In the 19th century, burgeoning cities on both sides of the Atlantic had to solve the problem of lighting underground spaces, such as basements, tunnels, and other dark “vault” areas under urban streets and sidewalks. Of course, there were open flame light sources; however, a less-flammable alternative from the shipbuilding industry inspired city planners of the era.
Glass pieces called “vault” lights were invented in 1845 by Thaddeus Hyatt to provide illumination below a ship’s deck without potentially setting the vessel ablaze.
Following Hyatt’s lead, city planners and architects designed and shaped glass prisms to disperse and bend light throughout a dark subterranean or “sidewalk vault” space. They set prismatic discs into iron grates or interlocking iron discs that could be linked together to form a walkable surface. The glass pieces were sometimes slightly curved at the walking surface and angled on the bottom to “throw” light into the darkest corners. Sidewalk vault lights became a common sight in cities across North America from the 1860s through the 1930s.
Some of the original glass dating back to the vault light era still exists in cities like New York and Chicago. Many were paved over during World War II to make cities less visible to potential Axis bombers. Others became chipped, loose and obsolete in the decades after the introduction of electricity and were haphazardly patched with concrete, wood, or asphalt–usually to poor effect.