Starting in the early 1890s the lights were provided by burning acetylene gas generated in situ from calcium carbide reacting with water. The acetylene-gas illumination system could reliably be turned on and off automatically, enabling automated unattended lighthouses to be used. Once electricity became available, often provided by one or more diesel electric generators in remote locations, the light source was gradually converted to electrical power and the clockworks were run by some type of electric motor. For example, of modern changes, the Chatham Light in Chatham, Massachusetts (near the "elbow" of Cape Cod) the light was converted in 1969 from its Fresnel lens light assembly to a Carlisle & Finch DCB-224 rotating light generating over 2.8 million candela. This is visible for over 20 nautical miles on a clear night and has a self-changing bulb assembly to replace burned-out bulbs.