Wednesday, August 9, 2017

The History of 19th & 20th Century Vault Lights (prism glass used in sidewalks) in the Chicago area.

Vault Lights, also known as Sidewalk Lights (or Pavement Lights in the UK), are those old glass prisms set into sidewalks to let light into vaults and basements below. Prisms were used instead of flat glass to disperse the light, diffusing it over a large area; plain flat glass would simply form a bright spot on the floor below, not providing much useful general lighting. 
Cross-cut of Basement using Vault Lights.
Invented in 1845 by Thaddeus Hyatt, sidewalk vault lights started being used in urban areas beginning around the 1850s and continued to be popular into the 1920s. The first vault lights were engineered to have glass blocks placed into a cast-iron framework.
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 rent-able in some cases. 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.

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.

Chicago locations where prism glass installations were known - via Google Map.





Compiled by Neil Gale, Ph.D.  

3 comments:

  1. The Brewster, located at 2800 N. Pine Grove (at Diversey) in Chicago, has glass block floors in its hallways. It also still has cage elevators. It's a gorgeous redstone building that has been in several movies.

    ReplyDelete
  2. Well remember them in the sidewalks of downtown Chicago. The musing always went to "What is under there?"

    ReplyDelete

The Digital Research Library of Illinois History Journal™ is rated PG-13. Please comment accordingly.
Comments not on the posts topic will be deleted as will advertisements.