This is a term that used to be used in national lighting standards. It was defined as average illuminance in a fully furnished room in relation to the average ageing condition of the lighting installation. To establish the illuminance required on installation (initial illuminance), nominal illuminance was multiplied by a planning factor of 1.25.
Today, the decline in illuminance due to ageing and soiling of lamps, luminaires and room surfaces is taken into account by applying a maintenance factor. The illuminance values indicated in DIN EN standards are maintained values.