|Cross-cut of Basement using Vault Lights.|
Later, with the introduction of Portland cement, setting them into reinforced concrete panels was more common.
These “glass blocks” provided a way to get light into the useful basement and void areas under the sidewalks. This also made the space rentable in some cases. The first attempts at vault lights proved unfruitful because the design basically allowed a single shaft of light to shine straight down into the space below.
|Marshall Field Vault Lights on State Street, Chicago.|
With Hyatt’s invention, the design incorporated a prism shape (“saw-tooth”) on the underside while the surface above remained smooth to walk across.
This provided a way for the light to be directed over a broader area in the dark underground.
The idea caught on; by the late 19th century they were common in larger cities downtown areas, especially cities like Chicago, New York, and San Francisco. Their use declined as electric light became cheaper and better, and by the 1930s they were not considered in construction any longer.
Now, they are now endangered architectural relics.
|Vault lights on the second floor of the atrium of The Rookery Building, Chicago.|
Compiled by Dr. Neil Gale, Ph.D.