{{Short description|Flat-topped skylights designed to be walked on}} {{Use dmy dates|date=October 2019}} 300px|thumb|upright=1.3|alt=view down onto a sidewalk with vault lights; a slab of concrete with a regular grid of inset squares of slightly domed purple glass. Within each square, faint vertical lines can be seen through the glass, and points of light shining up through the glass are duplicated in horizontal lines of three points of light. Some yellow leaves have fallen on the damp concrete.|Sidewalk prisms from above, with lights shining up from inside the hollow sidewalk. The purple shade has developed over a century. These are multi prisms; the ridges can be seen running vertically {{see below|{{section link||Transparent elements}}}}.'''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 in the early 20th. Older cities and smaller centers around the world have, or once had, pavement lights.<ref name=glassian_gallery /> In the early 21st century, such lights are over a century old,<ref name=recon /> although lights are being installed in some new construction.<ref name=NYT />[[File:Hyatt patent basement extension.gif|thumb|upright=1.3|alt=Cross-section of a road and adjacent building, showing the basement extending under the sidewalk and part of the road. Sunlight is shining through the sidewalk into the basement.|A sidewalk vault, which is daylit through vault lights, 1880]]
== Uses == {{multiple image | width = | footer = The Westlake Square Comfort Station in Seattle, Washington, 1917 | image1 = SeattleWestlake Square Comfort Station Seattle frontage 05.jpg | alt1 = Large bathroom with chairs and a free-standing radiator, lit by flat skylights | caption1 = A bathroom lit by vault lights | image2 = SeattleWestlake Square Comfort Station Seattle frontage 01.jpg | alt2 = A transport station with benches under a roof in the middle of a city square inset with inconspicuous rectangles of vault lights | caption2 = The outside, showing the same vault lights from above (dark rectangles) }}
Sidewalk prisms are a method of daylighting basements, and are able to serve as a sole source of illumination during the day. At night, lighting in the basements beneath produces a glowing sidewalk.<ref name=victoria /> Vault lights may be used to make subterranean space useful.<ref name=recon /> They are more common in city centers, dense, high-rent areas where space is valuable.<ref name=recon />
Historically, landlords took an interest in improving not only the floor area ratio, but the amount of space that was naturally lit, on the grounds that this was profitable.<ref name= handbook /> Occupiers valued daylight not only as a way of saving on artificial lighting costs, which were higher historically, but also as a way to let premises remain cooler in summer, and a way to save on ventilation costs, if using gas lighting rather than arc lamps or early incandescent lights.<ref name= handbook />
Pavement lights and related products were historically marketed as a way of saving on artificial lighting costs and making space more usable and pleasant.<ref name=handbook /> Modern studies of similar daylighting technology provide evidence for those claims.<ref name=DoD />
Vault lights also are used in floors under glass roofs, for example in Budapest's historic {{interlanguage link|Párizsi udvar|hu}}<ref name=Parizi /> and New York's mostly-demolished old Pennsylvania Station {{see below|{{section link||Current state and trends}}}}.<ref name=images_penn_station /> Vault lights also could be set into the basement floor, underneath other vault lights, creating a double-deck arrangement, which would light the subbasement.<ref name=NPS /> Manhole covers and coalhole covers with lighting elements were also made.<ref name=recon /> Some steps have vault lights set into the vertical stair risers.<ref name=stairs />
== History == A basement that extends below a sidewalk or pavement is called an areaway,<ref name=recon /> a vaulted sidewalk,<ref name=replacing_structure /> or a hollow sidewalk.<ref name=sacramento /> In some cities, these areaways were created by the raising of the street level to combat floods, and in some cases they form, an often now-abandoned, tunnel network.<ref name=statesman /><ref name=sacramento /><ref name=chicagotribune /> To light these spaces, sidewalks incorporated gratings, which were a trip hazard and let water and street dirt as well as light into the basement. Replacing the open gratings with glass was an obvious improvement.<ref name=glassian />
