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In exterior and interior lighting, the components of illumination quality are determined by visual performance, visual comfort and the visual atmosphere. Here, visual performance comprises the level of illumination and the limitation of glare. Visual comfort determines colour rendering and a harmonious distribution of brightness. The visual atmosphere deals with light colour and light direction.
Visual performance is determined by the level of illumination. It is influenced by the degree of illuminance and the reflection properties of an illuminated surface. Here, the following applies: The lower the reflection, the higher the degree of illuminance must be. A white wall has a reflection degree of up to 85%, while a red brick facade only has up to 25%. To compensate for low visual performance, the degree of illuminance must be raised.
Maintained illuminance defines the average degree of illuminance on a reference surface. In the course of the working life of a lighting system, ageing and environmental influences change lamps, luminaires and spaces. The degree of illuminance diminishes. This reduction is described by maintained illuminance. To compensate, new systems should have higher illumination values.Maintained illuminance = maintenance factor x value as new.
The maintenance factor is dependent on the type of lamp, the luminaires, the dirt in the environment and the maintenance intervals. In a clean environment, for example in an office, and with a maintenance cycle of three years, a value of 0.67 can be calculated, and in a dirty room situation 0.5. The surface on which the degree of illuminance is to be implemented is used as a calculation basis. In office workstations, the measurement is taken at a height of 0.75 m above the floor, in traffic areas at a maximum height of 0.1 m.
The required maintained illuminance for the degree of illuminance is defined in the standard DIN EN 12464-1 for indoor work places for various types of rooms and activities and in DIN EN 12464-2 for outdoor work places.