One wouldn’t think that such an ordinary every day thing such as a vault lights would be so intriguing, especially as they are essentially just windows in the ground. But these foot worn, unnoticed paving stones could in fact be windows into our past and may shed light on more than just the floor below.
Lets start with the Wiki Quote:
Pavement lights (UK), vault lights (US), floor lights, or sidewalk prisms are flat-topped walk-on skylights, usually set into pavement (sidewalks) or floors to let sunlight into the space below. They often use anidolic lighting prisms to throw the light sideways under the building. They were developed in the 19th century, but declined in popularity with the advent of cheap electric lighting. Older cities and smaller centers around the world have or have had pavement lights. Most such lights are approximately a century old, although lights are being installed in some new construction.SOURCE Wikipedia
The first vault light was patented in 1834 by Edward Rockwell, reports Glassian, a site devoted to glass collections and glass history. It was a round iron plate surrounding a large glass lens.
In 1845, Thaddeus Hyatt proffered his own patent application complaining that Rockwell’s lights were easy to fracture. He instead proposed an iron plate containing small glass pieces, protected by protruding iron knobs. Those are the lights you’re most likely to still see today.Source Treehugger.com “What Those Beautiful Glass Prisms in the Sidewalk Are Really For“
So what do we know about vault or paving lights?
We know cities such as New York, San Francisco, Chicago, Philadelphia, Seattle, London, Dublin, Amsterdam, Toronto have such installations. But how many other places still have these?
Paving lanterns would mean a road and pavement could be laid over the mud (see MFT), and light could still be provided to the submerged floor below.
You can find these by simply looking down.
“The glass pieces are vault lights, sometimes called pavement lights in the U.K. They were inserted into the sidewalk to allow light into the basement areas below ground.”Source TreeHugger.com
The top of the vault lights are flat with the sidewalk so that people can walk right over them, but the bottom often has a different shape.
Over the years, as the manganese is exposed to ultraviolet rays, it turns purple or even pinkish, KQED reports. This can be a good indication of the age of the installation, although replacement glass can sometimes be dyed to give it the aged look.
As electricity was re-introduced during the 1930’s, many vault lights were covered over and removed. The original design allowed for the individual glass refactors to be replaced.