If something is In The Limelight it's the centre of attention or in the public eye. When lime (calcium oxide) is heated, it produces a bright white light and in 1826 a Scottish army engineer called Thomas Drummond used this discovery to aid map-making in poor weather. The intense limelight could be seen from a long way away and was used to mark out distances accurately. Shortly after this, scientists developed his invention to produce other powerful lights. These were then used in lighthouses and later as spotlights in theatres, to focus attention on the main actor. Therefore, a person standing "in the limelight" was at the focus of attention.