Balancing Luminance and Illuminance Concepts in Urban Lighting

In road lighting, concepts of luminance are applied for motorised traffic in an adequate way to describe visibility of objects and fulfilling all aspects of the seeing task. Sometimes this is expressed by means of the so-called Visibility Level-VL in terms of the visibility of (small) targets - STV (of reference targets).
In residential areas and areas with slow moving observers however, and in environments with a complex background, working with luminances is sometimes becoming impractical.
Moreover, recognition of persons and their intentions can be described in terms of the semi-cylindrical illuminance as there is existing a correlation between the luminance of the faces and the value of the semi-cylindrical illuminance.
Therefore, a research project has been set up to study the applicability of horizontal, vertical, semi-cylindrical, hemispherical, spherical cap illuminances, as well as cubic illumination in practical outdoor applications (urban and other exteriors).
These concepts are being weighed against luminance concepts to qualify and quantify a number of criteria within urban lighting.
These criteria are for instance : general visibility and specific detection of obstacles, conspicuity, visual orientation, recognition of persons, modelling of three-dimensional objects; ...
Particular elements of public spaces are chosen to be worked out in detail such as a road, a footpath, a cycle track, a park, a river and a riverbank. These are then treated as a typology in solving other cases.
Photometric measurements of illuminances and luminances are carried out to characterise the outdoor visual climate.
RELUX simulation and visualisation software has been used to figure out the lighttechnical parameters; also the software package ULYSSE (Schréder) has been run.
An equilibrum and balance has been found in characterising the seeing task in terms of different types of illuminance and of luminances; and even aspects of light pollution, energy consumption together with the creation of an attractive visual scenery have been considered.