Report: LED Aging & Efficiency
DOE Study Examines Age-Related Changes in LED Device Efficiency and Optical Performance
The U.S. Department of Energy (DOE) has released a new study investigating age-related changes in light-emitting diode (LED) device efficiency and optical performance.
Lighting application efficiency (LAE)—the efficient delivery of light from the light source to the lighted task—is a useful way to identify and improve the energy productivity of LED technologies. Because of their high reliability, light source efficiency, and spectral tuning capabilities, LED lighting products are expected to exceed their conventional counterparts in LAE.
The new study aims to increase our understanding of the tradeoffs involved in optimizing the different elements of LAE: light source efficiency, optical delivery efficiency, spectral efficiency, and intensity effectiveness.
Conducted by RTI International, the study focuses on products with modified spectral output, because the method of spectral modification has a significant impact on the efficiencies in question. The report summarizes the findings from up to 8,000 hours of accelerated stress testing (AST) on lamp, LED light-engine, and downlight devices. The AST included high-temperature and wet high-temperature operation.
The findings show that the optimization of spectral efficiency can come at the cost of initial light source efficiency. Furthermore, the introduction of violet LEDs can promote long-term optical delivery efficiency degradation, and the introduction of optical filters or new phosphors can lead to unwanted spectral efficiency changes, because the ratio of phosphor emitters changes with aging.
Among the other key findings:
- Chromaticity maintenance of the products was generally good, with parametric failure only occurring for one product at one AST condition.
- Longer test times are needed to fully understand the luminous flux maintenance, luminous efficacy changes, and chromaticity shifts for some of the products.
- The study identified a common failure location in six-inch downlights.
The study results provide valuable information about changes to the light source, spectral, and optical delivery efficiencies as the devices age. This information can be used to improve future SSL designs.
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