From Merriam Webster:
Main Entry: 1 lime·light
1 a : a stage lighting instrument producing illumination by means of an oxyhydrogen flame directed on a cylinder of lime and usually equipped with a lens to concentrate the light in a beam b : the white light produced by such an instrument c British : SPOTLIGHT
What function does the “cylinder of lime serve”? Does it fluoresce or what? Has anyone ever seen one of these things?