The first concern of all theater lighting is illumination. This includes the stage lights that allow the audience to see the actors and scenery as well as the general lighting that allows the audience members to find their seats and read their programs before and after the show and during intermission. The basic lighting that fulfills this purpose on the stage is known as face lighting, as it is designed to present a clear view of the performers' faces. The lighting over the audience is called house lighting.
Lighting is also used to create dimension and distance, sometimes referred to as "shaping." This is only used on the stage and is characterized by lighting aimed at the stage and performers from the side and back. The shadows cast by side lighting serve to highlight the dimensions of the actors' bodies and are used extensively in dance lighting. Lighting from above and behind the actors, called backlighting, helps create the impression of distance between the actors and the scenery behind them, allowing the audience to perceive depth.
The general term for elements of scenery or props that are lit onstage is "practicals." Practical lighting can include floor and desk lamps, hanging fixtures, lighted signs, holiday decorations, television sets or anything else with a light inside it. Although these may appear to be controlled by the actors, they are most often wired into the lighting console and controlled by technicians. These elements add to the realism of the performance.
Safety becomes a major concern in a darkened public space. Safety lighting is used both backstage and in the audience area. Aisle lights, exit lights, stair lights and low-level lighting in the walls or at the edges of seating units are the most common types of safety lights in public areas. Dim or blue- or red-tinted lights are used backstage to allow actors and technicians to move around, read scripts and find props. These are known as "running lights." Other stage safety lights include any illumination that helps the actors locate dangerous pitfalls such as the edge of an orchestra pit for a musical or the front edge of the stage. These lights are often hidden from the audience's view by set pieces or tape.
Once the general illumination concerns are taken care of, stage lighting can be used to enhance the performance in many ways. It can denote location or time of day or season. It can enhance a mood through methods such as soft romantic lighting and flickering firelight looks or create a cold, impersonal atmosphere through stark bluish-white light. Special effects lighting can create illusions of fire, explosions, starry nights and other scenic elements onstage. It can also pull the audience's focus to a specific portion of the stage for specific scenes.