=== Frames === [[File:Rockwell vaultlight colourized.png|thumb|upright=1.5|alt=A large circular glass lens with a flat top and a stepped domed bottom. The glass is purple, with the shade darkening towards the top. The glass is set in a wide and ornate circular frame engraved with a semi-geometric ring-of-roundels design that looks a bit Art Deco, although from 1834. |Rockwell vault light, with one large piece of glass<ref name=rockwell_patent />]] Sidewalk prisms developed from deck prisms, which were used to let light through the decks of ships. The earliest pavement light (Rockwell, 1834)<ref name=rockwell_patent /> used a single large round glass lens set in an iron frame. The large lens was directly exposed to traffic, and if the lens broke, a large hole was left in the pavement, which was potentially unsafe for pedestrians.<ref name=glassian /><ref name=hyatt_patent />
Thaddeus Hyatt corrected these faults with his "Hyatt light" of 1854.<ref name=hyatt_patent /> Many small lenses ("bull's-eyes") were set in a wrought-iron frame,<ref name=LuxferCat /><ref name=glassian /> (later cast iron),<ref name=hargreaves /> and the frame included raised nubs around each lens to improve traction in wet weather and to protect them from damage and wear. Even if all the lenses were broken out, the panel would still be safe to walk on.<ref name=glassian />
In the 1930s, London authorities ruled that glass sections could not be larger than 100 mm by 100 mm.<ref name=size /> Modern glass floors are made of laminated and toughened glass pavers, which can be substantially larger. They have an upper protective layer that can be replaced if it becomes chipped or cracked.<ref name=Campbell-Dollaghan /> The top surface of the pavers may also be chosen and treated to improve traction.<ref>{{cite web |author=WalkerGlass.com |url=http://walkerglass.com/products/anti-slip-glass/ |title=Anti-slip Glass | Walker Textures™ |publisher=Walkerglass.com |date= |accessdate=2017-11-12 |url-status=live |archiveurl=https://web.archive.org/web/20171022085047/http://walkerglass.com/products/anti-slip-glass/ |archivedate=2017-10-22 }}</ref>
[[File:Armored pavement light element.jpg|thumb|upright=0.8|alt=A shallow square of glass, surrounded by a metal rim, set in rebar-reinforced concrete. Cutaway view.|Armoured glass in concrete]] Wrought iron,<ref name=LuxferCat /><ref name=glassian /> cast iron,<ref name=hargreaves /> and stainless steel<ref name=stainless /> frames have all been used. Reinforced concrete slabs began to replace iron frames in the 1890s in New York. Benefits claimed included less condensation (due to the lower thermal conductivity)<ref name=Sweet1906 /> and a less slippery surface when wet.<ref name=NYT /> Concrete panels may be pre-cast or cast in-situ.<ref name=insitu /><ref name=sweet1915 /> {{Crossreference|selfref=n|(For process details, see {{section link||External links}}, below.)}}
Late concrete panels often were made with metal-framed "armored prisms", which were intended to prevent breakage and make replacing individual prisms easier. The glass is not cast into the concrete but caulked into the frame. Rather than chiselling out the old glass, the glass can be popped out of the frame.<ref name=sweet1927 />
Translucent concrete has also been proposed as a floor material.<ref name=translucent_concrete /> This would essentially make it a vault light with very small (fiberoptic) lighting elements. It also innately redirects the light from the angle of incidence to an angle ~parallel to the optical fibers (usually, perpendicular to the surface of the concrete).
=== Transparent elements === The transparent elements may be referred to as prisms or lenses, depending on shape, or as jewels.<ref name=glassian />
==== Glass color ==== thumb|upright=1.5|alt=Shallow purple glass squares with deep right-angled prisms hanging from them. They are coloured purple, with the shade intensifying towards the top.|Solarized pendant prisms, showing a gradient in the solarization. The glass in many old pavement lights is now either purple or straw-colored. This is a side-effect of the manufacturing process. Pure silica glass is transparent, but older glass manufacture often used silica from sand, which contains iron and other impurities.<ref name=solarized/> Iron produces a greenish tint in the finished glass. To remove this effect, a "decolorizer" such as manganese dioxide ("glassmakers' soap") was added during the manufacture of the glass.
