In a traditional lighting system, the lamp fails long before the ballast. In an LED lighting system, the driver may fail first. This has three ramifications of interest. First, care should be taken in specification of the LED product to ensure it has a high-quality driver likely to last. Second, if maximum longevity of the product is important, the product should allow easy replacement of the driver in the field. And third, care must be taken today to ensure the specific driver required by the product manufacturer will be available in the future.
Besides that, another potential failure mode is color. Color shift may occur in LED sources for various reasons, such as product design, ambient temperature or drive current. As with lumen depreciation, color shift is evaluated using the IES-LM-80 standard, which covers testing of change in color quality over time up to 6,000 hours. However, while TM-21 provides a procedure for extrapolating lumen depreciation to some point in the future, no similar procedure currently exists for doing so with color shift. In some spaces, the building owner may not consider this a major concern. In spaces where color appearance is important, however, visual inspection may determine that a product has failed and must be replaced.
The Next Generation Lighting Industry Alliance (NGLIA), an industry organization promoting solid-state lighting, recommends that life be based on the application, using manufacturer-estimated life as a guidepost. In one application, life might be determined as lumen depreciation (light levels) reaching a certain point. In another, when color shift or a portion of the LEDs (if visible to occupants) present objectionable aesthetics. In another, a combination of these.
In the end, the owner has a good idea but not absolute certainty when failure will be realized. As a result, it may pay to maintain a plan of stewardship of the lighting system to ensure it is operating correctly and evaluate its performance. This may involve a combination of visual inspection with spot-checking light levels. It could also be combined with standard maintenance best practices, such as luminaire cleaning (considering LED light output is directly related to useful life and especially in dirty environments), re-aiming of misaligned directional lamps and luminaires, and recalibration and reprogramming of controls.
Once a product has been determined to reach end of life, replacement is also influenced by what is actually being replaced. A majority of LED products are highly integrated devices. Some offer field-replaceable components, such as the driver. New components are typically limited to those offered or specifically recommended by the product manufacturer. The Zhaga Consortium, Piscataway, N.J., provides specifications for designing products that are open-source in terms of the light source and control gear, but the majority of products are not open-source.
Product Selection
One of the most effective things an owner can do to ensure the long-term performance of his or her LED lighting is to properly qualify the products prior to selection. During these early years of the LED revolution, product performance varies widely, and the lowest-cost option may not provide desired reliability. It’s not quite the Wild West anymore in LED history, but owners should take care.
This involves properly matching products to their operating environments, following manufacturer instructions, and ensuring the product warranty is sufficiently comprehensive and covers a reasonable portion of claimed life. The specifier might ask the manufacturer what data and methods they use to generate reliability claims. If color is a critical concern, the specifier might also ask the manufacturer how it ensures color stability and negotiate color as part of the warranty. Additionally, the specifier should inquire about the stock of replacement products and parts and how long that stock will be available.
More Information
LED lighting may reduce maintenance requirements, but, nonetheless, it can be beneficial to maintain these systems using traditional best-maintenance practices adapted to the unique characteristics of the LED source. This will help ensure the lighting system provides desired long-term performance for its users and thereby the greatest realized value. For more information, consult RP-36-15, IES Recommended Practice for Lighting Maintenance, written with assistance by me and published by the Illuminating Engineering Society, New York.