The phrase "in the limelight" means being the center of attention or in a prominent position where one is observed by many people. Its origin is rooted in the theater and stage lighting technology of the 19th century. 

In the early 19th century, before the advent of electric lighting, theaters used a form of stage lighting known as "limelight." Limelight was created by heating a cylinder of quicklime (calcium oxide) with an oxyhydrogen flame, which produced a bright, white light. 

This intense light was used to illuminate the stage and highlight the actors. The invention of limelight is attributed to Thomas Drummond, a Scottish engineer, who developed it in the 1820s. Limelight quickly became popular in theaters due to its brightness and ability to focus light on specific parts of the stage, effectively putting actors "in the limelight."