Meeting the longevity requirements of solid-state lighting (SSL) devices places extreme demands on the materials and designs that are used in SSL luminaires. Therefore, understanding the aging characteristics of lens, reflectors, and other materials is essential to projecting the long-term performance of LED-based lighting systems. Overlooking these factors at either the design or product specification stage can result in premature failure of the device due to poor luminous flux maintenance and/or excessive chromaticity shifts. This paper describes a methodology for performing accelerated stress testing (AST) on materials intended for use in SSL luminaires. This test methodology, which consists of elevated temperature and humidity conditions, produces accelerated aging data that can be correlated to expected performance under normal luminaire operating conditions. The correlations can then be leveraged to produce models of the changes in the optical properties of key materials including transmittance versus wavelength of lenses and reflectance versus wavelength for housings and other reflectors. This information has been collected into a lumen maintenance decision support tool (LM-DST) and together with user supplied inputs (e.g., expected operation conditions) can provide guidance on lifetime expectations of SSL luminaires. This approach has been applied to a variety of materials commonly found in SSL luminaires including acrylics, polycarbonates, and silicones used for lenses and paints, coatings, films, and composites used for reflectors.

Results from accelerated life tests (ALT) on mass-produced commercially available 6" downlights are reported along with results from commercial LEDs. The luminaires capture many of the design features found in modern luminaires. In general, a systems perspective is required to understand the reliability of these devices since LED failure is rare. In contrast, components such as drivers, lenses, and reflector are more likely to impact luminaire reliability than LEDs.

Next to energy efficiency, long life is probably the most publicized of solidstate lighting’s (SSL) potential advantages, and plays a key role in any cost-benefit analysis. To accommodate the rapid evolution of SSL technologies and fully realize their energy-savings potential, there is a widespread need in the lighting industry to understand potential failure modes of luminaires. LED luminaires are composed of many working parts, each of which could impact product reliability, so a systems approach is needed to understand failure rates, and merely relying on LED lumen maintenance as a proxy for luminaire lifetime is inaccurate. Long LED lifetimes may not be realized at the luminaire level if, for example, the drivers fail prematurely or the lenses become cloudy. Clearly, developing a library of potential failure modes for LED luminaires, and not just the LEDs, is necessary to estimate the lifetime of these devices.