The maintenance factor used to determine initial illuminance depends on local soiling conditions in industrial work places. In addition to the influencing factors on the decrease in illuminance over the period of operation, maintenance factor and thus initial illuminance must consider the maintenance interval and consequently maintenance costs. Initial illuminance in areas with access difficulties e.g. above crane runways or at great heights will usually be higher to achieve a longer maintenance interval and thus reduced maintenance costs. Fundamentally, lighting installations should be maintained regularly.
Often, operating conditions as well as maintenance method and schedule are not sufficiently known at the time of design, which renders a specific determination of the maintenance factor impossible. In such cases, reference factors for lighting design are 0,67 for clean rooms, 0,57 for normal rooms and 0,50 for soiled rooms (see also chapter "Preservation of the lighting level (maintenance factor)").
In the food and luxury foods industry, room hygiene requirements are mostly very high, which means in such cases the criteria “very clean rooms” apply for determining the maintenance factor. Where they are adhered to and state-of-the-art lamp and luminaire technology, high protection ratings etc. are utilised, a maintenance factor of 0,8 can be applied (see also chapter "Maintenance factor, LED luminaire example").