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4 Critical Factors That Affect LED Luminaire Reliability

The progress in solid state lighting technology has been breathtaking during the last few decades. As with many performance attributes, light emitting diodes (LEDs) have the potential to prevail over other technologies in terms of longevity. LED lighting manufacturers often claim their products to have long life, e.g., 50,000 hours or more, but this is misleading. Although LEDs have been widely established to have long operational life up to 100,000 hours or even more. LED luminaire life is not the same as the LED life. Unlike most other lighting technologies, LED lighting systems are electronic assemblies which have different components where degradation or failures can take place, in spite of the use of the durable LEDs. LED luminaire reliability is directly linked with other components in the luminaire and is determined by all its constitutive parts and their interactions upon environmental or operational stresses.

Driver (Power Supply)
A significant problem connected with the use of solid-state lighting relates to complications that arise in association with the driver that is utilized to power the LED light. The driver circuit is designed to properly manage the load and effectively supply the required low voltage power to the LEDs to ultimately produce light. The design of the driver circuit therefore becomes crucial in determining the performance of LED lamps. The most crucial parameters for an LED luminaire such as: lifespan, efficiency, power factor, harmonic distortions, dimming, and flickering depend, virtually exclusively, on the LED driver circuit's configuration and electrical performances.

Many reliability issues come down to component stresses as determined by factors such as abnormal environmental conditions, electrical operating parameter variations from surges, spikes, etc. An LED driver typically utilized a complex AC to DC circuit which may contain triodes, transformers, capacitors, rectifiers, transistors, and the like. Wherein the electronic elements such as triodes, transformers and electrolytic capacitors are sensitive to temperature. As temperature rises, their efficiency, lifetime and reliability will be substantially reduced.

Thermal Management
Thermal management for LED lighting systems, especially for high power LED lights is crucial to their performance and lifetime. When LEDs operate in a high-temperature environment and a space-limited housing, the heat generated by the LEDs can lead to overheating and premature failure of the luminaire. Further, overheating does not solely cause a problem to the LED packages, it can also lead to failures in one or more components of a driver that is integrated into the same enclosure with LEDs, and thus a malfunction or shut down of the entire system. To save material cost, e.g., on aluminum heat sinks, some manufacturers sacrifice fixture reliability, resulting in a much shorter life or even a potential safety hazard. A poor heat dissipation design is also the detrimental factor in overheating that leads to system failure.

Housing Integrity
The operation of an LED light is interdependent upon driver electronics, thermal management system, optical system, control gears, and electrical components. The entire system lasts only as long as these critical component are well protected. Failures from loss of housing integrity, ending up with moisture ingress, debris accumulation, structural failures, etc. Thermal management components, for example, may become less efficient as they accumulate dirt and debris. In outdoor applications, gaskets and other sealing materials may age prematurely due to poor quality of compatibility issues. This leads to moisture ingress and eventually damages the lighting system.

LED Light Sources
The LED package today is unquestionably a highly reliable component and is less likely to be the dominant factor behind system failure. With an optimized driving circuit, thermal management, and system design, LEDs rarely have catastrophic or parametric failure. The two main concerns associated with LED packages are the gradual failures as a consequence of lumen depreciation and color shift. Even though, these gradual failures are foreseeable and already considered in the luminaire system design.
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