As SSL products are being rapidly introduced into the market, there is a need to develop standard screening and testing protocols that can be performed quickly and provide data surrounding product lifetime and performance. These protocols, derived from standard industry tests, are known as ALTs (accelerated life tests) and can be performed in a timeframe of weeks to months instead of years. Accelerated testing utilizes a combination of elevated temperature and humidity conditions as well as electrical power cycling to control aging of the luminaires. In this study, we report on the findings of failure modes for two different luminaire products exposed to temperature-humidity ALTs. LEDs are typically considered the determining component for the rate of lumen depreciation. However, this study has shown that each luminaire component can independently or jointly influence system performance and reliability. Material choices, luminaire designs, and driver designs all have significant impacts on the system reliability of a product. From recent data, it is evident that the most common failure modes are not within the LED, but instead occur within resistors, capacitors, and other electrical components of the driver. Insights into failure modes and rates as a result of ALTs are reported with emphasis on component influence on overall system reliability.
Although solid-state lighting (SSL) products are often intended to have product lifetimes of 15 years or more, the rapid change in technology has created a need for accelerated life tests (ALTs) that can be performed in the span of several months. A critical element of interpreting results from any systems-level ALT is understanding of the impact of the test environment on each component. Because of its ubiquity in electronics, the use of temperature-humidity environments as potential ALTs for SSL luminaires was investigated. Results from testing of populations of three commercial 6” downlights in environments of 85°C and 85% relative humidity (RH) and 75°C and 75% RH are reported. These test environments were found to accelerate lumen depreciation of the entire luminaire optical system, including LEDs, lenses, and reflectors. The effects of aging were found to depend strongly on both the optical materials that were used and the design of the luminaire; this shows that the lumen maintenance behavior of SSL luminaires must be addressed at the optical systems level. Temperature-Humidity ALTs can be a useful test in understand lumainaire depreciation provided that proper consideration is given to the different aging rates of various materials. Since the impact of the temperature-humidity environment varies among components of the optical system, uniform aging of all system components in a single test is difficult to achieve.
Solid-state lighting (SSL) luminaires containing light emitting diodes (LEDs) have the potential of seeing excessive temperatures during operation or during transportation and storage. Presently, the TM-21 test standard is used to predict the L70 life of SSL Luminaires from LM-80 test data. The underlying TM-21 Arrhenius Model is based on population averages, may not capture the failure physics in presence of multiple failure mechanisms, and does not predict the chromaticity shift. In this paper, Kalman Filter (KF) and Extended Kalman Filters (EKF) have been used to develop models for 70-percent Lumen Maintenance Life Prediction and chromaticity shift for a LEDs used in SSL luminaires. Ten-thousand hour LM-80 test data for various LEDs have been used for model development.
Nanofibers made from non-absorbing polymers such as poly(methyl methacrylate) are solid structures that have one
dimension (diameter) in the 10-1,000 nanometer (nm) range, while the other dimension (length) can be quite long.
These nanofibers can be formed in either an oriented or random packing structure, and the surface morphology of the
fiber can range from smooth to nanoporous. Quantum dots (QD) or other luminescent nanoparticles (diameter 1-10 nm)
can be added to the nanofiber to create the photoluminescent nanofiber (PLN). Because PLNs are nanocomposites of
fluorescent nanoparticles and polymer nanofibers, the optical properties of the nanocomposite, including absorption,
emission, and light scattering, can be tailored for application-specific requirements. Nanofibers may have several
applications in solid-state lighting, including serving as a light diffuser, providing optical filtering of low photopic
sensitive wavelengths (i.e., blue) to increase conversion to higher luminosity wavelengths, and providing a convenient
vehicle for handling and blending QDs to achieve a high color-rendering index.