How electric light created new spaces that transformed the built environment and the perception of modern architecture. In this book, Sandy Isenstadt examines electric light as a form of architecture--as a new, uniquely modern kind of building material. Electric light was more than just a novel way of brightening a room or illuminating a streetscape; it brought with it new ways of perceiving and experiencing space itself. If modernity can be characterized by rapid, incessant change, and modernism as the creative response to such change, Isenstadt argues, then electricity--instantaneous, malleable, ubiquitous, evanescent--is modernity's medium. Isenstadt shows how the introduction of electric lighting at the end of the nineteenth century created new architectural spaces that altered and sometimes eclipsed previously existing spaces. He constructs an architectural history of these new spaces through five examples, ranging from the tangible miracle of the light switch to the immaterial and borderless gloom of the wartime blackout. He describes what it means when an ordinary person can play God by flipping a switch; when the roving cone of automobile headlights places driver and passenger at the vertex of a luminous cavity; when lighting in factories is seen to enhance productivity; when Times Square became an emblem of illuminated commercial speech; and when the absence of electric light in a blackout produced a new type of space. In this book, the first sustained examination of the spatial effects of electric lighting, Isenstadt reconceives modernism in architecture to account for the new perceptual conditions and visual habits that followed widespread electrification.