On-site inspections, an analysis of the qualitative and quantitative formal values and an examination of the town's problems led to the conclusion that the historic centre of Siena was to be considered as a single monument and that its lighting system should not undergo major changes. Rationalizing, unifying and technologically updating the already present fixtures and light sources immediately produced significant results in terms of urban planning and viewing comfort, without altering the existing wiring. Thus, the ever-present wrought-iron lanterns were maintained, while the existing light sources were replaced with the latest metal halide bulbs with ceramic burners. Luminance values were raised and color temperatures were combined with higher color rendition to give a sense of continuity and order to the urban fabric. Old and obsolete fixtures were replaced with custom-made double “Radius” fixtures by iGuzzini. The emission of 120º blades of light with symmetrical optics cut-off towards the roadway and a special diffuser shield, directed towards the top part of the façade opposite, light up the streets and buildings with diffused, constant lighting. Good luminance levels have been achieved both on the horizontal and vertical planes without glare, ensuring pleasant viewing. Furthermore, the lighting fixtures have no visual impact either during the day or at night.