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Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
Led Lifetime -- EDN Digikey at LFI 2010
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Led Lifetime -- EDN Digikey at LFI 2010

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  • 1. LED Lumen Maintenance & Lifetime Mark_McClear@cree.com May 13, 2010
  • 2. Copyright © 2010 Cree, Inc. pg. 2 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
  • 3. Copyright © 2010 Cree, Inc. pg. 3 Semiconductor Reliability Testing • Reliability test methods and acceptance criteria for semiconductor components have been standardized (JEDEC, EIAJ, others…) and practiced for decades – Think: processors, regulators, microcontrollers, etc.. If you’ve ever flown in an airplane, driven in a car, or spoken on a cell phone, you’ve depended on this body of scientific work and testing…
  • 4. Copyright © 2010 Cree, Inc. pg. 4 LED Reliability Testing • LEDs are semiconductor components that happen to emit light • Most LED manufacturers conduct the traditional standardized semiconductor component reliability testing on their LED lamps (http://www.cree.com/products/pdf/XLamp_Reliability.pdf) • 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 • Note: Lumen Maintenance ≠ LED Lifetime. Another standards committee – TM-21 – is working on that aspect of the problem
  • 5. pg. 5Copyright © 2010 Cree, Inc. Lumen Maintenance Definition 40% 50% 60% 70% 80% 90% 100% 110% 0 5 10 15 20 25 Operating Time (k hrs) LumenOutput(%) L70 = 10,000 hours Definition: change in light output of a light source over operational life, relative to initially measured light output Lxx = time to xx% of original light output • L70 = time to 70% of original light output • L50 = time to 50% of original light output Lumen Maintenance: Hypothetical HID Lamp Traditional light sources gradually dim then fail catastrophically (“burn out”)
  • 6. pg. 6Copyright © 2010 Cree, Inc. LED Lumen Maintenance Critical Parameters 1. TAIR Ambient Air Temperature 2. TJ Junction Temperature 3. TSP / TC / TS Solder-Point Temperature / Case Temperature 4. IF Forward Current / Drive Current
  • 7. Copyright © 2010 Cree, Inc. pg. 7 Low temp (25ºC) testing is a good surrogate for the LED chip depreciation – 1-2% @ TJ = 65ºC LEDs Last Forever! [under ideal conditions] At lower ambient air temperatures, LEDs hardly depreciate at all
  • 8. pg. 8Copyright © 2010 Cree, Inc. High Air Temperature Degrades Encapsulant • Cree now understands that the silicone-based encapsulants used in the industry degrade when exposed to high temperatures • Degradation comes from organic pendant groups (e.g. CH3, C6H5, -OH) that can off-gas or be trapped in the matrix • The higher the air temperature, the more the encapsulant will degrade, the more light lost OSiOSiOSi H–C–H H H–C–H H H–C–H H
  • 9. pg. 9Copyright © 2010 Cree, Inc. • The out-diffusion of volatiles from the silicone encapsulant causes the refractive index of the encapsulant to decrease • As the refractive index decreases the critical angle increases allowing less light to be emitted from the lamp (Snell’s Law) Un-powered LEDs Depreciate at High Temp
  • 10. pg. 10Copyright © 2010 Cree, Inc. 1,000 2,000 4,0003,000 5,000 6,000 7,0000 100 85 90 105 95 %LF Hours on Test Typical Behavior of LEDs on LM-80 Testing Low Air Temp High Air Temp
  • 11. pg. 11Copyright © 2010 Cree, Inc. Consistently Repeatable Behavior
  • 12. pg. 12Copyright © 2010 Cree, Inc. Cree XR-E XLamp 55°C LM-80 Testing
  • 13. pg. 13Copyright © 2010 Cree, Inc. Cree XR-E XLamp 55°C LM-80 Testing
  • 14. pg. 14Copyright © 2010 Cree, Inc. Cree XR-E XLamp 85°C LM-80 Testing
  • 15. pg. 15Copyright © 2010 Cree, Inc. Cree XP-E XLamp 55°C and 85°C LM-80 Testing
  • 16. pg. 16Copyright © 2010 Cree, Inc. Using the actual low temp test data at 6,000 hours, the projected L70 value is 63,917 hours. Projecting LED Lifetime Measured Data
  • 17. pg. 17Copyright © 2010 Cree, Inc. Using the actual low temp test data at 10,600 hours, L70 increases to 109,903 hours. Projecting LED Lifetime Measured Data
  • 18. pg. 18Copyright © 2010 Cree, Inc. When using the low temp 34,800 hour data, the L70 increases to > 200,000 hours! Projecting LED Lifetime Measured Data Exponential Curve-fit is inaccurate and exceedingly conservative
  • 19. pg. 19Copyright © 2010 Cree, Inc. So, How to Translate Lumen Maintenance to Lifetime…? • Cree has accumulated millions of XLamp XR-E LED lamp device hours of long-term data under both LM-80-compliant conditions and other test configurations • The effects of TAIR, TJ, TSP and IF on long-term lumen maintenance in this system have been closely studied and are well understood • Cree has observed that the lumen maintenance characteristics of the XLamp XR-E white LED lamps are different in the first 5,000 hours (called Period A) than in the time period following 5,000 hours (called Period B) • A “best fit” algorithm was developed to accurately model this lumen maintenance behavior, based on the critical parameters TAIR, TJ, TSP and IF • This algorithm is likely to be different for every LED lamp system (e.g. XLamp XP, MC, Rebel, Dragon, NS6, etc…)
