It was here that he invented the oxy-hydrogen blowpipe. It was a system for burning a jet of oxygen and hydrogen to produce an intensly hot flame. He experimented with it on different substances and found that when the flame was played on a chunk of lime, a brilliant light was produced. Gurney had invented limelight. It was the use in lighthouses which brought about Gurney's most famed invention - the Bude Light.
Limelight presents a few practical problems.
Once the limelight is burning, you have to gradually feed in more lime as it is consumed by the hot flame. Gurney solved all these problems with his Bude Light, named after the town in Cornwall where he built his castle. He used an oil lamp as his basic flame producer, a well known technology at the time. He then introduced oxygen gas into the middle of the flame. Gurney use a single Bude Light to light his castle.