: </li></ul><ul><ul><li>Directionality of generated light </li></ul></ul><ul><ul><ul><ul><ul><li>Omni-directional vs. directional </li></ul></ul></ul></ul></ul><ul><ul><li>Means of evacuating generated heat </li></ul></ul><ul><ul><ul><ul><ul><li>Convection vs. conduction </li></ul></ul></ul></ul></ul>Bulbs: Reflector (light) (heat) LEDs: <ul><ul><li>Note: Lighting-class LEDs provide a thermal path, typical through-hole LEDs do not </li></ul></ul>90 °-140° viewing angle (light) (heat) (light)
    12. 12. <ul><li>LED Chip: </li></ul><ul><ul><li>Determines raw brightness and efficacy </li></ul></ul><ul><li>Phosphor system: </li></ul><ul><ul><li>Determines color point and color point stability </li></ul></ul><ul><li>Package: </li></ul><ul><ul><li>Protects the chip and phosphor </li></ul></ul><ul><ul><li>Helps with light and heat extraction </li></ul></ul><ul><ul><li>Primary in determining LED lifetime </li></ul></ul>LED Technology
    13. 13. Chip Architecture Features <ul><ul><li>A photon is a terrible thing to waste… </li></ul></ul><ul><ul><li>Surface Features </li></ul></ul><ul><ul><li>Beveled saw cuts </li></ul></ul><ul><ul><li>Internal mirrors </li></ul></ul><ul><ul><li>Thin Film </li></ul></ul><ul><ul><li>Flip-chip </li></ul></ul>XT Metal bonding layer Backside ohmic contact metal n - AlInGaN Metal or semiconductor Metal bonding layer Backside ohmic contact metal Mirror layer Wire Bond Pad AlInGaN light emitting layer Backside ohmic contact metal SiC Mirror layer Wire Bond Pad AlInGaN light emitting layer Backside ohmic contact metal
    14. 14. Raw Efficacy Enables More Applications 70 100 65 X X X X X 100 150 100 ? ? ? X X 175 250 150 50-60 20 ? ? ? Value 400 60-70 20 40 ? 400 400 70-90 35 60 32 400 Value 90+ 50 75 32 400 Approx Wattage Equivalents 2007 2008 2009 2010 2011 2012 Parking Deck Roadway Downlights PAR lamps MR16 lamps A-lamps T8 lamps High Bay
    15. 15. Implication #1 : LEDs Are – Today – The most efficient commercially available white light source and improving all the time… <ul><li>Beyond saving real dollars on energy, a couple non-obvious things happen when the LEDs become more brighter and more efficient: </li></ul><ul><ul><li>Fewer LED are required for a given lighting application </li></ul></ul><ul><ul><li>Brighter LEDs enable penetrating higher and higher-volume lighting applications </li></ul></ul>Value MR16 2009 2011 2012 MR16 Volume by Wattage Technically Viable in
    16. 16. LED Chips: Analog Components <ul><ul><li>Light output and LPW efficacy varies with input drive current </li></ul></ul><ul><ul><li>Different LED types are BINNED at different currents </li></ul></ul><ul><ul><li>No such thing as “OVERDRIVING” an LED </li></ul></ul><ul><ul><li>Driving above (or below) the binning current is accepted and expected </li></ul></ul><ul><ul><li>Watch thermals and LM-80 data at high drive currents </li></ul></ul>Input Current (If, mA) Light Output, Efficacy Binning Current (mA) “ Droop” LPW efficacy Light Output Max Drive Current (mA)
    17. 17. LED Chips: Size Doesn’t Matter <ul><ul><li>Small chips droop; Big chips droop </li></ul></ul><ul><ul><li>Small chips sometimes appear to have higher efficacy since they are customarily binned higher up the droop curve </li></ul></ul><ul><ul><li>Primary real difference (not an advantage or disadvantage) is in the optics  very application-specific </li></ul></ul>* Typical data sheet of packaged LED lamp Chip Name Pic Chip Size (mm) Typical* Binning Current (mA) Current Density @ Binning Current (A/cm^2) Typical Light Output at Binning Current* (lm) Max Drive Current* (mA) Light Output @ Max Drive Current (lm) Current Density @ Max Drive Current (A/cm^2) TR 350 0.35x0.47mm 20 12.2 20 167 47 101.3 EZ700 0.7 x 0.7mm 350 71.4 94 500 139 102.0 EZ1000 1 x 1mm 350 35 114 1000 252 100.0 EZ1400 1.4 x 1.4mm 350 17.9 130 2000 551 102.0
