Stage lighting uses a variety of technical terms that often sound like something different from their meanings. Understanding these terms is important for aspiring designers, lighting technicians and other stage crew members. It is also important for performers and anyone else involved in the theatre to understand certain terms, such as "lighting boom," because it helps everyone communicate more efficiently about the performance.
A stage lighting boom is a vertical pipe that is placed on stage, usually to the side. Lights are hung on this pipe, so they can shine onto the stage from a horizontal angle. A broad base, known as a boom base, keeps the pipe stable. The base may be bolted to the floor in some instances, but more commonly it is weighted with sand bags or stage weights to counterbalance the weight of the lights hanging off one side.
Lighting performers from side positions provides an angle of light that creates highlights and shadows that make the subjects on stage appear more three-dimensional. Side lighting from booms is most frequently used in dance, where body shaping is crucial to the performance. They also may be used in theatrical performances to supplement light from other angles or create special effects that require low-angle side lighting.
On most proscenium stages--meaning stages where the audience is seated in front of the stage--lighting booms are placed on both sides of the stage, with a boom just upstage of (behind) each curtain that hangs down at the side of the stage. Six to 10 booms may be required to cover the full stage, and performers entering and exiting the stage next to these booms must be careful not to hit the lights.
Lights can be hung at any position along the boom's pipe, but the standard positions are known as shin (just off the floor), knee (about 3 feet off the floor) and head (about 6 to 8 feet off the floor). The lowest position is often called a "shin buster," as it is easy to knock your shins against the light when walking by, which is very painful.
Any performer standing in the wings must be careful not to have any body parts in front of the booms while waiting to enter the stage. Anything within the beam of the light will cast shadows onto the stage, potentially blocking light that is necessary for the performers or distracting the audience with moving shadows.