“Install it and forget it” is no way to maintain an LED system, writes Norma Frank in her October “Maintenance” column in LD+A. Indeed, early sales claims by some that LED products are install-and-forget devices have been proven false. The same best practice that determines selection of conventional products for reliability and easy maintenance applies to LED products. While end users will not maintain LED installations exactly the same way as their conventional lighting installations, they will need to maintain them in order to preserve design integrity and performance while maximizing longevity. Some tips for success:
1. Specifiers should ask questions.
The LED luminaire market is stratifying similar to conventional lighting, with standard- and specification-grade tiers. Products designed for each will offer different levels of performance.
Qualifying the reliability of these products requires a high degree of diligence. Specifiers need to ask manufacturers what methods and data they used to produce their reliability and service life claims. As industry-consensus methods of determining reliability develop, they should require manufacturers to follow them.
For applications where color quality is important, they should also ask manufacturers about how they ensure color stability. As there is no industry standard for this, predicting color stability (shift) is difficult.
2. Specifiers should understand the product warranty.
Specifically, what it covers and what it doesn’t. Does the warranty cover color stability? (It usually doesn’t, so for color-critical applications, this would need to be negotiated.) Does the warranty period cover a reasonable portion of claimed life? In today’s era of short product cycles, will the manufacturer maintain a stock of replacement products and parts, and if so, for how long?
3. Specifiers should understand what “fail” means.
Assuming proper installation of a quality product whose reliability is well understood and matched to the application, the end-user must now maintain it. Most important, of course, is operating the product within its parameters. Even so, over time, products or components will fail. But what does “fail” mean?
The lighting industry predominately uses lumen depreciation to express an LED product’s expected life. A published L70 value of 50,000 hours, for example, indicates average light output for a population of products is expected to fall by 30 percent after approximately 50,000 hours of operation. This lumen depreciation may occur due to general lumen depreciation among lit LEDs, a percentage of the LEDs outright failing, or depreciation within the luminaire.
Because LEDs keep improving and provide very long life, and because each LED product is a purpose-built lighting device, life expectations are based largely on manufacturer experience and methodologies. The IES-LM-80 standard covers lumen depreciation testing for LED packages, modules and arrays up to 10,000 hours. IES-TM-21 provides a procedure for extrapolating this information to L70 or some other target. Because luminaire design can have a big effect on light output, IES-LM-80 data provides a baseline for estimating lumen depreciation for LED products under certain conditions. Not only does luminaire design impact life, but environmental stress factors as well, such as heat and humidity in the field. The result is manufacturers estimate expected life based on their own methods and data.
In short, end-users should not mistake the L70, 80, etc. number with an exact point at which replacement is recommended. Additionally, lumen depreciation is just one indicator of life. LED products are not sources, but systems of components. Research conducted by RTI International, summarized in the 2013 report, Hammer Testing Findings for Solid-State Lighting Luminaires, suggests components other than the source, such as the driver electronics, are more likely to fail first. Additionally, color is another potential failure mode. This is both an issue of color stability for a product, and color consistency between products in the same space, over time.
AN APPLICATION APPROACH
The Next Generation Industry Alliance’s (NGIL) LED System Reliability Consortium (LSRC) offers some recommendations for end-users. The organization recently updated their report, LED Luminaire Lifetime: Recommendations for Testing and Reporting, available at the DOE SSL program website. LSRC recommends that life be based on the application. This would entail valuing life on an application basis and using manufacturer-estimated life as a guide for selection of appropriate products. For one application, it might be when average light output has declined by X percent based on local light level needs. For an application where color quality is important, it might be when average light output has declined by X percent and color shift has exceeded a specified limit of Y. If occupants have a direct view of the LEDs, the overall failure mode may include when Z percentage of the LEDs fail (go dark). In other applications, service life may be a list or combination of X, Y and Z thresholds. This method sensibly combines functional and aesthetic failure based on application needs.
Because the timing of these failure modes is uncertain, and “failure” may be defined differently for different spaces in an installation, the end-user must be a good steward of their lighting system. In fact, with LED installations, it’s arguable that maintenance best practices and a written maintenance plan are even more important than they are with conventional lighting. The end-user should visually inspect the lighting system and spot-check light levels on a periodic basis to monitor whether the system has reached the end of its useful life. Because light levels will typically be a key factor, luminaires should be periodically cleaned to maximize the useful life of the system. Additional components of the maintenance plan should also include re-aiming luminaires, re-calibrating controls, etc.
LED lighting offers numerous benefits, but those benefits only last as long as the product’s performance. Planned maintenance is key to realizing those benefits for as long as possible. A critical component of this maintenance is monitoring to ensure that the system is always delivering desired performance and aesthetics.