    18. 18. Engineering Trade-off between: Phosphor Deposition Approaches <ul><li>Efficacy (LPW) </li></ul><ul><li>∆ CCT </li></ul><ul><li>Source size </li></ul><ul><li>Color Stability </li></ul><ul><li>Reliability </li></ul><ul><li>Cost </li></ul><ul><li>Binning </li></ul><ul><li>IP </li></ul><ul><li>Color </li></ul>4. Chip coating or plate 3. Conformal coating 1. Glob 2. Dispersed in encap
    19. 19. Typical Lighting-class LED Package <ul><ul><li>The LED Package provides: </li></ul></ul><ul><ul><li>Protection for the LED chip from the outside environment </li></ul></ul><ul><ul><li>Conductive path to carry generated heat away from the LED chip </li></ul></ul><ul><ul><li>RI matching from the LED chip to air </li></ul></ul><ul><ul><li>Reliability </li></ul></ul><ul><ul><li>Lens & encapsulant systems should not discolor under UV and exposure to high amounts of luminous flux </li></ul></ul>LED chip, RI~2.2 Substrate Air, RI = 1.0 Lens, RI ~1.4 Wire Bond Phosphor
    20. 20. LED Packaging Trends <ul><li>Application-specific </li></ul><ul><li>Smaller size </li></ul><ul><li>Multiple high power chips </li></ul><ul><li>Multiple small chips </li></ul><ul><li>Phosphor coatings vs. glob or dispersed </li></ul><ul><li>Higher wattage packages </li></ul><ul><li>Deposited silicone primary lens systems </li></ul><ul><li>“ Fried Eggs” </li></ul>Last Gen Packages New Gen Packages
    21. 21. Cree XLamp LED Product Portfolio – Lighting Copyright © 2010, Cree, Inc. pg. LM-80 accepted LM-80 accepted LM-80 accepted LM-80 accepted LM-80 accepted LM-80 accepted XLamp Single Die Multiple Die XR-C XR-E XP-C XP-E XP-G MX-6 MC-E MP-L Footprint (mm) 7.0 x 9.0 3.45 x 3.45 6.5 x 5.0 7.0 x 9.0 12 x 13 Max Current 500 mA Up to 1.0 A 500 mA 1.0 A 1.5 A 1000 mA 700 mA (per LED) 250 mA (per string) Viewing Angle 90° 90° 110° 115° 125° 120° 110° 125°
    22. 22. ∆ CCT <ul><li>Indoor linear applications are particularly sensitive to this and can benefit from an LED with good ∆CCT control </li></ul><ul><li>In general, Outdoor lighting is very forgiving on this </li></ul>
    23. 23. Relative Advantages of the Approaches <ul><li>Small-chip, dispersed phosphor </li></ul><ul><ul><li>Pros: </li></ul></ul><ul><ul><li>∆ CCT, uniformity of light </li></ul></ul><ul><ul><li>LM-80, Energy Star </li></ul></ul><ul><ul><li>Cons: </li></ul></ul><ul><ul><li>Limited drive capability </li></ul></ul><ul><ul><li>Generally higher V F </li></ul></ul><ul><ul><li>Large source size for secondary optics </li></ul></ul><ul><li>Large-chip, coated phosphor system </li></ul><ul><ul><li>Pros: </li></ul></ul><ul><ul><li>Much higher drive capability </li></ul></ul><ul><ul><li>Generally lower V F </li></ul></ul><ul><ul><li>Small source size; good for TIR optics </li></ul></ul><ul><ul><li>LM-80, Energy Star </li></ul></ul><ul><ul><li>Cons: </li></ul></ul><ul><ul><li>∆ CCT, uniformity of light </li></ul></ul><ul><li>Fried Eggs </li></ul><ul><ul><li>Pros: </li></ul></ul><ul><ul><li>Tons of light – thousands of lumens </li></ul></ul><ul><ul><li>Ease of use </li></ul></ul><ul><ul><li>Cons: </li></ul></ul><ul><ul><li>Lower efficacy </li></ul></ul><ul><ul><li>Thermal & binning challenges </li></ul></ul><ul><ul><li>No LM-80, Energy Star </li></ul></ul><ul><ul><li>Huge optical source </li></ul></ul>
    24. 24. Describing Color: Numbers & Words Spectral Power Distribution (~100 numbers) Chromaticity (xy or HSB)) (2-3 numbers) Color Temperature (1 number) “ Warm White” Descriptive Prose (Language)
