ABSTRACT
After selecting the design value for the ambient illumination, the lighting designer decides upon the illumination hierarchy, which determines the distribution of illumination within the space. This is achieved by providing direct illumination selectively onto specific surfaces and objects. An illumination hierarchy expresses a lighting designer's concept for the overall appearance of a lit space. It specifies the ambient illumination level as a mean room surface exitance (MRSE) value, and it expresses how the distribution of direct flux from the luminaires affect the relative appearances of specified targets in terms of a distribution of target/ambient illuminance ratios (TAIR) values. The principal means for assessing the performance of a daylighting installation has for many years been the daylight factor. Despite a fair amount of recent activity aimed at improving the modelling of outdoor daylight availability, the daylight factor continues to be concerned with provision of illumination onto indoor horizontal working planes (HWPs).
