LED area and roadway lighting promises energy and maintenance cost savings, but the longevity of the LED light source presents a hitch. Traditionally, luminaires are cleaned upon relamping. If relamping does not occur, dirt buildup becomes a more important maintenance factor. That being said, it is claimed LED luminaires are less prone to dirt accumulation. So what’s an appropriate cleaning interval?

In 2016, the Illuminating Engineering Society published an important maintenance study conducted by the Virginia Tech Transportation Institute as IES-RES-1-16. Specifically, VTTI looked at luminaire dirt depreciation (LDD) in LED roadway luminaires, impact on light distribution and the efficacy of different cleaning methods.

The study evaluated the impact on dirt and various cleaning methods on a range of luminaire types in both in a laboratory and in the field. While insufficient sampling did not yield new LDD curves, the authors were able to recommend a linear LDD rate for consideration. Key findings:

* LDD is different for LED luminaires and can be significant at end of life
* An alcohol solution or mild detergent solution can be safely applied to many luminaires and is more effective at mitigating LDD during cleaning than dry wipe or plain water
* Minimum potential LDD and change in lighting uniformity rates are +1 percent per year LDD and +1 percent per year uniformity change for luminaires with flat glass luminaire optics, and +3 percent per year LDD and no uniformity change for luminaires with no luminaire optics.

These findings and plenty more can be found in the study, which is available free for download here.