More than seven billion people were exposed to days of dangerous heat last year, and heat-related deaths now number close to half a million annually worldwide. Urban heat islands, where asphalt and concrete absorb and radiate warmth, make city life increasingly unbearable. While the sun is above the horizon, little can be done. But once it sets, temperatures drop by radiant cooling – and that window of relief is precisely what Leni wants to design around, to accommodate all people who experience night.

Her paper identifies five features of a failing nocturnal city: fear that keeps people indoors resulting in loneliness, environmental harm from excessive light which disrupts ecosystems, overbearing surveillance technologies, a lack of meaningful public participation in urban design, and the absence of any coordinated nighttime governance. The consequences play out in pedestrian fatalities, poorer health outcomes for night-shift workers, and a deepening sense of urban isolation.

The antidote, as Leni sees it, is something she calls Noctopia: a liveable, welcoming, community-shaped night city, which can be enjoyed during hot weather and long winter nights alike.

Picture streets where luminous benches offer safe rest stops and softly lit intersections guide pedestrians home. The library stays open at midnight. A night market hums along the transit corridor. Down the road, an open-air concert is underway in the local park, with audio headsets available so the music doesn’t bleed into the surrounding neighbourhood. Historic façades are radiant in the distance, providing pedestrians with streets that have ‘luminous legibility’ – Leni’s term for the ability to read and navigate a place through light.

Central to realising this vision is adaptive LED lighting – technology that dims, shifts colour, and responds to who is using a space, when and where, setting the mood much as a theatrical lighting designer would for a stage production. Crossfades between brightness levels can signal the shift from active evening hours to quieter late-night calm.

But technology alone isn’t enough. Leni is insistent that the communities who live and work at night – shift workers, musicians and artists, elderly residents, families, people with disabilities – must shape the spaces built for them, through genuine participatory design rather than token consultations or online polls.

Night, she reminds us, has always been cooler than the day. Cities just haven’t learned to design it yet.