Lifetime and Reliability Long life has been billed as a key advantage of LEDs but understanding and communicating how LED products fail and how long they last can be challenging
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Lifetime and Reliability Long life has been billed as a key advantage of LEDs but understanding and communicating how LED products fail and how long they last can be challenging

While LEDbased products hold the potential to achieve lifetimes that meet or exceed their traditional counterparts manufacturer claims can be misconstrued by users who do not fully understand LED product failure mechanisms or the di57375erence betwe

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Lifetime and Reliability Long life has been billed as a key advantage of LEDs but understanding and communicating how LED products fail and how long they last can be challenging




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Presentation on theme: "Lifetime and Reliability Long life has been billed as a key advantage of LEDs but understanding and communicating how LED products fail and how long they last can be challenging"— Presentation transcript:


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Lifetime and Reliability Long life has been billed as a key advantage of LEDs, but understanding and communicating how LED products fail and how long they last can be challenging. While LED-based products hold the potential to achieve lifetimes that meet or exceed their traditional counterparts, manufacturer claims can be misconstrued by users who do not fully understand LED product failure mechanisms or the dierence between lifetime and reliability. Introduction

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BUILDING TECHNOLOGIES OFFICE CLEAN CITIES Figure 1. Failure rate (dotted lines) and percent remaining (solid lines) versus time for two hypothetical products. Reliability is the rate of random failure during the useful life phase, which is slightly lower (better) for the product shown in red. Using a 50% remaining metric for determining lifetime, the blue product has a longer rated life. Lifetime and reliability are not synonymous. The plots of failure rate illustrate the bathtub curve, which typically arises from some combination of design flaws, material and manufacturing defects, and

normal wear out. For LED products, design flaws may include insucient thermal management, poor driver design, or incompatible materials, among others. Material and manufacturing defects are the primary contributors to early failure, otherwise known as infant mortality, as well as failure during the useful life period. Some manufacturers attempt to reduce or eliminate early failures by utilizing a burn-in period prior to shipment. Products that are well designed and well made should reach normal end of life, an event that can be caused by one or more failure mechanisms. A

desirable product has a short early failure period (with failures that can be identified during infant mortality testing), a long useful life with a low rate of random failure (i.e., is highly reliable), and a short wear out period (consistent with steeper slopes in the bathtub curve), allowing for more predictable end- of-life planning. 2WKHUZD\VRIFRQYH\LQJOXPHQPDLQWHQDQFHSHUIRUPDQFHKDYH RSWLRQIRU/('/LJKWLQJ)DFWV

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BUILDING TECHNOLOGIES OFFICE CLEAN CITIES Figure 2. The distribution of failures over 34 million operating hours for one manufacturers family of outdoor

luminaires. A total of 29 fixtures failed out of more than 5,400 (0.56%). Source: Appalachian Lighting Systems, Inc. Important Terms Failure The end of useful life; may occur either catastrophically (i.e., burn out) or parametrically, where a product does not perform as intended (e.g., emits less than 70% of the initial output). Lifetime A statistical measure (or estimate) of how long a product is expected to perform its intended functions under a specific set of environmental, electrical and mechanical conditions. Lifetime specifications can only describe the behavior

of a population; any single product may fail before or after the rated lifetime. Mean Time Between Failures (MTBF) The average time between failures during useful life for repairable or redundant systems. Mean Time To Failure (MTTF) The average time to failure during useful life for components or non-repairable systems. Reliability A statistical measure (or estimate) of the ability of a product to perform its intended functions under a specific set of environmental, electrical, and mechanical conditions, for a specific period of time. Reliability estimates for the entire

useful life phase of a product are commonly reported using MTBF or MTTF. Serviceability The ability of a product to be repaired by regular maintenance personnel, typically through replacement of a subsystem or one or more associated components. Lifetime and Reliability PDWHRIKRZORQJDSURGXFWLVH[SHFWHGWRSHUIRUPLWVLQWHQGHG IXQFWLRQVXQGHUDVSHFLFVHWRIHQYLURQPHQWDOHOHFWULFDODQG

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UDWHPHWULFUHQGHULQJGLUHFWFRPSDULVRQEHWZHHQWKHWZRUDWLQJV ZKLOHDOLIHWLPHRIKRXUVPLJKWEHFRQVLGHUHGH[FHO OHQWDEDOODVWRUGULYHU07%)RIKRXUVPHDQVWKDWRYHU

D\HDUFRQWLQXRXVXVHIXOOLIHSHULRGRIWKHXQLWVZLOO OLNHO\IDLODQGQHHGWREHUHSODFHG Percent failures is equal to the period of use divided by the MTBF. In this case, 87,600 hours/100,000 hours  100% = 87.6%. DEOHV\VWHPVEXWVLQFH07%)RQO\GHVFULEHVDQDYHUDJHIDLOXUH Serviceability

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Discussion 7KHDFFXUDWHSRUWUD\DORI/('SURGXFWOLIHWLPHDQGUHOLDELOLW\

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Figure 3. In this theoretical example, the rated life of the LED system is a function of both the LEDs and the driver. The rated life of the combined system is approximately 52,000 hours, which is less than for either component individually. BUILDING TECHNOLOGIES OFFICE For more information, visit: ssl.energy.gov Direct fact sheet feedback to: SSL.Fact.Sheets@pnnl.gov  ġġĊĈĆăąƫƫđƫƫ1#10 .%*0!ƫ%0$ƫƫ.!*!(!ġ1.!ƫ%*'ƫ*ƫ,,!.ƫ*0%*%*#ƫ0ƫ(!0

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