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Prism glass is architectural glass used to redirect sunlight to interior spaces through refraction and reflection-- "daylighting". Before electric lighting became common around 1900, light was provided free of charge by the sun, and at night by candle, lamp, or other flame. Penn Station in 1938 was a glorious example-- the glass roof lets in sunlight which falls through the glass-embedded floor and illuminates the tunnels below. Since sunlight is obviously superior, while flames are dim, expensive, and dangerous, anything which could extend the reach of the sun's free and safe light to interior spaces would make that space more useful and valuable. Deck lights were the first form of prism glass-- the earliest known patent is Wyndus' of 1684: GREAT AND DURABLE INCREASE OF LIGHT BY EXTRAORDINARY GLASSES AND LAMPS; sadly, the details are not specified, it's four pages of dense legalize. The first U.S. patent is Rockwell's of 1834; only the damaged drawing page remains, but it's worth seeing: a single large round jewel set in a round iron cover. Fire at sea is disaster, more so on a wooden ship or with a flammable cargo. Safely lighting a ship's interior with daylight and prisms instead of flames was a practice widely adopted. Colliers and lime cargos were especially dangerous (slaking lime becomes very hot), and the glass worked two ways: to daylight the hold, but also in the other direction, to show on deck if the cargo were on fire. Eventually the idea spread to land as vault lights, aka sidewalk lights or pavement lights. They're those glass chunks set into old downtown sidewalks to let light into vaults and basements below. You've probably noticed them-- usually grids of purple squares-- and walked over them, but not known what they were for or were called. The most familiar type of prism glass is "Luxfer tiles" (actually made by several companies, like this American 3-Way Prism Company signature tile). More correctly "prism tiles", they were introduced in 1897 by the Luxer Prism Company, using Pennycuick's 1885 patent. The idea was very successful and the tiles widely used. Plain tiles without a pattern on the front are common still, as are a few patterns, notably panel and raindrop, but some are very rare. Frank Lloyd Wright penned 41 designs for Luxfer, however only one was produced, a stylized flower; fortunately, it's also fairly common. The Fresnel lens was developed by Augustin-Jean Fresnel in 1822 for magnifying lighthouse lanterns. It is essentially the outer surface of a large double-convex lens, without the core glass. It functions as the whole solid larger lens would, and makes it possible to build compound lenses much larger than a single lens could ever be.