To ensure that the required illuminance is provided over a period of time, the lighting design includes a maintenance factor MF that takes into account the reduction of luminous flux. The new value for the illuminance of an installation is calculated from the maintained value of illuminance, and the maintenance factor. The maintenance plan specifies the cleaning frequency of the luminaires and the room and the lamp replacement. The maintained value of illuminance thus depends on the luminaires, the lamps and the room conditions.
Luminaire Maintenance Factor
The luminaire maintenance factor LMF takes into account the reduction of luminous flux due to the soiling of the luminaire. It signifies the ratio of a luminaire’s light output ratios before and after cleaning. The LMF depends on the version of the luminaire and the related possibility of soiling. The LMF classification is indicated next to the product. At this point, the optimal cleaning frequency must be defined for the maintenance plan.
Room Surface Maintenance Factor
The room surface maintenance factor RSMF takes into account the reduction of luminous flux due to the soiling of the room surfaces. It signifies the ratio of the room surface reflectances before and after cleaning. The RSMF depends on the degree of soiling of the room or the ambient conditions of a room and the specified cleaning frequency. Further influencing factors are the size of the room and the type of lighting (direct to indirect emission).
The room surface maintenance factor consists of four classifications for room surface deterioration: P pure (very clean room), C clean (clean room), N normal (average conditions) and D dirty (dirty room).
Lamp Lumen Maintenance Factor
The lamp lumen maintenance factor LLMF takes into account the reduction of luminous flux due to the ageing of the lamp. It signifies the ratio of the lamp lumens at a specific time and the new value. The current data provided by the lamp manufacturers must be taken into account here.
Lamp Survival Factor
The lamp survival factor LSF takes into account the variation of the life of individual lamps from the mean life of the lamps. The LSF depends on the service life of the lamp. The latest data provided by the lamp manufacturers must be taken into account here. If defective lamps are replaced immediately, the lamp survival factor applied is LSF = 1. The maintenance plan for a lighting installation must also specify the optimal lamp replacement frequency. This depends on the degree of use of the lamp and is determined by analysing the period of illumination and the mean service life of the specific lamps.