    25. 25. Visible Light Spectrum of Various Sources <ul><li>Which one is closer to the Sun? </li></ul><ul><li>Normalizing Incandescent to CRI = 100 makes the CRI scale somewhat arbitrary </li></ul><ul><li>New standards – such as Color Quality System (CQS) is currently being considered for ALL light sources </li></ul>LED FL HID The Sun Incandescent
    26. 26. Color Temperature Discrimination <ul><li>People’s ability to discern differences in color vary by CCT </li></ul><ul><li>Specify your LEDs and design your systems tightly for indoor/warm colors; more loosely for outdoor/cooler CCTs </li></ul><ul><ul><li>3000K +/- 50K </li></ul></ul><ul><ul><li>4000K +/- 90K </li></ul></ul><ul><ul><li>5000K +/- 140K </li></ul></ul><ul><ul><li>6500K +/- 240K </li></ul></ul>Source: Wyszecki and Stiles, Color Science
    27. 27. Color Rendering Index System 1 3000 4000 6000 2500 2 D65 <ul><li>First proposed in the 1950’s </li></ul><ul><li>Based on color comparison of 8, then14 sample tiles with unsaturated colors </li></ul><ul><li>Incandescent bulbs are – by definition – CRI 100 </li></ul><ul><li>RGB LEDs have fully saturated colors and actually pay a mathematical penalty in the CRI system </li></ul>3 4 5 6 7 8 9 10 11 12 13 14
    28. 28. CRI of Selected Light Sources 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Source CRI Low Pressure Sodium <5 High Pressure Sodium 20 RGB LED (typical) 31 Mercury Vapor 43 Cool White Fluorescent 63 Metal halide 64 Cool White LED 70 Daylight Fluorescent 76 Warm White LED (YAG) 81 Tri-phosphor Fluorescent 82 F32T8 Tri-phosphor 85 BSY + R LED 93 Halogen MR16 99 Incandescent 100
    29. 29. Color Rendering/Color Quality In Real Life CRI = 62 CRI = 93 CRI = 80 CRI = 92
    30. 30. <ul><li>David MacAdam – a scientist at Kodak – performed the first basic research in the late 1940’s </li></ul><ul><li>Found a JND (Just Noticeable Difference) in color varied statistically by observer, size, and orientation in CIE 1931 </li></ul>MacAdam Ellipses Note: shown 10x actual size One Step (68.3%) Two Step (97.5%) Three Step (99.7%)
    31. 31. Binning – Root Cause <ul><li>The human eye is extraordinarily sensitive, so small process variations in LED chip wavelength; phosphor thickness, concentration, composition; and/or deposition conditions make a big perceived difference in white light CCT & quality </li></ul>Blue LED White Light Yellow Phosphor
    32. 32. Binning – Two Types <ul><li>Chromaticity binning </li></ul><ul><ul><li>Some defined “ box ” in the white area on or near the Black Body Locus </li></ul></ul><ul><ul><li>Bin sizes (x, y coordinates) varies by supplier </li></ul></ul><ul><li>Brightness or LF binning </li></ul><ul><ul><li>Minimum luminous flux (most suppliers) </li></ul></ul><ul><ul><li>Bin sizes/flux range varies by supplier </li></ul></ul>
    33. 33. Luminous Flux Binning 119 lm 25ºC Driver 350 mA Flux:
    34. 34. Chromaticity Binning Driver 350 mA CCy: 0.41 CCx: 0.445 25ºC
    35. 35. LED Testing Conspiracy…? <ul><li>LEDs are manufactured in very high volume </li></ul><ul><li>LEDs go into a many different applications and operating environments </li></ul><ul><li>Light output is diminished as a function of temperature </li></ul>NIST Comparison of Pulse vs. Steady-State * * Y. ZONG, Y. OHNO, National Institute of Standards and Technology, NEW PRACTICAL METHOD FOR MEASUREMENT OF HIGH-POWER LEDS, p.4, CIE SYMPOSIUM, July 2008 <ul><li>Therefore, LEDs are tested in the factory at ~20ms pulse at 25ºC testing rather than steady-state </li></ul><ul><li>A new IES LM standard is being proposed for pulse LED testing </li></ul>No Difference!
