1342Maintaining System Performance

As with most manufactured products, lighting systems lose performance over time. This degradation can be the result of Lamp Lumen Depreciation (LLD), Fixture Dirt Depreciation (LDD), Room Surface Dirt Depreciation (RSDD), and many other factors. Several of these factors can be recovered to maintain performance of the lighting system. Figure 13.5 shows the LLD for various types of lighting systems

Lamp Lumen Depreciation occurs because as the lamp ages, its performance degrades. LLD can be accelerated if the lamp is operated in harsh environments, or the system is subjected to conditions for which it was not designed. For example, if a fluorescent system is turned ON and OFF every minute, the lamps and ballasts will not last as long. Light loss due to lamp lumen depreciation can be recovered by re-lamping the fixture.

Fixture Dirt Depreciation and Room Surface Dirt Depreciation block light and can reduce light levels. However, these factors can be minimized by cleaning surfaces and minimizing dust. The magnitude of these factors is dependent on each room, thus recommended cleaning intervals can vary. Generally it is most economical to clean fixtures when re-lamping.

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