In the days before electricity, light below a vessel's deck was provided by candles, oil, and kerosene lamps, which were all dangerous aboard a wooden ship. A clever solution for the lighting problem was the deck prism. Laid flush into the deck, small conical prisms drew light down below decks- without weakening the deck planks. Also available Deck Prism Base (Item# 4-9811) electrical base that illuminates Ship's Deck Prism (sold separately).