1. Lumen Maintenance

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

3. 50,000 Hours Is 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
pg. 3

4. LED Lumen Maintenance History
1990’s LEDs used for traffic signals and exit signs. First basic studies on LED lifetime performed.
< LEDs were used as indicators. Lifetime did not matter too much.
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 standard
2007 Philips Lumileds publishes white paper, extending the knowledge of the industry on the topic (IF)
2008 IES LM is published
2009 Cree publishes reliability white paper (TAIR)

5. 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

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.

7. L70 Lifetime Prediction – IF = 350 mA
How Do You Know They Last >50,000 Hours?

8. L70 Lifetime Prediction – TAIR = 45ºC

9. L70 Lifetime Prediction – TAIR = 55ºC

10. L70 Lifetime Prediction – IF = 700 mA

11. L70 Lifetime Prediction – IF = 700 mA

12. L70 Lifetime Prediction – IF = 1000 mA

13. 40,000 Hour / 4.5 Year XLamp Long-Term Data
Low temp (25ºC) testing is a good surrogate for the LED chip depreciation – TJ = 65ºC
At lower ambient air temperature, LEDs hardly depreciate at all.
pg. 13

14. 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

15. Binning

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.

17. 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

18. Brightness or Flux Binning
Flux = total light emitted in all directions Measured using an integrating sphere

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
Driver 350 mA
Flux:
102.3 lm

20. Chromaticity Binning
CCy: 0.35
CCx: 0.32
Driver 350 mA

21. Design & Specification Strategies
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
Insist on the tightest bin available
Pay the highest price possible

22. Design & Specification Strategies
Let Cree do the mixing for you...EasyWhite™
Consistent color
No complicated mixing recipes
Reduced inventory
Ease of manufacturing
Strategy #3

23. EasyWhite™