Invented by Thomas Drummond in 1826, limelight (or calcium light) was not regularly used in London theatres until much later. It was adopted by American troupes after the Civil War, but was gradually replaced by the cheaper carbon arc light. The bright glow of limelight, directed through a lens, was produced by heating a block of limestone to incandescence with the spark of combined oxygen and hydrogen through hoses from their separate containers, allowing it to give off a misty white light. American theatres employed limelights during the later half of the 19th century mostly for spotlighting leading players. The term "in the limelight" is frequently employed to suggest an actor at the center of attention.
See also lighting.
The Historical Dictionary of the American Theater. James Fisher.