    36. 36. LED Bins in Context ANSI C78.377A ~4-step MacAdams ~7-step MacAdams ~2-step MacAdams Cree EasyWhite™ ~2/4-steps
    37. 37. LED Yield to Bin * For illustrative purposes only, not actual data Yield Loss Some bins zero yield
    38. 38. LED Color History 2006 ANSI C78.377-2008 3000K Quadrangle 2007 2009 2010 2-step 4-step
    39. 39. <ul><li>The LED junction is the area of the chip that actually creates light. Under normal operation, this area of the chip will get hot </li></ul>LED Junction Temperature (T J ) Running an LED above its rated maximum junction temperature will decrease its active lifetime and accelerate its lumen maintenance loss <ul><li>The LED junction temperature is affected by: </li></ul><ul><li>Ambient temperature of the LED’s immediate surroundings </li></ul><ul><li>Thermal path between the LED junction and ambient conditions </li></ul><ul><li>Power dissipated by the LED </li></ul><ul><li>The LED junction temperature is measured by: </li></ul><ul><li>Measuring the board temperature (Solder Point) adjacent to the LED (T SP ) </li></ul><ul><li>Computing the junction temperature (T J ) based on the drive current and data sheet parameters (R TH ) is straight-forward </li></ul>
    40. 40. Junction Temperature Calculation <ul><li>T J = T SP + R TH * I F * V F </li></ul><ul><ul><li>T SP is solder point temperature </li></ul></ul><ul><ul><li>R TH is the thermal resistance of the LED in ºC/Watt (LED datasheet) </li></ul></ul><ul><ul><li>I F is the forward current in Amperes </li></ul></ul><ul><ul><li>V F is the forward voltage in Volts </li></ul></ul><ul><li>Example: </li></ul><ul><ul><li>T SP = 60 ºC </li></ul></ul><ul><ul><li>R TH = 9 ºC/Watt (from data sheet) </li></ul></ul><ul><ul><li>I F = 700mA (0.7A) </li></ul></ul><ul><ul><li>V F = 3.2V  T J = 60 + [(9) * (0.7) * (3.2)] = 80 ºC </li></ul></ul>T SP
    41. 41. Thermal Path is Critical to LED Lifetime <ul><li>5mm lamps have almost no thermal path </li></ul><ul><li>R TH >350ºC/W typical </li></ul><ul><li>Chip (T J ) and phosphor can essentially cook themselves </li></ul><ul><li>Lighting-class LEDs are designed for high temp operation </li></ul><ul><li>R TH <10ºC/W typical </li></ul><ul><li>Lamp can stay within data sheet parameters with good thermal design </li></ul>Thermal path Lighting-class LED 5mm LED No Thermal path
    42. 42. Trivia Point: 50,000 hours is: 137 Years at 1 hour/day 68.5 Years at 2 hours/day 34.2 Years at 4 hours/day 22.8 Years at 6 hours/day 17.1 Years at 8 hours/day 11.4 Years at 12 hours/day 5.7 Years at 24 hours/day
    43. 43. LED Lifetime 40% 50% 60% 70% 80% 90% 100% 110% 0 10 20 30 40 50 60 70 80 90 100 Operating Time (k hrs) Lumen Output (%) 100 W Incandescent 5mm LED 42W CFL 50 W Tungsten Halide 400 W Metal Halide 25 W T8 Fluorescent Lighting-class LED <ul><li>Lighting-class LEDs become dimmer over time with no catastrophic failure </li></ul><ul><li>End of life defined by the LED becoming too dim – needed to define Lumen Maintenance (L 70 ) </li></ul><ul><li>Not all LED types have long lifetime </li></ul>Courtesy LRC, Rensellaer Polytechnic Institute
    44. 44. Semiconductor Reliability Testing <ul><li>Reliability test methods and acceptance criteria for semiconductor components have been standardized (JEDEC, EIAJ, others…) and practiced for decades </li></ul><ul><ul><li>Think: processors, regulators, microcontrollers, etc.. </li></ul></ul>If you’ve recently flown in an airplane, driven in a car, or talked on a cell phone, you’ve trusted your life on this body of scientific work and testing…
