Deck prisms are molded glass pieces that reflect light into the lower parts of a ship, used before electricity. They are multi-sided and come in various shapes and sizes. Original prisms are rare, but reproductions are sold as decorative items.
A deck prism, also known as a dead light or deck light, is a piece of molded glass that reflects light into the lower reaches of a ship. It was used on wooden boats before the availability of electricity as a safer alternative for lighting than kerosene and oil lamps or candles. Prisms have a flat base, which rises to a smaller, pointed or rounded top. They were usually hung from the ceiling, under a small hole in the canopy, with the pointed side hanging down so that light could enter from above. Deck prisms are multi-sided so that light passing through the base can reflect off multiple surfaces below the deck.
Although the earliest versions of the cover prism date back to the 1840s, it is believed to have been in use many years, and possibly centuries, before then. Original deck prisms are rare and hard to find, although there are a few that can be seen in nautical museum collections. It can also be challenging to determine its age, as the glass is not easily dated. There has also been no solid information on how cover prisms were developed or who, if anyone in particular, was responsible for their invention.
All canopy prisms are multi-sided to allow for even distribution of light below the canopy. Otherwise, they can come in a variety of shapes and sizes. A typical cover prism will have a circular base with a domed or pointed top. Some have a rectangular base that rises up to a three-dimensional triangle.
From the top side of the platform, the prism will appear as a flat piece of round or rectangular glass. Below deck, it looks similar to a lamp. It can be secured to the deck or hung from a bracket. There may be one or more deck prisms on a ship, generally depending on the size of the ship.
The deck prism is still used on some sailboats, but mainly as a nostalgic decorative element. Although not intended to replace electricity, prisms can help illuminate below-deck areas and potentially save on energy costs. Traditional deck prism reproductions are also sold as decorative items for nautical enthusiasts. They are usually mounted so that they can be hung from a special bracket or sit upside down on a pedestal. Prisms are also marketed in a variety of colors and are even incorporated into novelty items like Christmas decorations.
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