The same applies with lighthouses. Many lights had grates in the floor of the lantern room like the ones at Pt Sur. I know for a fact that Anclote Keys has similar though smaller prism holes. They allowed light into the watchroom from the lantern room. We have to remember that in the days before electricity your sources of light were either an open flame or the Sun. The Lighthouse Board probably did not like the thought of an open flame in the watch room, as this was where the keepers usually stored an amount of fuel sufficient to run the light through their shift.

At Big Sur when they started to restore the tower, only 2 of the old prisms were still in the tower. One was badly damaged and the other was almost impossible to remove. They took this intact prism to a glassmaker and had 180 made to place in the tower. It was at this point they decided to place a prism for those people or groups that donated a minimum of $1000 to the restoration fund.