    45. 45. LED Reliability Testing <ul><li>LEDs are semiconductor components that happen to emit light… </li></ul><ul><li>Most LED manufacturers conduct standardized semiconductor component reliability testing – the same tests Intel tests their microprocessors with – on their LED lamps </li></ul><ul><li>The Illumination Engineering Society of North America published IES LM-80-2008 18 months ago to characterize the Lumen Maintenance aspect of LED semiconductor components </li></ul><ul><li>Note: Lumen Maintenance ≠ LED Lifetime. Another standards committee – TM-21 – is working on that aspect of the problem </li></ul>
    46. 46. LEDs Last Forever!! [under ideal conditions] Well-designed systems with Lighting-class LEDs at low T A , T J will run a very, very long time…
    47. 47. Predictive Algorithm * Under Real Conditions <ul><li>Air Temperature (T A ) </li></ul><ul><li>Solder Point Temperature (T SP ) </li></ul><ul><li>Junction Temperature (T J ) </li></ul><ul><li>Drive Current (I F ) </li></ul>Comprehends: * One of several under consideration by TM-21 committee
    48. 48. Typical Lighting-Class LED Lifetime
    49. 49. LED Lifetime Is Irrelevant System Lifetime is What Creates Value LED Lamps : Practically never fail; depreciate very slowly in a well-designed system Optical Components : Can (rarely) yellow over time and lose light; system design choice Driver : Currently the weakest point of the system, but the big companies are working on this Heat Sink : Linchpin of the entire system. If this is poorly designed, all the other components can be compromised
    50. 50. SSL Luminaire: Multi-Disciplinary Effort Electrical <ul><li>Integrated systems approach required </li></ul><ul><li>LED light is different than existing light technologies </li></ul><ul><li>Not intuitive at first </li></ul>Thermal <ul><li>These charts are on all LED data sheets; familiarization with them is essential to good results </li></ul>Optical Delivered lumens Delivered LPW
    51. 51. Lumens, LPW in the REAL World 1. Find 700mA point on relative intensity curve <ul><li>Typical LF should be: LF = 87.4 lm * 175% </li></ul><ul><li>LF = 154 lm EASY!! </li></ul>Case Study: Can Light, 650 lumens Warm white (3000K) XLamp XP-E, Q2 LF Bin (87.4 lm) 700mA I F
    52. 52. Lumens, LPW in the REAL World, p.2 <ul><li>3. Determine your thermal pad temperature (T sp ) </li></ul><ul><ul><li>Requires measurement </li></ul></ul>LF = 134 lm Assume T sp = 60°C LF = 154 lm * 87% EASY!! Case Study: Can Light, 650 lumens Warm white (3000K) XLamp XP-E, Q2 LF Bin (87.4 lm) 700mA I F
    53. 53. Lumens, LPW in the REAL World, p.3 <ul><li>Find 700mA on V F curve V F = 3.36V @ 25 ºC </li></ul><ul><li>Calculate V F @ 60 ºC from data sheet (T COV ) V F = V F@25ºC –(T COV (60-25)) V F = 3.36-(0.004(60-25)) V F = 3.22V @ 60 ºC </li></ul><ul><li>LPW = lumens / Watts </li></ul><ul><li>= lumens / V F * I F </li></ul><ul><li>= 134 / 3.22 * 0.7 </li></ul><ul><li>= 59.6 LPW </li></ul><ul><li>EASY (kind of…)!! </li></ul>Case Study: Can Light, 650 lumens Warm white (3000K) XLamp XP-E, Q2 LF Bin (87.4 lm) 700mA I F
    54. 54. Optical Losses Secondary Optics 85%-90% Efficient 75%-95% Efficient Diffuser Reflector Lens
    55. 55. Driver Losses Generally, 80% - 85% is a good estimate – but some will claim MUCH higher
    56. 56. Lumens, LPW in the REAL World, p.4 <ul><li>7. Assume: </li></ul><ul><ul><li>86% Efficient Diffuser </li></ul></ul><ul><ul><li>80% Efficient Driver </li></ul></ul>Delivered Lumens, LPW = 134 * 86% (optical loss) = 115 lumens = 115/3.22 * 0.7 = 51 LPW, 6 LEDs needed, ~650 lm = 51 LPW * 80% (driver loss) = 41 LPW (wall-plug, delivered LPW) Your Boss shows you press releases from LED companies and the spec sheets of LED luminaires from your competitors and wants to know why your design is so uncompetitive?
