The term "limelight" originated from a type of stage lighting that was widely used in the 19th century. It was a popular method of creating bright illumination for theatrical performances, lectures, and other public events before the advent of electric lighting.
Limelight is created through a chemical reaction involving burning a mixture of oxygen and hydrogen gases and directing the resulting flame onto a cylinder or rod of calcium oxide (quicklime). When the calcium oxide is heated to a high temperature by the flame, it emits an intense white light. This bright and focused light allowed performers to be well-lit on stage, making them the center of attention or "in the limelight."
The term "limelight" became a metaphor for being the focus of public attention or the center of interest. Today, we still use the phrase "in the limelight" to refer to someone who is in the spotlight, receiving public attention, or under scrutiny. However, modern stage lighting has evolved, and electric lighting has largely replaced the use of limelight in theatrical productions.