When exposed to ultraviolet light, the manganese slowly "solarizes", turning purple,<ref name=solarized/> which is why many existing sidewalk prisms are now purple.<ref name=victoria /> WWI increased demand for manganese in the US and cut off the supply of high-grade ore from Germany,<ref name=USGS /> so selenium dioxide was used as a decolorizer instead.<ref name=glassian_purple/> Selenium also solarizes, but to a straw color.<ref name=solarized/>
Replacement glass that has been tinted purple deliberately, in order to match the current colour, has been used in some historic restoration projects.<ref name=seattle/>
==== Glass shape ==== {{main|Prism lighting}} {{multiple image | width = | footer = | image1 = Scatter.gif | alt1 = A wedge of glass, in cross-section a right-angled triangle hung from the shortest side, with light passing downwards through the shortest side, hitting the hypotenuse, and bouncing out near-horizontally from the third side. The top of the wedge has ridges for setting it into a frame, and some of the light misses the wedge and continues downwards. | caption1 = Total internal reflection in a pendant prism | image2 = Multi&3-way.jpg | alt2 = Two black-rimmed squares of glass. Above, one with rows of identical small prism ridges. Below, one with three pendants like those in the last image, but increasing successively in size. | caption2 = Lenses with multiple rows of pendant prisms. Above, identical prisms; below, three dissimilar prisms sizes, for light dispersion. These lenses are armoured with malleable plastic | image3 = 3wayray.gif | caption3 = Ray diagram of the three dissimilar prisms sizes, designed to avoid blocking each other's light. Each prism can also send the light in a slightly different direction for more diffuse lighting. | alt3 = Like image one, but the three different-sized prisms send the outgoing light off on parallel, not overlapping, courses. }} In 1871 London, Hayward Brothers patented their "semi-prism": changing the shape of the glass by adding pendant prisms to the underside reflects the light sideways, allowing it to light the area under the main building. The pendant shapes were right-angle ("half") prisms, which reflected all incoming light sideways.<ref name=glassian /> The horizontal ridges protruding from the top of the prism let it be set into an opening in an iron or cement grating.
Some cast glass pendant prisms have flat portions to shed light directly below, as well as throwing it sideways under the main body of the building (see image). Some prisms were made with multiple pendant prisms, either as a Fresnel-lens-like sheet of identical prisms ("multi") or a sheet of dissimilar prisms that could distribute the light ("three-way" etc.).<ref name=shapes />
The precise angles at which the prisms refracted or reflected light was important. An installation would generally consist of multiple different prescriptions of prism, chosen either by an on-site expert contractor or by a layman using standard algorithms.<ref name=handbook /> This also would diffuse the light somewhat, as would the rough glass surfaces (the lenses are translucent, not transparent).
