An LED luminaire is in many ways more complex than a traditional lighting fixture. It is an electromechanical system that includes, in addition to the essential light‐emitting source, provisions for heat transfer, electrical control, optical conditioning, mechanical support, and protection, as well as aesthetic design elements. Because the LEDs themselves are expected to have long life, all of these other components, adhesives, and other materials must be equally long‐lived, or, to the extent they are not, they will limit LED Luminaire Lifetime Recommendations,While LEDs do not radiate heat, with current products half or more of the input energy may be converted to heat that must be conducted away from the diodes. This situation requires a reliable, heat‐conducting assembly, be it mechanical or adhesive, in addition to a heat sink component or means for further conduction. For proper operation, the power supply and electronics must provide a well‐controlled DC drive current and possibly other control features, and must not fail for the life of the product.
Any optical components must be able to withstand years of exposure to intense light and possibly heat without yellowing, cracking, or other significant degradation. Reflecting materials need to stay in place and maintain their optical efficiencies.Even if the design itself has addressed all of these issues, questions of proper manufacturing remain. Was the epoxy properly mixed? Was an essential heat‐transmitting paste omitted? Were the wire bonds properly made? Any of the failure mechanisms inherent in electronic assemblies, and many others, may apply to an LED luminaire. Figure 1, above, is an attempt to visualize this
larger scope of SSL reliability.  For the best lifetime in a well‐designed and properly assembled luminaire, the principal failure mechanism should be lumen depreciation—a gradual reduction of light output from the packaged
LED over time. But other mechanisms could come into play. One LED vendor has reported that the principal causes for customer complaints involve either the use of chemicals in the luminaire that are incompatible with the LED or the driver overstressing the LED. These are design issues, but equally important are early failures of other components or subsystems or manufacturing defects.
These additional failure mechanisms will always persist to some degree and will usually lead to catastrophic failure, but they may sometimes simply accelerate lumen depreciation. An important message of this guide is that these mechanisms must be accounted for in describing product life.
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