Light It And Forget About It?

In any lighting system, lamps and auxiliary electrical devices fail and must be replaced. Dirt and dust accumulates on fixture surfaces and should be cleaned. System problems must be corrected, and lighting controls should be adjusted as space conditions change.

In short, all lighting systems degrade over time and must be maintained—even light-emitting diode (LED) luminaires, which are sometimes described as maintenance-free devices. Growing LED lighting adoption, however, will require owners to adapt their maintenance practices to this new source.

Consider lamp replacement. In a typical conventional fixture, lamp or ballast failure is clearly indicated by the lamp failing to light. Maintenance personnel then replace the lamp, a practice called spot relamping. In planned maintenance programs, all lamps in the system may be group relamped after 5–10 percent have failed (fluorescent) or otherwise when they reach end of useful life, which may be defined as when a certain level of lumen depreciation in the fixture is realized (LED). With LED lighting, life ratings are typically based on L50, L70, L80, L90, etc. An L70 of 50,000 hours, for example, means the product is expected to produce 70 percent of its original light output after 50,000 hours of operation.

The question, then, is how the owner knows when an LED product’s useful life has expired and when it is time to replace it. At 50,000 hours, the luminaire will be operating, unless the driver failed. Will the owner even remember to replace their lights after 13 years? Even the 50,000-hour number is only an estimate; actual life may be influenced by a number of design and environmental factors, such as ambient heat and product design. This can be particularly problematic when minimum light levels are critical for productivity or required by code. Of course, again, the point is moot if the driver fails around or before the light source gives out.

One solution is to build some type of indicator into the fixture or control system that tells the owner it is time to relamp based on rated life having been consumed. But, again, the product may “fail” long after that, depending on the product and its application. Another solution is to automate some form of feedback, such as through installation of a light sensor. But the cost of such a device, coupled with the labor involved in calibrating it to the application, would be burdensome. Yet another solution is to set up a regime of spot-checking light levels each year, noting the effect of space changes that may affect reflectances or task changes that may alter light level requirements.

Another promising idea is to embed a controller in the fixture that maintains a constant light output over the product’s life, underdriving the fixture for most of its life until the end, when it will begin overdriving, causing light output to plummet and providing a clear end-of-life signal.

When it is time to replace the LED lights, group relamping will make the most sense, as LEDs tend to depreciate at the same rate, meaning all of the fixtures in the same space will likely require replacement at the same time. On the plus side, unless drivers begin failing prior to group replacement, few or no spot replacements are expected—i.e., there’s a very long mean time between failures—which is a good maintenance benefit.

When the LED lights must be replaced, what is actually replaced will depend on the type of LED fixture. Many luminaires are highly integrated, and the light source and driver either cannot be replaced or can only be replaced with major disassembly. This will present a significant cost to the owner in the future but ideally would coincide with the building’s remodeling cycle. Some new products are modularizing the light engine, heat sink and driver to allow convenient upgrade or maintenance. The Zhaga specification is now seeking to standardize the interface between the fixture and its components. (For more on Zhaga, see “LEDs’ New Standard” on page 86.)

While LED fixtures are expected to operate for many years without spot replacement, they should be cleaned periodically, including wiping lenses and removing debris that could interfere with the luminaire’s thermal design. Many LED fixtures have a sealed optical cavity, which prevents 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 in fact based on lumen depreciation, fixture cleaning can be an important part of maintaining the integrity of the lighting system.

Finally, accent lights frequently fall out of alignment with merchandise, art or other focal points requiring highlight. As a result, LED accent lights should be inspected periodically to ensure they are correctly aimed. The same with control recalibration. Meanwhile, advanced control systems can provide remote detection of outages and other potential maintenance issues.

LED lighting systems are close to, but not quite, maintenance-free. The maintenance practices are familiar but must be adapted to the special characteristics of this new light source.

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