Maintenance factor

The maintenance factor serves as the basis for a lighting system’s maintenance schedule and depends on operating conditions, wear and tear, and the types of lamps used. This factor must then be determined by planners and operators, and the original value can be calculated as follows: Maintenance value = Original value × Maintenance factor. Specifying a maintenance factor prevents the illuminance from falling below the standardized level before the first maintenance.   Although maintenance values—such as illuminance—are standardized at the European level and must therefore not be undershot, the maintenance factors to be determined are not specified in any standard; consequently, the Technical Committee on Interior Lighting of the German Lighting Society (DLG), among others, has established guidelines. The recommended maintenance factors are therefore:

• 0.8 for cleanrooms or when usage time is low
• 0.67 for clean rooms and with a 3-year maintenance cycle
• 0.57 for outdoor lighting
• 0.5 for lighting exposed to heavy soiling

However, these maintenance factors are all very general and broad, which is why it is sometimes more cost-effective to determine a maintenance factor specific to each room. Various factors play a role here. First, the lamp replacement interval must be known in order to determine the maintenance factor for the lamp luminous flux due to lamp aging, as well as the lamp failure maintenance factor. Second, the luminaire cleaning interval is needed to determine the luminaire maintenance factor, as this affects soiling. Additionally, the room’s maintenance factor is important, since environmental soiling also plays a role. Ultimately, if many of these factors are known, it is recommended to use a room-specific maintenance factor; otherwise, one of the recommended values should be used.