copyright © 2009 cree, inc. pg. 1 lumen maintenance

Copyright © 2009 Cree, Inc. pg. 1

Lumen Maintenance


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


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


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.


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


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.


How Do You Know They

Last >50,000 Hours?

L70 Lifetime Prediction – IF = 350 mA


L70 Lifetime Prediction – TAIR = 45ºC


L70 Lifetime Prediction – TAIR = 55ºC


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


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


Binning


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.


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)


Brightness or Flux Binning

Flux = total light emitted in all directions

Measured using an integrating sphere


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:


Chromaticity Binning

Driver350 mA

CCy: 0.35CCx: 0.32


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


Let Cree do the mixing for you...EasyWhite™

• Consistent color

• No complicated mixing recipes

• Reduced inventory

• Ease of manufacturing

Strategy #3

Design & Specification Strategies


EasyWhite™

copyright © 2009 cree, inc. pg. 1 lumen maintenance

Documents

binning slide

ma slide

c slide

lumen maintenance slide

flux binning flux

ma flux

integrating sphere slide

luminous flux binning