Vault Light Restoration

When walking along the streets of any major metropolitan city around the world, you may notice small glass “bumps” that are slightly raised above the sidewalk. In other cities, you might also notice some purple-hued glass squares that are flush with the concrete. These historic elements are known as vault lights, and they were once widely adapted as cities became industrial hubs in the early 1900’s. City leaders and building owners have recognized both the historical and aesthetic value of vault lights, and many have begun the process of restoring those sidewalks to their former glory by restoring or replacing these unique panels.

Concrete pavers installed at a private residence in Boston, MA

What are Vault Lights?
Vault lights were originally known as prism lights or prism glass. A prism light is an architectural glass element that is used to redirect daylight into interior spaces through reflection and refraction. Standard flat glass simply forms a bright spot on the floor below; however, the prism disperses light more evenly. This design strategy is known as daylighting. An architectural practice that remains popular to this day, daylighting was extremely important before the widespread availability of electric lighting.

The earliest forms of vault lights were originally created for use on the sea. Known as deck lights, these forms of prism glass harnessed natural light to light a ship’s interior, providing a safer manner of lighting that no longer required the use of oil lamps or flames. Because ships were often coal-carrying, the vault lights were incredibly useful. The glass served a dual purpose: it not only lit the lower portion of a ship, it also provided a view of a potential cargo fire to the ship’s occupants on deck.

The Popularization of Vault Lights
The idea of daylighting was eventually brought to land around the turn of the 20th century during the industrial revolution. At this time, building codes allowed for basements to extend beneath sidewalks. Open grates were originally used as a way to provide light to basements, but these presented several obvious problems. They allowed in water and street debris from the street, and they were difficult for pedestrians to walk on.

The more common vault lights we know today are an adaptation of Thaddeus Hyatt’s 1845 invention. These vault lights were easier to walk on and protected the areas below from water. The original vault light glass design incorporated a prism shape on the bottom to diffuse and spread the maximum amount of light through a broader area. Sometimes, multiple prisms would be set at different angles to spread the light more evenly throughout a larger space.

Vault Lights in New York City


The use of vault lights became widely adapted among many major cities in the United States and across the globe. These cities include New York City, Philadelphia, PA, London, UK, Dublin, IE, Sydney, AU, Seattle, OR, San Francisco, CA, and Portland, OR.

In these cities, vault lights are set into concrete or cast iron panels, and those panels are set into the sidewalk.

Changes Over Time
Vault lights were popular in many cities from the late 1800’s through the 1930’s. However, as modern conveniences like electricity became widespread, the use of vault lights became less frequent and the number of manufacturers dwindled.

A common feature amongst vault lights is their unique shade of purple. Purple glass was originally manufactured to be clear, but changes color over time due to a chemical reaction that occurs within the glass. The manganese oxide, which was added as a decolorizer, in the glass slowly turns purple after years of UV exposure from sunlight.

Prism glass


As one would imagine, a century of foot traffic and weather elements have caused wear-and-tear on the vault lights and panels. The lack of yearly maintenance, the absence of heat, accumulated moisture, and sidewalk and skylight leakage have led to the evolution of the vault lights in cities across the globe. Both cities and historical societies have taken some measures to begin the process of repairing and restoring their damaged vault lights.

The panels vary in condition from city to city – some remain intact with no visual damage, while others are noticeably damaged with some vault lights completely missing. Because they are specialty architectural structures, it is crucial that any company looking to undertake a vault light restoration have a proven history of completing these projects before they are specified.

In certain instances, restoration attempts were made to replace broken or missing vault lights. Because the maintenance responsibility often falls on building owners, the state of vault lights varies from panel to panel. In an attempt to repair them, some vault lights have been covered with asphalt, tar, wood, concrete, or pieces of sheet metal.

Returning Sidewalks to their Former Glory
The practical motivation for replacing or repairing vault light remains the same as a century ago. New or rebuilt vault lighting lenses will still admit much needed natural light into dark spaces and accomplish this without consuming the energy required for artificial lighting. Replacing weathered panels with new ones has been facilitated by modern glass technology.

Today’s vault or pavement lights can be precast or even cast in place in concrete or steel frames. The lenses are created from solid glass or load-bearing sealed hollow glass pieces that can be designed to diffuse admitted light in virtually any direction. Shapes may be circular, square, triangular, or even irregular to accommodate various designs.

Precast concrete with glass pavers installed at Hillshire Farms Headquarters in Chicago, IL

GBA Architectural Products + Services, The Vault Light Restoration Experts
GBA Architectural Products + Services represents many of the world’s most important architectural glass manufacturers. Suppliers of structural glass, glass block, and LightWise glass systems, GBA is also an active component of vault light restoration throughout North America. The professionals at GBA are prepared to collaborate with cities and building owners to restore these essential historical features and can duplicate original designs with the most durable and functional vault glass panels.

Today’s glass block designs and choices from GBA Architectural Products + Services are durable enough for any purpose and can add light and beauty to any project.

Visit the GBA Architectural Products + Services website to learn more about the favorable contribution glass products are making to the world of architecture. Request product information on the GBA website by filling out the online form.

Contact GBA Architectural Products + Services for more information about glass architectural products.

For questions, call the experts at GBA:

East Coast: (212)-255—5787
Midwest: (877)-280-7700
West Coast: (213)-634-7050