Larger castings are more expensive, not only because they use more glass, but because they take longer to cool.<ref name=annealing /> Modern glass floors use laminate sheet glass some centimeters (more than an inch) thick. It often is transparent.<ref name=Campbell-Dollaghan /> {{Clear}}
==== Non-glass translucent materials ==== Synthetic resin composites (such as fiberglass), as well as plastics such as Lexan, have been proposed to replace missing prism lights.<ref name=daily_astorian /> Translucent decking panels made of fiberglass are often used for balconies which would otherwise shade the windows below them.<ref name=translucent_decking>{{cite web |url=http://frpresource.com/2017/globalgridtranslucentdecking/ |title=GLOBALGRID™ Translucent Decking |publisher=Frpresource.com |accessdate=12 November 2017 |url-status=live |archiveurl=https://web.archive.org/web/20171113112902/http://frpresource.com/2017/globalgridtranslucentdecking/ |archivedate=13 November 2017 }}</ref> Peel-and-stick prism films recently have come on the market, with acrylic micro-prisms that internally reflect light somewhat like glass pendant prisms.<ref name=DoD /><ref name=OOtM /><ref name=TIR>{{cite web |url=https://sweets.construction.com/swts_content_files/154130/2263001.pdf |title=SerraGlaze Q&A |publisher=Sweet's Construction Catalog |accessdate=16 November 2017 |url-status=live |archiveurl=https://web.archive.org/web/20171116084258/https://sweets.construction.com/swts_content_files/154130/2263001.pdf |archivedate=16 November 2017 }}</ref>
=== Structure === <gallery mode="packed" heights="225"> File:Lucidux daylighting.gif|alt=Diagram of prisms in a pavement bending light to hit a wall of glass prims lying directly under and in line with the basement wall, which bend the light further to the horizontal|Two-stage refraction system for basement lighting; prism wall below center, shop above left. Note I-beam and masonry wall. File:Prism salesroom.gif|alt=A brightly-lit room with the inside edge lined with carrell desks. The ceiling is made of pendant prisms, supported by a very unobtrusive frame (which is in turn supported at wide intervals by slender diagonal braces from the walls). The wall over the desks is made of prism tiles.|The same system used to light a salesroom inside a hollow sidewalk; prism wall is on the right File:Daylit basement 112 state st.jpg|alt=A black-and-white photo of an unfurnished basement, horizontally lit with diffuse light. It has a pale coffered ceiling, with thickish round pillars supporting the intersections of the beams. The lower half of both pillars and walls is covered with dark wood panelling. The bare floor is pale grey.|A basement daylit by sidewalk prisms (prisms out-of-shot to the left) </gallery>
In some cases, a second vertical curtain of prisms was installed under the building sill.<ref name=LuxferCat /> These were analogous to the prism transoms used over above-ground windows and doors. The light could be bent in two stages and used to daylight the whole basement.<ref name=LuxferCat />
The areaway under a sidewalk light usually has a masonry wall separating it from the soil under the street, although it may extend partly under the street. Support for the vault light frames varies. Steel cross-beams supported by columns are common in older buildings; metal decks are common in newer ones.<ref name=replacing_structure />
== Current state and trends == {{multiple image | width = 250 | direction = vertical | image1 = NYP LOC5.jpg | alt1 = Large high-ceilinged space with round iron arches, covered in glass-dome skylights, floored with vault lights, clock central in foreground. | caption1 = The 1910 Pennsylvania Station Concourse in 1963, roofed with glass-dome skylights, floored with vault lights | image2 = Penn NY original floor.jpg | alt2 = View of the underside of the vault-light floor, supported by tapered concrete beams | caption2 = View up from track level, 2015; the vault lights are present, but concreted over }}
=== Manufacture, maintenance, and repair === Some modern pavement lights are quite different from historic ones,<ref name=Campbell-Dollaghan /><ref name=glassian /> so restoration and replacement may use different techniques and parts.
A few companies now manufacture and sell vault lights, either as glass-only, prefab panels, or installation.<ref name=recon /><ref name=current /> Construction methods and prices vary widely.<ref name=current /> Historically, glass lenses were standardized by each manufacturer; some modern manufacturers produce standardized prisms.<ref name=handbook /><ref name=recon /><ref name=hargreaves /> Some firms also supply replacement glass castings to order.<ref name=current /> Cost varies greatly; shapes needing complicated articulated moulds are more expensive.<ref name=recon />
