Le Corbusier called it “the masterly, correct, and magnificent play of masses brought together in light.” Louis Kahn spoke of spaces where “the structure of the building gives rise to the structure of the light.” For the greatest architects of the modern era, the management of natural illumination was not a technical afterthought but the primary medium of their art — the material they worked in as surely as stone or steel, and the one that gave every other material its character and presence.

The Pantheon in Rome, built in the second century, remains among the most instructive demonstrations of what light can do when it becomes the subject of a building rather than merely its illumination. The single oculus at the dome’s apex casts a moving column of light that traces the floor slowly across the hours of the day — a clock, a meditation on time, and a spatial drama that contemporary architects have spent two thousand years attempting to match. Those who have come closest share a commitment to the slow study of how light moves through a specific place at a specific latitude: where it enters in winter, where it pools in the afternoon of a summer solstice, how it diffuses through a stone wall or sharpens through a metal grille.

The return of daylight as a primary design consideration in contemporary architecture — after decades in which mechanical lighting allowed designers to treat windows as optional — reflects a growing body of evidence about the biological importance of natural light to human health, mood, and cognitive performance. The well-designed room is not merely beautiful. It keeps better time.