The level of initial illuminance and thus the number of lamps and luminaires depend on the maintenance factor, which describes the decrease in illuminance over an installation’s period of operation due to lamp degradation and soiling of lamps, luminaires and the room. In educational facilities like general classrooms and training workshops, the actual expected maintenance interval and the type of maintenance must be estimated realistically and the maintenance factor must be selected accordingly. Under the conditions usually encountered in general-education classrooms, the reference maintenance factor of 0,80 should be specified in most cases. It is possible to arrive at other maintenance factors with individual determination based on object-specific data. In such cases, the conditions for the determination must be documented (see chapter “Maintenance factor”).
In cases of strong dust development, e.g. in workshops, or extreme maintenance conditions, e.g. in high rooms with impeded luminaire access (e.g. in high halls in vocational training facilities), longer maintenance intervals must be assumed. In such cases, a maintenance factor of up to 0,5 can be required to keep above the permissible minimum illuminance values (maintained values). Daylight-dependent regulation to a nominal illuminance reduces energy consumption, particularly at the start of a maintenance interval.