Modern caulking materials are used for caulking in replacement glass. Broken and damaged frames can be patched, re-welded,<ref name=NPS /> or re-cast.<ref name=NPS /><ref name=hargreaves /> Generally speaking, restoration requires only simple tools and technology.<ref name=NPS />
Promptly repairing sidewalk cracks, and avoiding de-icers that will corrode metal, helps keep the supporting structure dry and in good repair.<ref name=replacing_structure /> Keeping a sidewalk light watertight does not cost much in time or materials.<ref name=NPS /> Vaults generally last many decades,<ref name=replacing_structure /> and many extant vaults are more than a century old.<ref name=recon />
=== Reuse and preservation === Despite their reusability and repairability, old panels often are landfilled.<ref name=demolition /><ref name=victoria /><ref name=recon /> However, the city of Victoria, Canada is stockpiling removed pavement light panels for future restoration projects.<ref name=victoria /><ref name=recon /> Often, individual broken sidewalk prisms are not replaced, but instead, the opening is filled with concrete or other opaque materials,<ref name=recon /> such as metal, wood, and asphalt.<ref name=NPS />
When a building is renovated, vault lights may be removed or concreted over. For instance, the floor of New York's mostly-demolished old Pennsylvania Station was made of vault lights, to let light through the concourse floor onto the platforms.<ref name=images_penn_station /> The undersides of the lights can still be seen, but the tops have been concreted over (see images).<ref>Photo, 2015</ref>
While some cities have preservation measures for vault lights, others actively remove them and fill areaways.<ref name=recon /> Sometimes the outside appearance of the lights is retained while filling the areaway and setting the lights in a concrete pad, removing their daylighting function.<ref name=NPS /> Some areaways are "mothballed"; that is, filled with gravel that could later be removed.<ref name=recon />
Areaways are used in some cities as a convenient place to run utilities, which may make the cities reluctant to give areaways legal protection.<ref name=recon /> In some cases, utility construction leads to areaways being filled.<ref name=statesman />
=== Load-bearing strength === The load-bearing strength of vault lights varies widely with span, construction, and state of repair. Some damaged vaults may not be able to support a fire engine,<ref name=vanheritage /> which a sidewalk vault in sound condition should be able to do.<ref name=replacing_structure /> Many jurisdictions do not have regulations on the load-bearing capacity of pavement lights, and manufacturers may develop their own loading standards, in compliance with local fire department regulations. The load-bearing capacity of pavement lights can be tested, and lights can be designed and built to specific load-bearing capacities.<ref name=loading>{{cite web |title=Loading – Cast Iron Pavement Lights |url=http://castironpavementlights.com/technical-loading/ |accessdate=5 December 2019}}</ref>
Damp areaways may corrode the steel load-bearing elements supporting the pavement roof. Moisture may come from leakage from above or from groundwater from below.<ref name=recon />
=== Current installations === thumb|alt=Two people in work gloves carefully transferring a heavy panel of pavement lights from a small flat-bed truck to a pile of similar panels, separated by wooden spacers. The pile is on the outside edge of the sidewalk, and pedestrians pass them on the inside. The panel has a black metal frame and round white lenses. It is about 1.5x0.5m (possibly 2x4 feet)|Restored vault lights being re-installed on Broadway in New York City
*'''Amsterdam''', The Netherlands, has vault lights, some of which have been documented by the Netherlands Department for Conservation.<ref>{{cite web |url=http://www.glassian.org/Prism/Gallery/Amsterdam/index.html |title=Vault Lights in Amsterdam, the Netherlands |publisher=glassian |accessdate=12 November 2017 |url-status=live |archiveurl=https://web.archive.org/web/20161115085219/http://glassian.org/Prism/Gallery/Amsterdam/index.html |archivedate=15 November 2016 }}</ref> *'''Astoria''', Oregon, has a community program for restoring vault lights, funded by the Astoria Downtown Historic District Association. A volunteer plan to replace broken glass with squares of Lexan, topped with resin embedded with glass teardrops, was prevented by legislation.