The lighting quantity recommendations set out in European lighting standards such as DIN EN 12464-1, e.g. for levels of illuminance, refer to values that need to be maintained. This means that the lighting quantities in question must never fall below them. However, because lamps, luminaires and room surfaces 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.
Maintenance factors depend on operating conditions as well as on the type of lamps, electrical gear and luminaires used. They need to be defined and recorded by designers (and operators) and form the basis of maintenance schedules. Values required on installation are calculated as follows: value on installation = maintained value / maintenance factor.
All values set out in European lighting standards such as DIN EN 12464-1 – e.g. for levels of illuminance – are minimum values that need to be maintained at all times. This means that the lighting quantities in question must never fall below them. Hence the need for higher initial values (values on installation). If only maintained values were realised on installation, a new lighting system would immediately require maintenance. The values required on installation are determined by applying a maintenance factor.
In the context of exterior lighting, the term mounting height means the height from which light falls on an illuminated surface.