LED LUMINAIRE LIFETIME: Recommendations for Testing and Reporting

UNDERSTANDING SSL LUMINAIRE LIFETIME 
Surprisingly to many, the true reliability and lifetime of light‐emitting diode (LED) lighting systems is currently unknown. Even worse, lumen maintenance values of LED devices are widely used as a proxy for the lifetime of an LED lighting system, which is misleading since light degradation or lumen maintenance is but one component of the reliability of a luminaire. For many manufacturers this approach cannot simply be ascribed to overly ambitious marketing efforts, but rather to dependence on anecdotal numbers in the absence of real data. In addition, we can impute simple ignorance in taking specifications at face value which may or may not live up to claims. It isn't just about the LED. Good LEDs can be incorporated into poorly engineered products and turn the Methuselah of lighting into the exponent of “live fast, die young.” The promise of LED lifetime is often presented in terms of hours and years but with little background data to support anything beyond vacuous promises. The statement of 100,000 hours of LED luminaire lifetime has given way to the realization that there is little consistency, very little published data, and few hard facts around so‐called luminaire lifetime numbers.  The situation is better at the LED package level, where reputable manufacturers have thousands of hours of data under varying conditions. But this is not enough. To manufacturers and specifiers in the solid‐state lighting (SSL) community, the dawning realization is that we need to work together towards understanding the issues surrounding true lifetime and reliability. We need to begin by cataloguing such failures and developing good models for underlying failure mechanisms. This process of understanding and explanation is very common in technological progress. Steam engines existed long before deep understanding of thermodynamic processes.  With LEDs, we have a substantial head‐start on the underlying physics and many years of experience in both lighting and semi‐conductors as well as reliability of related products.
There is no reason not to begin this journey and every reason to start. We will figure this out, find reliability methods and metrics, and learn the underlying root causes of failure. But without data, experiments and models, it is all conjecture. We need a program to drive to reliability metrics.
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