    57. 57. <ul><li>SSL generally outperforms CFL bulbs with higher rated lumens </li></ul><ul><ul><li>Tested delivered lumens using max lux from 9’8” height across variety of CFL sources and popular fixture and trim kit options </li></ul></ul><ul><ul><li>700lm SSL outperforms even 1750lm CFL on all but one configuration </li></ul></ul><ul><li>Tests demonstrate high delivered lumen efficiency of 700lm SSL </li></ul>Lumen Comparison: Rated vs. Delivered *Measured at 9.8ft height using high volume downlight fixture Maximum Lux*
    58. 58. Iterative Process: More Power = More Light…
    59. 59. … But More Power = Lower Efficacy (Droop) 0% 20% 40% 60% 80% 100% 120% 140% 160% 180% 0 100 200 300 400 500 600 700 Drive Current (mA) Relative Intensity (%) 0 10 20 30 40 50 60 70 Efficacy (lm/W) '
    60. 60. Wide Operating Range is Key to Optimization <ul><li>There is often an opportunity to trade-off drive current and thermal design for both system LPW (efficacy) and overall system cost </li></ul>I f (mA) 700 550 400 LPW 41 44 48 # of LEDs 6 7 9 Energy Star?   No     Cost $ $+ $++
    61. 61. Tools For Doing It: Product Characterization Tool (PCT) www.cree.com/PCT
    62. 62. Real LED Levels of Performance ( Current ) <ul><li>Just like traditional lamps, ballasts and fixtures, LEDs have losses beyond the boiler plate data sheet specs… </li></ul><ul><li>… but the source of losses are somewhat different: </li></ul><ul><ul><li>Thermal (also a source of Lumen Depreciation) </li></ul></ul><ul><ul><li>Optical (lenses, etc.) </li></ul></ul><ul><ul><li>Driver (electrical losses in power conversion) </li></ul></ul>
    63. 63. Projected LED Levels of Performance ( 2012 ) <ul><li>LEDs will be the most efficient mainstream light source available </li></ul><ul><ul><ul><li>>100 delivered LPW roadway light possible </li></ul></ul></ul><ul><ul><ul><li>Indoor fixtures >90LPW (wall-plug) </li></ul></ul></ul>
    64. 64. SSL Standards (U.S.) <ul><li>4 years ago: Major objection to LED </li></ul><ul><li>Today: </li></ul><ul><ul><li>RP-16 – SSL Definitions </li></ul></ul><ul><ul><li>ANSI C78.377 – chromaticity </li></ul></ul><ul><ul><li>IES LM-79-2008 – SSL photometry </li></ul></ul><ul><ul><li>IES LM-80-2008 – Lumen Maintenance </li></ul></ul><ul><ul><li>UL 8750 – Safety </li></ul></ul><ul><li>Most of the major pieces are in place, many more on the way… </li></ul><ul><li>Being practiced and referenced widely by industry and government programs </li></ul><ul><ul><li>RP-16 – SSL Definitions </li></ul></ul><ul><ul><li>ANSI C78.377 </li></ul></ul><ul><ul><li>LM-79 </li></ul></ul><ul><ul><li>LM-80 </li></ul></ul><ul><ul><li>UL 8750 </li></ul></ul>TBD
