The basement level of the lighthouse was also referred to as the first floor, even though we now think of the galley level as first. The basement is actually contained within the cast iron cylinder and, thanks to the height of the breakwater, visitors are actually standing even with the basement level when next to the lighthouse.
The basement is lined with brick to a thickness of around 24 inches. There were three small windows in the cylinder, but most have been sealed in recent years. There was also a hatch near the basement ceiling on the east side to permit coal to be transferred directly into the basement from a supply barge or boat alongside. There are also two small storage closets and a small room that might have functioned as a workshop or supply room for performing routine maintenance on the lighthouse
The center of the basement floor holds a cement pad that probably held either a compressor or a small generator. The actual use is uncertain, though the Trust is attempting to ascertain the exact purpose of the pad.
The most remarkable features of the basement are two brick-lined cisterns embedded in the basement floor. These cisterns held the only water supply for the
lighthouse. Water was collected in a gutter around the circumference of the roof of the main gallery and fed into cast iron pipes that drained the water into ceramic pipes leading to the cisterns. Water from the cisterns was then retrieved by a handpump next to the sink in the galley.
Today, the basement holds supplies used by the Trust. There are also two banks of batteries, charged by the solar panels that were installed nearby on the breakwater in August 2010. These batteries are capable of meeting the electrical needs of the entire lighthouse.
Due to the steep, narrow stairs and the presence of electrical equipment, the basement is not open to the public.