*1.2. The Challenge: A Sustainable Street Lighting System for the City of Rotterdam*

This paper presents the results of a practical case of eco-efficient value creation. It is the design of a street lighting system for a typical city in Western Europe: the city of Rotterdam.

Public street lighting has a major influence on safety [14,15], the perception of safety, and in general the atmosphere in the street. The municipality of Rotterdam has the desire to create a pleasant atmosphere in the city during both day and night by street lighting systems. An additional aspect of well-being in cities is the local presence of nature, i.e., trees [16,17]. So lighting and trees are both important aspects of the value for the citizens. However, in the conventional design of street lighting systems, there is a conflict below the ground: the roots of the trees interfere with the power cables, see Figure 1. This conflict causes difficulties during installation, maintenance and operation as well as end-of-life, which all lead to higher costs for the application of street lighting systems.

The underground conflict between tree roots and power cables can be solved in two different ways: (1) find other ways to create residential green, e.g., with plant boxes; or (2) redesign public street lighting. Within the first direction many solutions can be found, however, that is not the scope of this paper. To find acceptable solutions for the second direction is not easy. Since 1800, the lamppost has looked the same: a light source on a pole. Other forms such as hanging street lighting with hanging power cables above the ground are generally not regarded as desirable.

From the point of view of sustainability, the system requirement is obvious: the design must combine LED lighting with local PV cells as the source for the required electricity. Replacing the classic lamps by LED lamps is easy. Where to place the PV cells is less easy: (1) PV cells above the street will require expensive construction; (2) PV cells on the roof are a logical choice, but why would the owner of the building allow the municipality to attach the PV cells?

**Figure 1.** Conflict between residential street lighting systems and trees: the power cables are entangled in the roots.

The design of a new street lighting system has to fulfil three value aspects for the 3 stakeholders: (1) the requirement of streetlights in combination with trees, which is the value for the citizens; (2) it must be affordable (not too expensive) for the municipality; (3) it must resolve the issue "what is in it for me?" for the house owner with regard to the PV cells. At the same time, the new system must have a (much) lower eco-burden score in LCA compared to the classical system of Figure 1.
