How can contemporary light art installations impact the sensorial perception of the urban context to modify and reinterpret urban space? In Robert Irwin's words, how can they provide "...an extended way of looking at the world"? In this paper, we examine how temporary light installations may impact the public realm by modifying citizens' perceptions of moments in the city: a habitual urban passage is interrupted with a temporal experience, changing the way the urban space is experienced. We explore how site-specific light installations create unique intersections of audience and spatial perception through the artists' intent of creating new urban atmospheres through an experiential layer added onto the urban fabric during light festivals. To do so we analyze and discuss two light installations that we designed and executed, which were shortlisted for the 2022 [d]arc awards. Both projects took part in larger urban light festivals and were located within urban passages. "Reflecting on Troy"[Author 1 - Troy Glow Light Festival] created a temporal light graffiti in an urban alley, while "Riddle 102"[Authors 2,3 - Nobel Week Lights], a dynamic lighting installation in a 231m pedestrian tunnel, created an immersive environment that alters the perception of the tunnel's physical dimensions. Through reflections, as well as visitor and curator reviews, we unpack the intent and impact of the works on the perception of the urban context. We discuss and analyze the similarities and differences between the two urban settings, identify the design processes and principles pertinent to site-specific light installations [materials, lighting fixtures, testing] and address the impact darkness and over-lit spaces have over spatial perception. Lastly we discuss the impact a temporary light installation may have on the collective memory of the city, perceived in person or online.