The incandescent electric lamp is the modern invention which has radically changed stage equipment. Electricity is the one ele ment of production which makes the modern stage different from any that preceded it. (For its place as an aesthetic factor in modern stage design see p. 285.) The drastic changes in stage lighting (v. inf.) made possible by electric light result from the fact that the current can be run over coils of resistance wire (dim mers) and the intensity of light subtly changed from one moment to another, to fit the changing mood or accompany reaction of a play. Adolphe Appia was the first modern experimenter to indi cate the dramatic importance of this method of lighting plays and the technique of stage-lighting is still very largely a development of his ideas outlined in Die Musik and die Inscenierung.
The first electrical equipment consisted of rows of small powered incandescent lamps in narrow metal troughs (light bor ders) and hung in series of two or more rows parallel to the footlights which were relied upon to illuminate the actors' faces. These, with the other borders, were usually arranged in circuits of yellow (amber), white and blue—the lamps being dipped in a transparent dye—and each circuit dimmed or cut off to change the colour of any scene. The various drawbacks of this system were that the footlights, if sufficient to light the actors, flooded the settings with needless brilliance, casting shadows behind them. The whole stage being flatly and evenly lighted, contrast and emphasis became impossible. This type of light is very fittingly known as flood-lighting.
The development of incandescent spot-lamps has greatly im proved lighting. These consist of high-powered bulbs of zoo, i,000 and 1,5oo watts in a metal hood which can be tilted to any angle, the light projected through a lens focused upon any given stage area. (A smaller, 25o watt type is known as a baby-spot.) The area of light can be spread or be narrowed down to the size of a face. Spot-lamps were at first mostly used on a light bridge hung just inside the proscenium frame, where the electricians (operators) could walk to and fro and re-angle them as needed. Owing to the steady rise in the cost of labour it is a common practice to use more lamps previously set and angled for successive scenes. Some are hung from a bridge or iron pipe overhead. But, as these tend to cast heavy shadows in the sockets of the actors' eyes, groups of Jo to 20 are mounted in a standing iron pipe (light tormentor) on each side of the stage (see diagram). Footlights are kept low and reinforced by additional spot-lights from the front of the first balcony or the ceiling of the theatre if space has been provided for them. In a recent production of Faust (at the Theatre Guild,
N.Y., 1928) 8o spot-lights were used for its 17 scenes on the fore-stage alone.
The effectiveness of spot-lighting depends entirely on the flexi bility of lighting control; i.e., the dimmer. The only satisfactory system is to have each spot-light controlled by a separate dimmer so that every lamp can be brought independently to the degree of intensity required. But for complete changes of light, groups of lamps must be dimmed together. Hence the nerve centre of stage lighting is the dimmer-board, where the switches and dimmers are grouped; it may be compared to the sensory and motor nerve system of the body. The most important and difficult piece of mechanical construction in the modern stage equipment is this switch-board and dimmer-board and the coupling of both so as to obtain the greatest ease in controlling the lights in any desired order or grouping.
The American type of dimmer is not the most effective. In this the resistance, divided into ioo steps (called a dimmer-plate), is wound in direct connection with the handle that controls it, and then banked in rows behind the face of the board. They are heavy and cumbrous, and tend to overheat rapidly. The Theatre Guild switch-board of 102 dimmer-plates is II ft. long and 6 ft. high. Coupling or interlocking handles to bring down groups of lamps in unison involves much friction and is cumbersome to operate even in its most compact form. The German system of control perfected by Schwabe and the Allgemeine Elektrizitats Gesellschaf t, is mechanically a great improvement. The resistance coils are stacked underneath the stage floor (or above it) in a fireproof chamber. A carbon-brush contact is connected by a fine cable brought to the stage over pulleys and wound on a counterweighted circular drum which serves as an indicator. As this indicator handle is shifted the contact brush in the cellar slides up and down. The great advantage of this system is that the indicator coils are small, being only cable controls, light in weight, and easy to move; the circular indicator is one-third the size of a standard American dimmer-plate, so that a bank can be easily brought within the reach of a mechanician, and the gearing of any group of them is mechanically much simpler and easier to move. Valuable stage space is saved by having the resistance coils in the cellar. They can be made larger, the number of steps increased and the dimming of light be advanced almost imper ceptibly. This system is now being copied in England. It is to be hoped that its adoption will soon be universal.