In 1881 an electric lighting system was installed in the Savoy Theatre, based on the incandescent lamp. The light was controlled by variable resistors, called rheostats, which enabled individual control of each
lamp
or group of lamps, as well as centralized control of the entire lighting system.
Rheostat Control Board presented in the international exhibition in Munich 1882.
The rheostats, connected in series with the lamp, gradually dimmed the light by dividing the input
voltage
between the
lamp
and the resistance. The larger the resistance, the smaller the
voltage
across the lamps, thus reducing the intensity of the light. In the USA, rheostats were manufactured by Leonard Ward as early as 1894.
Theatres had to produce their own electric power on site, as public
electricity
distribution systems were only just beginning to evolve, and the theatre's
electricity
generator was usually located in the basement of the theatre, as were the rheostats, which were large and unwieldy. Needless to say, the
lighting operator
could not see the stage, and had to rely on the
stage
manager's cues when executing lighting changes.
A further disadvantage was that use of resistance for intensity control involved large power dissipation. Rheostats consumed the same electric power regardless of whether lamps were at full intensity or at a mere glow. Electric power not used by the
lamp
was dissipated by the rheostats, which produced a great deal of heat.
The electrical control switchboard at the Paris Opera, located under the stage, 1887.
