Well-designed and properly operated LED lighting is generally reliable and long-lasting, while delivering solid maintenance benefits. But no lighting system lasts forever. Due to the characteristics of LED products, traditional maintenance practices have needed to evolve, as outlined in an update by the Illuminating Engineering Society to its standard RP-36-24, Lighting Maintenance.

The major consideration is lamp mortality. In other words, how do we know the light source has failed, and how do we replace it? With traditional lighting—fluorescent lighting, for example—this is generally simple: the lamp stops producing light. Maintenance personnel then replaces the lamp, called spot-relamping. In planned maintenance programs, all lamps in the system may be group-relamped after 5%–10% are spot-replaced, at which point it becomes economical to replace all the lamps at once. After that point, the failure rate will accelerate. Generally, the lamps will fail long before the ballast.

Inverting the status quo

With LEDs, this may be inverted; the driver may fail before the LEDs. This means LED products have a second major mortality mode, which is lumen depreciation. All light sources produce less light over time as they age. An LED product may eventually reach a point where it is emitting visible light but no longer providing minimum satisfactory light levels. While it has not reached the end of its life, it has realized its useful life and should be replaced.

LED product service life is typically rated based on this failure mode. While fluorescent lamp life, for example, was rated in hours as an average—the amount of time before one-half of a population of lamps would be expected to fail—LED products are rated with an L value, which is the number of hours before a certain level of lumen depreciation is realized. L70 is fairly common in nonresidential lighting, which is the number of hours before the product is projected to decline in light output by 30%. Other values include L50, L80 or L90. These ratings are based on at least 6,000 hours of source testing, with final rated life being a projection based on a standard method. 

Actual life, meanwhile, is highly dependent on operating conditions such as drive current and heat and luminaire features, such as the driver, thermal management and optics.

Besides lumen depreciation and sources failing to light, another mortality mode indicating end of useful LED product life is color shift, which is generally the result of the degradation of phosphors coating the LEDs. Typically, this will result in the light source appearing a bluish shade of white. There is currently no standard for predicting color shift beyond 6,000 hours or even determining what degree of it is acceptable, so this is a case of useful life being in the eyes of the beholder.

With LED products, spot relamping should be minimal aside from early failures, producing long mean times between relamping, which is the source of the old “install and forget it” mantra. Otherwise, group replacement should be considered when useful life is realized and may be considered a combination of maintenance and lighting upgrade. Because the failure mode may not be critical, this should ideally entail a practitioner periodically spot-checking light levels and visually inspecting the lighting system for burnouts, low light levels, color shifts and lighting control sequences of operation being out of alignment with space activities, flicker and misaligned accent lighting.

Service and maintenance shifts

This is a significant needed shift in maintenance—from reacting to problems as they come up to stewardship or scheduled inspections of the lighting system to ensure it is doing its job. Inspection includes troubleshooting, repairs and, in some cases, cleaning. On the latter point, many LED luminaires feature a sealed optical cavity, which prevents dirt and dust—and bugs, in the case of outdoor units—from entering. However, because lumen depreciation can reach high levels at end of life, and useful life is based on lumen depreciation, luminaire cleaning can play a significant role in getting the most out of the lighting system.

Now we get to servicing. While group relamping of traditional luminaires and LED lamps is somewhat straightforward, doing it with LED luminaires is not. The luminaire may be highly integrated with no intention for it to be serviced, require major disassembly for servicing or be fully serviceable in whole or part “below the ceiling.” In the last case, the luminaire may require proprietary replacements from the original manufacturer or be open-sourced—that is, based on a common specification such as Zhaga.

LED lighting systems are relatively close to, but not quite, maintenance-free. The maintenance practices are familiar, but they must be adapted to the special characteristics of this light source, which is now predominant. Electrical contractors interested in this topic can learn more by getting IES-RP-36-24 at the IES store here.

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