Destroy in the Lab to Last in the Field – LED Robustness, Reliability and Life Time Testing

LpS 2018 - Lighting Quality & Testing
27 Sep 2018
10:30-11:00
Seefoyer

Destroy in the Lab to Last in the Field – LED Robustness, Reliability and Life Time Testing

“Among the many advantages of LEDs is their long lifetime. Lifetimes of 50 000h and more are expected and claimed which is equivalent to more than 10 years if operated for 12h per day. But how can one ensure or predict such a long time period?
The LM80 and TM21 are common standard requirements and methods to extrapolate the lifetime of LEDs for different forward current and temperature conditions. But seeing no degradation in the first 6000h hours does not guarantee that this trend will continue. How can one understand the behavior of LEDs over the complete lifetime without testing for 50 000h?
There are proven and well established methods of robustness and reliability testing which require a destructive testing of the LED under well-chosen overstress conditions in order to accelerate the aging of the LED in order to determine the typical aging behavior under lab conditions. These robustness tests are necessary to understand the failure mechanisms of the different parts of the LED and allow a detailed modelling of behavior under application conditions.
The lifetime of LEDs is not only determined by the degradation of the luminous flux but also by catastrophic failures of interconnections due to thermos mechanical stress and the damage of materials by hazardous atmospheres. Most influencing factors can be evaluated already in the lab under overstress conditions to predict a safe and solid operation under normal application conditions. Therefore one has to destroy the LED in the lab in order to ensure that it will last in the field.
LESSONS LEARNED
• Understanding the difference between robustness, reliability and lifetime testing
• Learn about the importance of destructive robustness testing for LEDs
• Understand the influencing factors of LED failure and their prediction
• Differentiate between lifetime extrapolation based on LM80 and TM21 and life time estimation based on life time models”