Original Small Green Deck Prism

A Deck Prism is a prism inserted into the deck of a ship, which provides light down below.\r\nFor 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 limited. Light below a vessel's deck was provided by candles, oil and kerosene lamps - all dangerous aboard a wooden ship. The deck prism was a clever solution. Laid flush into the deck, the glass prism refracted and dispersed a flood of natural light into the cabin below from a small deck opening without weakening the planks or becoming a fire hazard.\r\nIn normal usage, the prism hangs below the ceiling and disperses the light sideways; the top is flat and installed flush with the deck, becoming part of the deck. A plain flat glass would just form a single bright spot below-- not very useful general illumination-- hence the prismatic shape.