The limelight was invented by Thomas Drummond in 1816. The light consisted of a block of calcium oxide heated in jets of burning oxygen and hydrogen to produce a soft and brilliant light. Each limelight required its own operator to adjust the calcium oxide block and maintain the gas cylinders that fueled it. It was used in theaters from 1837 until it was replaced by electric lighting at the end of the 19th centruy. The expression "in the limelight" referred to the most desirable area onstage, the front and center, which was illuminated by limelights.