How does light transform the objects it shines upon? What are the consequences of such meta- morphoses on architectural thought? Book of Hours seeks to answer these questions. To this end, it presents the architect Frida Escobedo's research on the transformative effect of light on matter. Time lapses show the process in action and translucent paper mimics the permeable barrier between light sources and objects and enacts the mutability of matter. 50 Illustrations, unspecified