LED — maintained illuminance and the maintenance factor
The maintenance factor is fundamental to calculating the cost and the light parameters of any new lighting installation.
The maintenance factor, calculated from various data, gives the decline in the illuminance of a new lighting installation up to the first maintenance. The lighting designer determines this value, which then forms the basis of the maintenance schedule.
Guidance on determining the relevant values is given in CIE 97-2005.
The following are key to calculating the maintenance factor:
– the operating life and degradation of the LED
– the application (industrial or office)
– the type of luminaire (open or enclosed)
– the dust content of the air and the room maintenance factor
Different tasks and activities place different demands on lighting, which is why the European lighting standard EN 12464-1 specifies recommended illuminance levels. These are maintained illuminance values, and must therefore be observed as minimum requirements.
Both ageing and soiling reduce illuminance over time. To offset this effect — that is, to keep illuminance at the level required by the standard — the lighting installation must have a higher illuminance level when it is first installed.
The new value can be calculated with the following formula:
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