In the film industry, the term "gobo" is used to refer to a "go-between," or an object that falls between the lighting source and the object to be filmed. Gobos create special effects with the light, including specific colors and shapes. Gobos aren't just used in the film industry, either. You may have seen people using spotlights with commercially produced gobos to cast light effects on the outside of their homes and businesses during holidays or special events.
In film noir, the shape of the shadows, both on the subject and across the background, help set up the scene. For example, shadows of prison bars can evoke the mental image a dark jail cell. Those shadows are an important part of the setting, and they can add to the artistry of each scene.
The great thing about gobos is that they never actually appear in frame. They don't need to. Our minds combine the dialog and body language from the actors with what we can see on the set to create an assumption about what's behind the camera. Thus, you don't need prison bars to create that effect of being behind bars. Instead, you just need a gobo that can create shadows that look like prison bars.
Since gobos never appear in frame, you could create your own instead of purchasing an expensive gobo device. Cardboard and poster board make good gobo templates. Just cut out the shape of the light you want to cast, then position the gobo between the light and the framed shot as needed to create the desired effect. Also, consider using objects around your house as gobos, like an oscillating fan or window blinds.
That concludes our tips, but be sure to check out even more great information about film noir photography on the next page.