May there be light : A study of optimising public lighting in park spaces for energy efficiency and subjective factors

Abstract: Public lighting is an important part of city infrastructure. In parks, it enables activity, transportation and recreation in the darker hours. As the field of city lighting is rapidly expanding and advancing, innovations like customisable luminaries and LED light source options are making their way into the fray. This study is focused on comparing two parks with different lighting setups: Tegnérparken – equipped with newer, individually programmable luminaries with LED light sources and a separate control system (Interact City), and Bergsbrunnaparken – which hosts non-customisable luminaries with halogen light bulbs. By interviewing relevant professionals, conducting a survey, and performing several field studies in the two parks, many subjective factors were identified. These are the unmeasurable entities that lighting affect – like sense of safety, comfort, light pollution and blinding.  In order to create a more energy efficient system that does not compromise with the subjective factors, but rather improves them – a new schedule with changed dimming levels is designed for Tegnérparken. By simulating the schedule in Python, the new schedule shows a 15 percent reduction in energy consumption compared to the old. Compared with Bergsbrunnaparken, the improvement is between 46 (old schedule) and 54 (new schedule) percent.  The study also point to a range of possible improvements in Bergsbrunnaparken, that should be taken into account when thinking of redesigning the lighting there. These are based on input from investigating subjective factors, as well as lux measurements and visual inspections.  The study resulted in a change of schedules in Tegnérparken, as the new one was accepted and implemented by Uppsala Kommun in late May 2021. It is also groundwork for further studies into implementing the Interact City system throughout more park spaces, and its usability for improving subjective factors with relative ease.  The study is commissioned by Uppsala Kommun.