Deck Prisms
These deck prism arrays were placed in the iron decking at the top floor of the lighthouse, surrounding the large Fresnel lens. The prisms, flat on the surface but faceted below would refract light into the lighthouse tower and its spiral staircase below.
"In 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.
The names "deck light" and "dead light" or "deadlight" are sometimes used, though the latter seems to be uncommon as a reference to prisms, as more often refers to plain-glass panels.
The earliest deck prisms with provenance are from the 1840s. Presumably they were used earlier, but how much earlier is unknown; the origin of the idea is lost, and glass is difficult to date." glassian.org/Prism/Deck/index.html
I was fascinated by the beauty, artisanship, and function of these, and had a difficult time finding information on the internet about their use in lighthouses.
By the way, this is not selective color. I'm not a fan of selective color, I did only a slight bit of dodging on the image. The details are much clearer when viewed larger on black.
Deck Prisms
These deck prism arrays were placed in the iron decking at the top floor of the lighthouse, surrounding the large Fresnel lens. The prisms, flat on the surface but faceted below would refract light into the lighthouse tower and its spiral staircase below.
"In 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.
The names "deck light" and "dead light" or "deadlight" are sometimes used, though the latter seems to be uncommon as a reference to prisms, as more often refers to plain-glass panels.
The earliest deck prisms with provenance are from the 1840s. Presumably they were used earlier, but how much earlier is unknown; the origin of the idea is lost, and glass is difficult to date." glassian.org/Prism/Deck/index.html
I was fascinated by the beauty, artisanship, and function of these, and had a difficult time finding information on the internet about their use in lighthouses.
By the way, this is not selective color. I'm not a fan of selective color, I did only a slight bit of dodging on the image. The details are much clearer when viewed larger on black.