Coconut oil
Coconut oil was considered the best fuel for a lighthouse lamp because it made the light burn bright in the lighthouse. Gas lights were used later followed by dischargeable lamps. In the beginning, the lighthouse lamp had a steady flame. When ships began to confuse this with city lights, it was decided to use a flickering light in lighthouses. The lighthouses at Chennai and Mamallapuram use dischargeable lamps, which rotate inside a bowl of mercury. In recent days, LED lights are preferred.