The lighting designer is one of the most important people involved in the production of a play, and one of the most under-appreciated. In many plays, the best lighting is what seems most natural, and often goes unnoticed. The lighting designer's contributions to a piece of theater provide a vital sense of realism, mood and tension.
The primary purpose of theatrical lighting is to make certain that the actors are visible. This seems obvious, but it is important that the designer has ensured that all areas of the stage and all actors on that stage can be seen when the lights are at full.
Time and Place
Lighting is also vital to establishing the setting of a play. Lighting tells the audience whether they are inside or outside, what time of year it is, and what time of day it is. Depending on the lighting (including light from set pieces), the lights may even help to establish what period in time the play takes place.
Lights are the most effective way to set the mood or tone for a play or for any given scene. Natural light can give a sense of normalcy, while the use of gels in dark greens or purples can give a scene an unsettling, otherwordly feel.
Lighting can be used to execute a variety of stage directions and special effects. These can range from weather (lightning, snow, rain, clouds) to fire to the illusion of explosions or gunfire.
The absence of light can also be a useful tool. By darkening certain portions of the stage, the remaining illuminated areas become focal points, thus directing the attention of the audience.