Acetylene is a highly combustible gas which burns with an intensely bright flame. (Think of the very bright flame that is used when a welder joins or cuts pieces of metal.) Acetylene is easily generated by the chemical reaction of water on a mineral called calcium carbide. This principle made it an ideal method for providing light in situations where human effort was not readily available. The solid calcium carbide, is cheap, easy to store, takes up relatively little space, and its reactant - water - is also readily available. Used in buoys and other automatic systems is straightforward and has been used in many systems for many years.