Maintenance factors form the basis of all lighting installation maintenance schedules. They depend on operating conditions as well as on the type of lamps, electrical equipment and luminaires used. Maintenance factors need to be defined and recorded by designers (and operators). Values required on installation are calculated as follows: value on installation = maintained value / maintenance factor.

The lighting variable recommendations set out in European lighting standards such as DIN EN 12464-1, e.g. for levels of illuminance, refer to maintained values. These are values below which the lighting variables in question must never fall. However, because lamps, luminaires, walls and ceilings are subject to ageing and soiling, the values that are registered when lighting is new decline as operating time increases. So, to enable a lighting system to be operated longer without additional maintenance work, values on installation need to be correspondingly higher. How much higher is determined by maintenance factors.