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How was quicklime used in 19th-century limelight stage lighting?

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A labeled diagram of the periodic table entry for calcium, showing its atomic number 20, symbol Ca, atomic weight 40.078, electron configuration, and classification as an alkaline-earth metal. Icons indicate calcium is a solid with a face-centered cubic crystal structure and strongly basic oxides at room temperature. — calcium The chemical element calcium is the most abundant metallic element in the human body.

In 19th-century stage lighting, limelight was produced by directing a sharp, intense oxyhydrogen flame against a cylindrical block of calcium oxide, commonly known as quicklime.12

The heat from the flame caused the lime to reach incandescence, emitting a soft, brilliant white light. Because the light originated from a very small area, it could be effectively focused using a mirrored reflector, allowing it to be directed from the auditorium onto the stage. This intensity and focus made it the first true theatrical spotlight, ideal for highlighting individual performers or creating realistic environmental effects like sunlight and moonlight.13

The use of limelight required significant manual labor; an operator had to constantly tend to the gas cylinders and slowly rotate the block of lime as it was consumed by the flame to ensure a fresh surface was always exposed. By the late 19th century, this labor-intensive system was largely replaced by electric arc lighting.13