Bull's-eye lenses (usually plano-convex: flat on one side and convex on the other) are generally the oldest style, pre-dating prismatic shapes. When used as a deck light, the flat surface would be flush with the deck, with the curved lens hanging below, though Apsley Pellat's 1807 British patent "Lighting the Interior of Ships, Buildings, &c." uses the lens in the opposite fashion: "This illuminator is a piece of solid glass of a circular or elliptical form at the base, but the circular form is the most productive of light, and the strongest against accident; it is convex on the side to be presented outwards to receive and condense the rays of light, and has a flat or plane surface on the inside of the room or apartment, which it is intended to light."

Earlier patents (Wyndus 1684, Cole 1704) do not give any detail about the shape of the glasses used. Thaddeus Hyatt's famous 1845 patent ("Vault Cover"), the basis of the "Hyatt Lights" which made his fortune, used small bull's-eyes: "I prefer to make my illuminating glasses circular, and convex on one side".

Shown below is Henry Lanergan's lens of 1861 which features threaded sides and a protruding hexagonal boss, allowing damaged or worn-out lenses to be quickly replaced by simply unscrewing the old lens and screwed in a new one in. The smaller Lanergan shown below (3" diameter, 2" thick) is heavily worn on the working surface and was presumably removed from service and replaced; the larger lens (4" diameter, 2" thick) is only lightly worn and still perfectly useable.

A plain 6" bull's-eye lens is being produced today by Marine Skylights.

Pyramids usually in two nominal sizes, 3" and 4" (measured across the flats), although Thomas Laughlin Co. lists them in 3½" and 4½". I don't have any original examples of the larger size. This style has been reproduced in vast numbers, mostly from the lone surviving original prism on the Charles W. Morgan, now at Mystic Seaport. You can buy them wholesale from the Mystic Seaport Museum Shop, wholesale@mysticseaport.org, (800) 331-2665, or by the onesies at a thousand other places (just search for "deck prism").

My originals all have a sharp edge at the base and are somewhat crude, unlike the modern reproductions which have smooth, rounded base edges and are of uniformly higher production quality. Reproductions come in many beautiful but unauthentic colors which would be useless for anything except mood lighting.

This style prism looks very much like an orange juicer, aka reamer. I don't know the design's origins; it's not shown in any of my catalogs, nor do I know of a patent which covers it. My one example has a yellow tint that looks to be caused by selenium, the decolorizer which replaced manganese around WWI. Like manganese, which changes color after prolonged UV exposure (solarizing), selenium also changes color, turning straw, yellow or amber depending on the concentration. Selenium was used mainly post-war, around 1920-1930, with usage tapering off by mid-century.

The Mother of All Reamers below is 7¾" in diameter and weights 10¼#. This is much larger than the typical units which are 3 - 4" in diameter. It was reported to have been retrieved from the bottom of the Baltic. Is it Russian? There are no markings.

Reamers in a variety of sizes and depths are still made today by both Marine Skylights and Marshall Machine and Engineering Works. Nobody is making a Mother Reamer, however.

RECTANGULAR

The ribbed style appears in three of my early catalogs (Durkee, Laughlin and Tiebout) dating from 1915 to 1920, but I have yet to see any actual examples, nor have I seen any pictures of old ones installed in any ship. All three catalogs list exactly the same set of sizes: 6"×3", 9½"×2½", 10"×3", 10½"×3½" and 12"×4". Perhaps these three companies were all selling exactly the same product from a single manufacturer? They certainly look identical in the catalog drawings. This style does not appear to be in production currently.