    65. 65. SSL Standards Status Status of NEMA, ANSI, IES, IEC, and CIE Solid State Lighting Standards (Partial List) Rev. 5-Aug-10 Standard Draft Comment Comment Resolution Publication Status IES RP-16 Definitions X X X Complete ANSI BSR C78.377A, Chromaticity X X X Complete IES LM 79, Luminous Flux X X X Complete IES LM 80, Lumen Depreciation X X X Complete NEMA LSD-44, 45, 49 (White Papers) Best Practices for SSL Interconnect, Sub-Assemblies, Dimming X X X Complete ANSI C82.77, Harmonic Emission Limits – Related Power Quality Requirements for SSL X X X Complete NEMA SSL-1, SSL Drivers X X X Complete NEMA SSL-3, LED Lamp Binning X X X NEMA SSL-4, Physical, Mechanical Standard for LED Retrofit Lamps NEMA SSL-6, Dimming Practices for SSL Integrated Lamps X NEMA SSL-6, Dimming Practices for SSL Integrated Lamps X NEMA-ALA Joint White Paper Definition of Functional & Decorative Lighting X X X Complete UL 8750 LED Safety X X X Complete IEC 62471-2, IES RP-27 Photobiological Safety X X X Complete IES TM-21 LED Lifetime X CIE TC1-69, Color Quality System X 47 CFR Part 15 (FCC) Radio Frequency Emissions for SSL Components, Drivers X X X Complete IEC 62471-2, IES RP-27 Photobiological Safety X X X Complete
    66. 66. ANSI Chromaticity Standard 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.40 0.41 0.42 0.43 0.44 0.45 0.30 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.40 0.41 0.42 0.43 0.44 0.45 0.46 0.47 0.48 0.49 0.50 CCx CCy BBL + 2700 K + 3000 K + 3500 K + 4000 K + 4500 K + 5000 K + 5700 K + 6500 K ANSI Fluorescent Lamp Standard ANSI C78.377A LED Standard
    67. 67. NEMA SSL-3 Binning Standard ANSI C78.377A SSL Chromaticity Standard New NEMA “SSL-3” Binning Standard Under Development
    68. 68. This Has Happened Before…. Vacuum Tubes VHS Film CRT TV Light Bulbs/ Fluorescent Tubes Transistors 1940s – 1960s DVD 1980s – 1990s Flat Panel TV and Displays 1990s – 2000s Flash Memory 1990s – 2000s Solid State Lighting 2000s – … “ Brick” phones Smart phones 1990s – 2000s
    69. 69. Moore’s Law for Transistor Cost -36% CAGR
    70. 70. Four-year Lighting-class LED Snapshot <ul><li>>88% reduction in $/lm (plus 65% LPW improvement) </li></ul><ul><li>100’s of Millions of Lighting-class LEDs shipped </li></ul><ul><li>Driven by brightness, package and process improvements & volume </li></ul>Cool White (6000K) Normalized $/lm XR 59 lm XR-E 80 lm XR-E 100 lm XP-E 110 lm XP-E 120 lm XP-G 130 lm -47% CAGR
    71. 71. Generic Outdoor SSL Economics Payback (years) 1 st Gen BetaLED 10 5 SSL fixture technology improvement will have at least as much impact as LED Technology 1 st Gen Cost of Ownership ($) Slope = energy $$ Maintenance Event First Cost MH CoO LED CoO 2 nd Gen BetaLED <ul><li>30% + efficacy </li></ul><ul><li>40% lower cost </li></ul>2 nd Gen
    72. 72. Final Thought… <ul><li>LED lighting systems can deliver real energy, real maintenance, and real environmental benefits – today – and performance is increasing all the time </li></ul><ul><li>Taking a multi-disciplinary approach – light source  driver  thermal  optics – is required to get quality results </li></ul><ul><li>You don’t have to be a “shade tree” mechanic to use LEDs – but for the time being, it is helpful… </li></ul>
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