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Although the use of the term limelight to indicate the theatrical spotlight is disappearing the concept is still very much alive.

Followspots in the days of gas lighting developed their very bright white light source by bringing a piece of Quick Lime (calcium oxide) to incandesence. The heat source that raised the lime to this point was carbide gas.  The same gas used in headlights on coaches. Carbide gas is created when Calcium Cabonate gets wet giving off a gas were cell acetylene. I'm sure you've heard of acetylene torches still used today to cut steel.

Adding a flat mirror behind the lime to reflect light forward and a plano convex lens to bend the light into a small and straightish beam. Put it on a simple yoke to obtsin pan and tilt control and you have stagelight that allows the performers to come down to the edge of the stage without losing their light.

 Limelights were first used at the Covent Garden Theater in London in 1837 or The Chestnut Theater in Philadelphia in 1816 depending on your source.

The Covent Garden Theater theater is the home of a theatrical history museum. What wonderful things they had to help create the mood. I've often been tempted to recreate the thunder machine except there is never enough pit or wing space. Now it's simply a matter of hitting the go button on the laptop.