Early 19th Century Glass Ship Deck Prism

Description

A deck prism, or bullseye, is a prism inserted into the deck of a ship to provide light down below. … more A deck prism, or bullseye, is a prism inserted into the deck of a ship to provide light down below.

For centuries, sailing ships used deck prisms to provide a safe source of natural sunlight to illuminate areas below decks. Before electricity, light below a vessel's deck was provided by candles, oil and kerosene lamps—all dangerous aboard a wooden ship. The deck prism laid flush into the deck, the glass prism refracted and dispersed natural light into the space below from a small deck opening without weakening the planks or becoming a fire hazard.
In normal usage, the prism hangs below the overhead and disperses the light sideways; the top is flat and installed flush with the deck, becoming part of the deck. (A plain flat glass panel would just form a single bright spot below—not the best option for general illumination—hence the prismatic shape.) less