Here’s a good example of Gordon Willis’ use of the bay light.
This unit had been around the industry in a variety of configurations and names (‘coop’ lights, soft boxes, etc) for decades until he saved it from obscurity during the shooting of The Godfather in 1971. Find this scene at the 0:32:06 mark…
Mounted directly above the set, it produces an effect that’s soft and flat. Connected to a dimmer board, it’s generally used to provide a base illumination to whatever space you’re working in. Absent any foreground fill light however, it tends to create deep shadows in the actor’s eye sockets. You’ll recognize the effect as it’s so masterfully applied by Willis to the face of Marlon Brando’s Don Corleone in the opening of The Godfather.
Construction of a bay light is simple and cheap. A series of high-wattage household bulbs are secured to a batten within a light-weight wooden frame. The bulbs fire upward into white reflective material which then bounces the light downward through a sheet of semi-transparent diffusion, such as Lee 216. Duvetyne curtains line the sides of the box and can be easily dropped to any height to control the spill. Bay lights are usually built in 4’x4′ or 4’x8′ sizes, though any dimension is easily attainable.
Note that in this scene Willis augments the bay light with harder sources in order to create some contrast and fill. He also uses specific window treatments – Hamburg Frost and a layer of white bobbinet – to help throw the backing further out of focus.
Note the shadows falling on the set wall behind Shelley Long and Tom Hanks. They give away the foreground fill source that augments the bay light from above.