The primary purpose of lighting is visibility. In a performance this can mean many things. Bright lighting can mean daytime, happiness, high energy, or a climax point in the performance whereas darker or obscure lighting can indicate night, danger, mystery, or a conclusion. Unlike other venues in which light plays a purely functional role, in theater and performance light is one of the performers.
The basic properties of light include intensity, form, color, direction, and movement. Each of these properties has a direct effect when experienced by the mind. The intensity and speed of movement of light can affect the level of alertness of the viewer. The effects of color on the emotions are well documented also. A skilled lighting technician will use both the technical knowledge of lighting effects and the social knowledge of what psychological impact these effects will have to design a lighting plan that will combine with and enhance the intentions of a performance.
The use of lighting in performance is limitless. Used in a quiet, introspective play, it can help the audience to relate to subtle emotion with slow fades, subdued hues, and indirect focus. Conversely, in a rock concert lighting is used to intensify experience through brightness, fast movement, strobes, explosions, and rapidly varying colors. Lighting is rarely the subject of a performance but is always present in some form and always affects the experience.
In the same way that a traditional Chinese muralist uses empty space to enhance form, a technician with an understanding of lighting will use darkness as well. Particularly in theatrical performances, a lack of light can be as effective as its presence. Using darkness to symbolize the darker side of existence, its mysteries and dangers, can be very effective.
Although the human emotions at the center of any performance change little over the years, the future of lighting design will be radically different. In the past 100 years we have gone from limelight to halogen, and in the next 100 the computerization and automation of lighting design will take it into territories unimagined today. Whether this leads to audience experiences that are also unimaginable remains to be seen.