|
Prism Glass Types |
|
| Prism Glass Makers |
|
|
Reference |
|
|
Repair/Restoration |
|
|
Construction |
|
|
Collection Gallery |
|
|
In Situ Gallery |
|


|
|
|
|

Penn Station, 1938
|
Prism glass is architectural glass used to redirect sunlight to
interior spaces through refraction and reflection-- "daylighting".
Before electric lighting became common around 1900, light was provided
free of charge by the sun, and at night by candle, lamp, or other flame.
Penn Station in 1938 was a glorious example-- the glass roof lets in
sunlight which falls through the glass-embedded floor and illuminates
the tunnels below.
Since sunlight is obviously the superior light source, while flames are
dim, smelly, smoky, expensive and dangerous, anything which could extend
the reach of the sun's free and safe light to interior spaces would make
that space more useful and valuable.

Group of original deck lights,
bottoms shown (tops are flat)
|
|
Deck lights were the first form of prism glass-- the earliest known
patent is Wyndus' of 1684: GREAT AND DURABLE INCREASE OF LIGHT BY EXTRAORDINARY GLASSES AND LAMPS;
sadly, the details are not specified. Fire at sea is disaster, more so
on a wooden ship or with a flammable cargo. Safely lighting a ship's
interior with daylight and prisms instead of flames was a practice widely
adopted. Colliers and lime
cargos were especially dangerous (slaking lime becomes very hot).
The glasses work both directions: they daylight the hold, but also show on
deck any light from a cargo fire.

Before: open grate |
Eventually the idea was adapted for land use as vault lights
(UK pavement lights). Light used to be provided to vaults
and basements by open grates, which were difficult to walk on
(especially with women's shoes) and obviously let in water. By
placing glass lenses in an iron (or later concrete) frame, daylight
could be introduced below while excluding the weather. Iron nubs
protruding above the glass surface protect the glass and aid traction. |

After: vault lights |
In 1834, E. Rockwell patented a round iron plate with a single mammoth
bulls-eye lens, but Hyatt later complained in his own patent application,
"These glasses are extremely liable to fracture, and when broken leave large and dangerous openings within their rims...".
Rockwell's plate apparently did not not see widespread use; only three
examples of the iron are known to exist today, and none of the giant glass
jewels.
 |
|  |
|  |
Thaddeus Hyatt
(Library of Congress) |
Thaddeus Hyatt's
patent basement extension |
Brown Brothers #4
21" Hyatt Light |
As an improvement on Cornell, Thaddeus Hyatt in 1845 patented his
Vault Cover, an illuminated
iron plate set with numerous small, tougher bulls-eye lenses, protected
with protruding iron knobs. His Hyatt Lights worked well and were
a hit; they made him a rich man. From the 1850s on, Hyatt spent much of
his time and fortune fighting for abolition of slavery.
The next big advance was Hayward Brothers' 1871 Improvements in Pavement
Lights. Pendant prisms had been tried before but did not work well.
Edward Hayward's idea was to use a semi-prism shape instead: "...the
object of my Invention is so to construct them [prisms] that they may not
simply allow the light to pass through, but that they may also direct the
light in an inclined direction into the rooms it is desired to light."
Using a combination of internal reflection and refraction, the prisms
could re-direct and disperse light from the vertical to the horizontal,
throwing light from the one bright area deep into the backs of otherwise
useless spaces.
 |
|  |
|  |
Vault lights construction
New York City, 1907 |
Display of vault lights,
deck prism, coal plates, etc. |
Illuminated sidewalk lift
Etna, California, 2010 |

Am. 3-Way Prism Co
Trademark tile
|
The most familiar type of prism glass is prism tiles, which take
the reflection/refraction idea of semi-prism vault lights and applies it
to vertical windows.
They were based on Pennycuick's 1885 patent
for window glass with horizontal prisms on the inner surface, and introduced
commercially in 1897 by the Luxfer Prism Company.
They were an instant success and the tiles were very widely used. Prism tile
installations can still be seen in many small towns where they were especially
popular as transom lights above storefront windows. Like vault lights, prism
tiles take concentrated light from the sky which falls at the front of a room
and redirects and diffuses it to the darker parts of a space.
Sometimes called "Luxfer tiles", they were also made by the
American 3-Way Prism Company
(with whom they later merged), Solar Prism Company,
Condie-Neale, Jupiter Prism Company and others.

Fresnel 2nd order
Lighthouse lens
|
The Fresnel lens was developed by Augustin-Jean Fresnel in 1822 for
magnifying lighthouse lanterns. It is essentially the outer surface
of a large double-convex lens, without the core glass. It functions
as the whole solid larger lens would, and makes it possible to build
compound lenses much larger than a single lens could ever be.
|