| You've most likely seen them in a theatre or auditorium, or a movie that takes place in a theatre or auditorium. At the back of the auditorium, someone is pivoting a large bright spotlight to follow an actor or performer across the stage. Because of the follow spot's size and need for mobility, the operator usually controls the size, shape, intensity, and color of the light independent of the lighting booth.
Before electric bulbs, follow spots used a burning flame of oxygen and hydrogen applied to rotating cylinder of lime-- putting the actor onstage in the limelight. | 
