What you should know about lighting system maintenance (1)


Facility owners view lighting maintenance as an absolutely necessary evil-i.e. expense-to help sustain the full economic value of their system. Facility managers and lighting-maintenance contractors sustain the full value of their time through lighting maintenance.


As soon as a new lighting system is energized, the light level starts to gradually decrease because of various aging characteristics. For that reason, a lighting design usually provides, initially, an illuminance (a footcandle level) above the minimum-specified level to compensate for the light reduction over time.

Light depreciation is defined by the term light loss factor (LLF). Expressed as a percentage, the LLF considers all the conditions contributing to the reduction of light over time. In addition to the gradual and constant reduction in a lamp's lumen output, a percentage of gradual light reduction also comes from the dirt buildup on the reflecting surfaces of a luminaire and on the surfaces of a room. The LLF should always be included in any calculations to determine the lighting requirements in a space.

Maintenance reduces lighting costs The initial foot-candle level of a lighting system decreases over time because of depreciation. For that reason, a well-thought-out program of regular maintenance can greatly reduce these light losses and pay for itself by saving on energy costs.

In a new installation, rather than having excessive initial illumination to allow for a 0.70 LLF, regular washing and group relamping is recommended. Such an approach changes the LLF to 0.95 (a 5% loss), thereby permitting the lighting system to use 25% fewer lamps and luminaires. This reduces electric energy use by 25%. Additional savings come from reduced air-conditioning loads and smaller electrical system components, such as transformers, panelboards, and feeder conductors.

The key to getting the greatest benefit from group relamping is to select the best time interval between relamping. While it is impossible to predict when each lamp in a lighting system will fail, a certain number of lamps will fail in a predictable manner. This is shown in the lamp's morality curve supplied by the lamp manufacturer.

Thus, group relamping follows the lamp's morality curve. Two systems can then be used to apply the morality curve.

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