Transcript Document

Lumen Maintenance
Copyright © 2009 Cree, Inc.
pg. 1
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
Copyright © 2009 Cree, Inc.
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2 2
50,000 Hours Is
• Trivia Point: 50,000 hours is:
137
68.5
34.2
22.8
17.1
11.4
5.7
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Years at 1 hour/day
Years at 2 hours/day
Years at 4 hours/day
Years at 6 hours/day
Years at 8 hours/day
Years at 12 hours/day
Years at 24 hours/day
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LED Lumen Maintenance History
<1990
LEDs were used as indicators.
Lifetime did not matter too much.
1990’s
LEDs used for traffic signals and exit signs.
First basic studies on LED lifetime performed.
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
2009
IES LM-80-2008 is published
Copyright © 2009 Cree, Inc.
Cree publishes reliability white paper (TAIR)
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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
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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.
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L70 Lifetime Prediction – IF = 350 mA
How Do You
Know They
Last >50,000
Hours?
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L70 Lifetime Prediction – TAIR = 45ºC
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L70 Lifetime Prediction – TAIR = 55ºC
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L70 Lifetime Prediction – IF = 700 mA
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L70 Lifetime Prediction – IF = 700 mA
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L70 Lifetime Prediction – IF = 1000 mA
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40,000 Hour / 4.5 Year XLamp Long-Term Data
•
Lowambient
temp (25ºC)
testing is LEDs
a good
surrogate
for at all.
At lower
air temperature,
hardly
depreciate
the LED chip depreciation – 1-2% @ TJ = 65ºC
Copyright © 2009 Cree, Inc.
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System Lifetime is What Counts
System Lifetime is What Creates Value
Heat Sink: Linchpin of the entire system.
If this is poorly designed, all the other
components can be compromised
Driver: Much improvement on
rel and performance especially
with the large suppliers.
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
Copyright © 2009 Cree, Inc.
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Binning
Copyright © 2009 Cree, Inc.
pg. 15
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.
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Two Main Types of Binning
• Chromaticity or Color Binning
– Some defined “Box” in the
white area on or near the
Black Body Locus (White LEDs)
– Dominant Wavelength (Color
LEDs)
• Brightness or Flux Binning
– Minimum luminous flux or
radiant Flux
– Bin sizes (flux range)
varies by supplier
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Brightness or Flux Binning
Flux = total light emitted in all directions
Measured using an integrating sphere
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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
Flux:
102.3 lm
Driver
350 mA
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Chromaticity Binning
CCy: 0.35
CCx: 0.32
Driver
350 mA
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Design & Specification Strategies
Strategy #1
• Insist on the tightest bin
available
• Pay the highest price
possible
Copyright © 2009 Cree, Inc.
Strategy #2
• Understand light, binning,
and your application needs
• Do the mixing yourself in
your fixture if the
application will allow it
• Save money
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Design & Specification Strategies
Strategy #3
Let Cree do the mixing for
you...EasyWhite™
• Consistent color
• No complicated mixing recipes
• Reduced inventory
• Ease of manufacturing
Copyright © 2009 Cree, Inc.
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EasyWhite™
Copyright © 2009 Cree, Inc.
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