  • 20. pg. 20Copyright © 2010 Cree, Inc. Cree LED Lifetime Model • Degradation in first 5,000 hours is mostly due to degradation in the silicone encapsulant • After 5,000 hours, this mechanism drops out and the slower chip degradation dominates • We see no “B10” early life failures or catastrophic failures in our XLamp systems
  • 21. pg. 21Copyright © 2010 Cree, Inc. 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000 110,000 120,000 130,000 140,000 150,000 60 70 80 90 100 110 120 130 140 150 160 MeanL70Lifetime(hours) Junction Temperature (ºC) Cree XLamp XR-E White L70 Lifetime Prediction - TAIR = 35ºC If = 350 mA If = 700 mA If = 1000 mA XLamp XR-E Lumen Maintenance Projection Given the Air (ambient) temp inside the fixture, drive current, and junction temperature, the lifetime is projected Note: 35ºC Air Temp
  • 22. pg. 22Copyright © 2010 Cree, Inc. 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000 110,000 120,000 130,000 140,000 150,000 60 70 80 90 100 110 120 130 140 150 160 MeanL70Lifetime(hours) Junction Temperature (ºC) Cree XLamp XR-E White L70 Lifetime Prediction - TAIR = 45ºC If = 350 mA If = 700 mA If = 1000 mA XLamp XR-E Lumen Maintenance Projection Note: 45ºC Air Temp
  • 23. pg. 23Copyright © 2010 Cree, Inc. 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000 110,000 120,000 130,000 140,000 150,000 60 70 80 90 100 110 120 130 140 150 160 MeanL70Lifetime(hours) Junction Temperature (ºC) Cree XLamp XR-E White L70 Lifetime Prediction - TAIR = 55ºC If = 350 mA If = 700 mA If = 1000 mA XLamp XR-E Lumen Maintenance Projection Note: 55ºC Air Temp
  • 24. pg. 24Copyright © 2010 Cree, Inc. 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000 110,000 120,000 130,000 140,000 150,000 60 70 80 90 100 110 120 130 140 150 160 MeanL70Lifetime(hours) Junction Temperature (ºC) Cree XLamp XR-E White L70 Lifetime Prediction - TAIR = 65ºC If = 350 mA If = 700 mA If = 1000 mA XLamp XR-E Lumen Maintenance Projection Note: 65ºC Air Temp
  • 25. pg. 25Copyright © 2010 Cree, Inc. 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000 110,000 120,000 130,000 140,000 150,000 60 70 80 90 100 110 120 130 140 150 160 MeanL70Lifetime(hours) Junction Temperature (ºC) Cree XLamp XR-E White L70 Lifetime Prediction - TAIR = 75ºC If = 350 mA If = 700 mA If = 1000 mA XLamp XR-E Lumen Maintenance Projection Note: 75ºC Air Temp
  • 26. pg. 26Copyright © 2010 Cree, Inc. XLamp XR-E Lumen Maintenance Projection 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000 110,000 120,000 130,000 140,000 150,000 60 70 80 90 100 110 120 130 140 150 160 MeanL70Lifetime(hours) Junction Temperature (ºC) Cree XLamp XR-E White L70 Lifetime Prediction - TAIR = 85ºC If = 350 mA If = 700 mA If = 1000 mA Note: 85ºC Air Temp
  • 27. pg. 27Copyright © 2010 Cree, Inc. XLamp XR-E Lifetime Projection There’s Nothing Magic about 50,000 • Models err on the conservative side • As much as we’d like it, there is no “one-number” answer (like CRI)
  • 28. pg. 28Copyright © 2010 Cree, Inc. 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000 110,000 120,000 130,000 140,000 150,000 60 70 80 90 100 110 120 130 140 150 160 MeanL70Lifetime(hours) Junction Temperature (ºC) Cree XLamp XR-E White L70 Lifetime Prediction - IF = 700mA Tair = 45C Tair = 55C Tair = 65C Tair = 75C Tair = 85C XLamp XR-E Lumen Maintenance Projection Note: 700mA IF
  • 29. pg. 29Copyright © 2010 Cree, Inc. 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000 110,000 120,000 130,000 140,000 150,000 60 70 80 90 100 110 120 130 140 150 160 MeanL70Lifetime(hours) Junction Temperature (ºC) Cree XLamp XR-E White L70 Lifetime Prediction - IF = 1000mA Tair = 45C Tair = 55C Tair = 65C Tair = 75C Tair = 85C XLamp XR-E Lumen Maintenance Projection Note: 1000mA IF
  • 30. pg. 30Copyright © 2010 Cree, Inc. 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: Can be the weak link in the system if cheap components are used Heat Sink: Linchpin of the entire system. If this is poorly designed, all the other components can be compromised
  • 31. Copyright © 2010 Cree, Inc. pg. 31 LED Lumen Maintenance & Lifetime Summary • Testing and characterizing LED lumen maintenance is an evolving science based on decades of work from the component semiconductor industry • LED Lumen Maintenance ≠ LED Lifetime • We have fully characterized the XLamp XR-E LED lamp and have developed an accurate predictive model for both the Lumen Maintenance and Lifetime of this lamp system • Key input variables to Lumen Maintenance and Lifetime are: – LED junction temperature (TJ) – calculated from TSP – Forward drive current (IF) – Air temperature around the lamp (TAIR) • From these, L70 and Lifetime of the LED lamp can be predicted with confidence • Different LEDs will likely have different lifetime models (TM-21) • LED Lifetime ≠ Luminaire Lifetime: need systems approach
  • 32. pg. 32Copyright © 2010 Cree, Inc.

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