Castiglioni designed more than sixty lamps and a host of other objects, working from 1945 until 1968 with his brother Pier Giacomo and then on his own. One of their best-known lamp designs, Arco, came about through the challenge of a practical problem: how to provide a ceiling lamp that would not require drilling a hole in the ceiling.
Castiglioni's motto, "design demands observation," proved accurate, for it was a street lamp that gave the brothers the inspiration for this fixture. Street lamps, affixed to the ground, have a shape that enables them to project their light beams several feet away from their bases.
In this domestic adaptation, the Castiglionis were able to illuminate objects eight feet away from the lamp's base—far enough to light the middle of a dining table—by inserting a steel arch into a heavy Carrara marble pedestal. They studied the span of the arch to be sure that its form would provide enough space for one person carrying a tray to pass behind someone sitting at the table. In addition, they made sure the heavy lamp could be moved by two people by inserting a broomstick through the hole in the marble base. Arco is a prime example of the Castiglionis' rigorous approach to design solutions.
from The Museum of Modern Art, MoMA Highlights, New York: The Museum of Modern Art, revised 2004, originally published 1999, p. 296