The Second Generation

Over 4,000 hours of operation, the measured spectral power distributions (SPDs) and related color characteristics for the second-generation luminaires changed to a greater extent than expected. The high-temperature environment in Yuma may have caused, or at least contributed to, these effects, although luminaire design characteristics can also contribute to accelerated shifts in SPD.

The second-generation luminaires exhibited color-over-angle variability that produced noticeable color differences on the illuminated sand beneath the system. Determination of SPD and related color metrics at different angles is not currently included in standardized luminaire photometric testing. This type of variability may not be as noticeable in other applications, but the Yuma result demonstrates that as solid-state lighting (SSL) technology continues to evolve, the nature and the extent of the data that product developers, manufacturers, and specifiers need in order to evaluate the performance of products and systems are also changing. The development of relevant testing and reporting procedures and metrics of acceptability necessarily lags behind the identification of the need for certain types of data.

A Gap between Lab and Field Performance

The results from the Yuma GATEWAY evaluation highlight the gap that still exists between laboratory-based performance testing of LED lighting products and systems, and their performance in the field. While standard test methods such as LM-80, and defined calculation techniques such as TM-21 and TM-28, provide a critical part of the information needed for SSL, the results from this project show that system and field application conditions can make it difficult to predict installed performance over time. These predictions are likely more difficult in extreme conditions, such as those encountered in the Yuma evaluation.

While the initial energy, lighting quality, and maintenance benefits relative to the incumbent system were well documented and produced very satisfactory results for Customs and Border Protection, the evaluation raises questions regarding the long-term performance of LED lighting systems in high-temperature environments.  Ongoing improvement of current test methods and standards for LED luminaires, as well as new approaches to product and system development, are needed to improve performance of LED lighting systems.