IP, Reports & Roadmaps | Jul 21, 2011

DOE Publishes Updated Recommendations for Testing and Reporting LED Luminaire Lifetime

The U.S. Department of Energy (DOE) has published an updated version of the guide LED Luminaire Lifetime: Recommendations for Testing and Reporting, the latest edition in a series of publications on LED product performance and lifetime. The guide was developed by a working group under the auspices of DOE and the Next Generation Lighting Industry Alliance, composed of a diverse group of experts in reliability, lighting, and LED technology. Their recommendations are an important step toward consistent, industry-wide understanding of LED luminaire lifetime, and will assist standards organizations in their work.

What for the Guideline is intended:
Like the first edition of the guide, this second edition is a set of recommendations for reporting and demonstrating luminaire product lifetime. Initially, we sought to provide guidance for the Lighting Facts® program, which gives users, retailers, and manufacturers a common short-form reporting mechanism to improve the quality of solid-state lighting products on the market. The Lighting Facts label provides a summary of key performance criteria but does not include lifetime, for which there have been numerous requests. Ideally, it would be the addition of a single number, e.g., “eight years.” We attempted, in the first edition, to suggest some descriptions which would better describe lifetime, and it is fair to say that there are fewer wild claims in the marketplace. Yet there is still not an accepted protocol for measuring and characterizing lifetime. In part, this is due to cost, as a fair number of product samples must be tested to get good numbers, but it is also due in some measure to the industry’s early emphasis on lumen depreciation. Until recently, LED products have been described as “different” from conventional technologies—LEDs will just get dimmer until they fade away. But as we learn more about the behavior of these LED “systems,” it becomes evident that the life of a fixture may be considerably shorter than what is indicated by nominal light depreciation, albeit still generally longer than many incumbent lighting solutions.

This edition addresses a number of these issues and attempts to clarify the general understanding of reliability and how it pertains to lifetime; explore methods of estimating and characterizing lifetime; distinguish between types of failure and failure modes; look at differences between repairable and non-repairable systems; and revisit the definition of product life. It remains important to keep the SSL community focused on this issue. Cooperatively, it should be possible to develop sufficient data and best practices so that lifetime may be more accurately and more simply described.

These recommendations have been developed by a working group under the guidance of SSL Quality Advocates, a joint initiative of the DOE Solid-State Lighting Program and the Next Generation Lighting Industry Alliance (NGLIA). The working group is composed of members of NGLIA as well as other experts in reliability, lighting, and LED technology. As such, this guide is not an accepted international standard. Rather, it is meant to provide standards bodies with recommendations for their work in supporting the needs of the SSL community. These organizations will ultimately determine the details of the methods to measure and report the reliability of SSL luminaire products.

This guide covers only luminaire lifetime—i.e., changes over time —and does not address initial performance criteria or product consistency. Initial performance criteria for LED luminaires have been separately discussed in the December 2008 publication Reporting LED Luminaire Product Performance, found on the DOE SSL website at http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/led_productperformanceguide.pdf.

The "LED Luminaire Lifetime: Recommendations for Testing and Reporting" guidelines can be downloaded at http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/led_luminaire-lifetime-guide_june2011.pdf

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