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Copyright © 2009 Cree, Inc. pg. 1
Lumen Maintenance
Copyright © 2009 Cree, Inc. pg. 2
Lumen Maintenance Definition
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
pg. 2
Copyright © 2009 Cree, Inc. pg. 3
50,000 Hours Is
• Trivia Point: 50,000 hours is:
137 Years at 1 hour/day68.5 Years at 2 hours/day34.2 Years at 4 hours/day22.8 Years at 6 hours/day17.1 Years at 8 hours/day11.4 Years at 12 hours/day5.7 Years at 24 hours/day
pg. 3
Copyright © 2009 Cree, Inc. pg. 4
LED Lumen Maintenance History
<1990 LEDs were used as indicators.Lifetime did not matter too much.
2001 Lumileds (Philips) introduces first High Power LED. Lifetime testing gets more serious.
2004 LRC/ASSIST publishes first work on the topic.Basic science understood.
2006 LRC/ASSIST publishes ASSIST recommends test procedure for lifetime testing of High Power LEDs, which becomes the basis for IESNA LM-80-2008 standard
2007 Philips Lumileds publishes white paper, extending the knowledge of the industry on the topic (IF)
2008 IES LM-80-2008 is published
2009 Cree publishes reliability white paper (TAIR)
1990’s LEDs used for traffic signals and exit signs.First basic studies on LED lifetime performed.
Copyright © 2009 Cree, Inc. pg. 5
LED Lumen Maintenance Critical Parameters
1. TAIRAmbient Air Temperature
2. TJ Junction Temperature
3. TSP / TC / TSSolder-Point Temperature / Case Temperature
4. IFForward Current /Drive Current
Copyright © 2009 Cree, Inc. pg. 6
Cree Lumen Maintenance 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.
• Good quality LEDs in well-designed fixtures will last for decades under normal use and operating conditions.
Copyright © 2009 Cree, Inc. pg. 7
How Do You Know They
Last >50,000 Hours?
L70 Lifetime Prediction – IF = 350 mA
Copyright © 2009 Cree, Inc. pg. 8
L70 Lifetime Prediction – TAIR = 45ºC
Copyright © 2009 Cree, Inc. pg. 9
L70 Lifetime Prediction – TAIR = 55ºC
Copyright © 2009 Cree, Inc. pg. 10
L70 Lifetime Prediction – IF = 700 mA
Copyright © 2009 Cree, Inc. pg. 11
L70 Lifetime Prediction – IF = 700 mA
Copyright © 2009 Cree, Inc. pg. 12
L70 Lifetime Prediction – IF = 1000 mA
Copyright © 2009 Cree, Inc. pg. 13
Low temp (25ºC) testing is a good surrogate for the LED chip depreciation – 1-2% @ TJ =
65ºC
40,000 Hour / 4.5 Year XLamp Long-Term Data
• At lower ambient air temperature, LEDs hardly depreciate at all.
pg. 13
Copyright © 2009 Cree, Inc. pg. 14
System Lifetime is What Counts
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: Much improvement on rel and performance especially with the large suppliers.
Heat Sink: Linchpin of the entire system. If this is poorly designed, all the other components can be compromised
Copyright © 2009 Cree, Inc. pg. 15
Binning
Copyright © 2009 Cree, Inc. pg. 16
What is LED binning?
Used to define similar groups of parts by performance characteristics
Not unlike other industries that bin based on performance, ie: microprocessor
Cree XLamp® LED binning based on two parameters:–Flux (total light output)–Chromaticity (white), Dominant wavelength (color)
Even fluorescent tubes are binned by chromaticity–“daylight”, “warm white”, etc.
Copyright © 2009 Cree, Inc. pg. 17
Two Main Types of Binning
•Brightness or Flux Binning– Minimum luminous flux or
radiant Flux
–Bin sizes (flux range) varies by supplier
•Chromaticity or Color Binning–Some defined “Box” in the white area on or near the Black Body Locus (White LEDs)– Dominant Wavelength
(Color LEDs)
Copyright © 2009 Cree, Inc. pg. 18
Brightness or Flux Binning
Flux = total light emitted in all directions
Measured using an integrating sphere
Copyright © 2009 Cree, Inc. pg. 19
Luminous Flux Binning
• LEDs are tested & sorted into luminous flux bins• Performance binning is very standard in the semiconductor
industry (e.g., CPUs), but confusing to the lighting industry where performance is very standardized
102.3 lm
Driver350 mA
Flux:
Copyright © 2009 Cree, Inc. pg. 20
Chromaticity Binning
Driver350 mA
CCy: 0.35CCx: 0.32
Copyright © 2009 Cree, Inc. pg. 21
Design & Specification Strategies
• Insist on the tightest bin available
• Pay the highest price possible
Strategy #1
• Understand light, binning, and your application needs
• Do the mixing yourself in your fixture if the application will allow it
• Save money
Strategy #2
Copyright © 2009 Cree, Inc. pg. 22
Let Cree do the mixing for you...EasyWhite™
• Consistent color
• No complicated mixing recipes
• Reduced inventory
• Ease of manufacturing
Strategy #3
Design & Specification Strategies
Copyright © 2009 Cree, Inc. pg. 23
EasyWhite™
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