The actor must be seen in the proper relationship to his background when he walks onstage. This relationship, of course, is different for each play. In general, the designer turns to the manipulation of intensity, distribution, and color of the lights for each situation. The main importance is the distribution of light, because it involves the angle and direction of the light reaching the actor to reveal him, especially his face, in natural form.
Lighting the face in natural form is the goal. It means the actor's face should be seen as it appears under natural lighting. We are used to seeing people lit from above, whether by sunlight or the lights of a room. We are so used to seeing people lit from overhead that when we see someone lit from below, the lighting on her face appears unnatural.
If you have ever photographed anyone outside, you know that you must position the subject where the sun will reveal his face most favorably. If the sun is too bright from a certain direction, it can cast deep shadows on the subject's face. If the day is overcast, the face might miss the dramatic accent otherwise achieved by brilliant sunlight. We can control the proper angle of the light on the face via the proper use of stage lighting.
By altering the intensity and distribution of light on the stage, the face of the actor can be lighted as it is in nature. It has long been a practice of artists and architects to render their drawings as though light were falling on the subject from over the artist's shoulder at an angle of about 45 degrees. The lighting designer adopts the same concept. Through the use of a specific lighting instrument, like a spotlight, the beam may be directed on the actor at a 45-degree angle above and at 45 degrees from the right and left. To give the face an accent of brightness or color difference on one side, the intensity or color of the right or left spotlight may be varied. The face is then disclosed by a wash or fill light on one side and an accent or key llight on the opposite side. This slight difference in color and intensity not only improves the visibility of the face, but also adds interest to the composition.
Cross lighting in the modeling of the face is the beginning technique for the lighting of the actor. A third angle can be employed to further define the actor by lighting him from overhead and behind. Back lighting is a stratagem borrowed from movie and television lighting. Because of the need to separate the actor from his background, it is a necessary angle in television lighting. The use of back lighting on the stage to separate the actor from his background also adds another dimension to the stage composition. It allows the lighting designer to put a brighter light on the background than he could otherwise, and it permits the scene designer to use colors without fear of failure to bring the actor's face into relief. Back lighting produces highlights on the head and shoulders of the actor that give a halo effect if the light is too intense. When it is kept in proper balance with the front lights, the actor is etched clearly against the background.
Sidelights are a compositional plus, and can add the appropriate accents to produce the desired effect. Macabre, horrific or mysterious settings are perfect for the use of sidelights. The same is true when it comes to lighting from below. A character can appear more menacing if illuminated in a low-light situation, and more mysterious when only lit from the side. This type of lighting breaks the standard viewing of a face when lit for natural composition.