<ref name=daily_astorian /> *'''Budapest''', Hungary, has vault lights in one of its tourist sites, the Art Deco-period {{interlanguage link|Párizsi udvar|hu}} mall on Ferenciek tere (Square of the Franciscans). The mall has unusual, decorative pavement lights let into its polychrome tile floor, to allow light from the glass dome skylights into the basement level. There also are vault lights in other locations, such as in the old post office building.<ref name=Parizi>{{cite web |url=http://www.glassian.org/Prism/Gallery/Budapest/index.html |title=Vault Lights in Budapest, Hungary |publisher=glassian |accessdate=12 November 2017 |url-status=live |archiveurl=https://web.archive.org/web/20161112164021/http://glassian.org/Prism/Gallery/Budapest/index.html |archivedate=12 November 2016 }}</ref> *'''Chicago''', Illinois, has extremely extensive sidewalk vaults, but many of them do not have vault lights. There is no inventory of them. The city is filling in all vaults, as some are structurally unsound.<ref name=chicagotribune /> See also the raising of Chicago. *'''Deadwood''', South Dakota, funded a major restoration and maintenance project for vault lights in approximately 2000.<ref name=recon /> *'''Dublin''', Ireland has many vault lights.<ref>{{cite web |url=http://www.glassian.org/Prism/Gallery/Dublin/index.html |title=Vault Lights in Dublin, Ireland |publisher=glassian |accessdate=12 November 2017 |url-status=live |archiveurl=https://web.archive.org/web/20170311133101/http://glassian.org/Prism/Gallery/Dublin/index.html |archivedate=11 March 2017 }}</ref> *'''Dunedin''', New Zealand has well-preserved Luxfer and Hayward Brothers vault lights.<ref>{{cite web |url=http://www.glassian.org/Prism/Gallery/Dunedin/index.html |title=Vault Lights in Dunedin, New Zealand |publisher=glassian |accessdate=12 November 2017 |url-status=live |archiveurl=https://web.archive.org/web/20160401095655/http://glassian.org/Prism/Gallery/Dunedin/index.html |archivedate=1 April 2016 }}</ref> *'''London''', England has many vault lights, many made by the Hayward Brothers.<ref>{{cite web |url=http://faded-london.blogspot.ca/2009/01/lightwells-and-their-variants.html |title=Faded London: Lightwells and their variants |publisher=Faded-london.blogspot.ca |date=1 January 2009 |accessdate=12 November 2017 |url-status=live |archiveurl=https://web.archive.org/web/20171023063624/http://faded-london.blogspot.ca/2009/01/lightwells-and-their-variants.html |archivedate=23 October 2017 }}</ref> Historic preservation legislation encourages a market in new pavement lights. *'''New York City''' has large numbers of vault lights, mostly in the SoHo district. More than half of the subway stations originally had vault lights, but these had mostly been blocked off. Installing and restoring vault lights has become part of modern construction practices.<ref name=NYT /> The city government has no policies or records about vault lights.<ref name=recon /> *'''Philadelphia''', Pennsylvania has numerous vault lights, some of them locally manufactured.<ref name=philadelphia /> *'''Portland''', Oregon has prisms at several locations.<ref>{{cite web|url=https://cyclotram.blogspot.ca/2006/11/like-amethysts-beneath-my-feet.html|title=cyclotram: like amethysts beneath my feet|website=cyclotram|date=November 2006}}</ref> It has no preservation project for its prisms, however, and fills those that break with concrete.<ref name=recon /> There is some local opposition to the policy.<ref>{{cite web|url=http://historicpreservationclub.blogspot.ca/search/label/Purple%20Prism%20Glass|title=Sidewalks Part Five: Purple Glass Prisms Hidden in plain site{{sic|nolink=y}}|website=Historic Preservation Club|date=22 January 2012}}</ref> See also Portland Underground. *'''Pretoria''', South Africa has Hayward vault lights.<ref>{{cite web |url=http://www.glassian.org/Prism/Gallery/Pretoria/index.html |title=Vault Lights in Pretoria, South Africa |publisher=glassian |accessdate=12 November 2017 |url-status=live |archiveurl=https://web.archive.org/web/20160401094542/http://glassian.org/Prism/Gallery/Pretoria/index.html |archivedate=1 April 2016 }}</ref> *'''Sacramento''', California has "hollow sidewalks", which originated when the city raised its street level to combat floods; some of these spaces are lit by vault lights. There are many stories told about these areas.<ref name=sacramento /> *'''Salem''', Oregon has an extensive tunnel network with vault lights.<ref name=opb /> Historians have found a mural-painted grocery drop,<ref name=oregonlive /> a disco, a swimming pool, a firing range, opium dens, and bordellos in the tunnels.<ref name=statesman /> Guided tours are sometimes conducted in the tunnels.<ref name="statesman2017">{{cite web|url=https://www.statesmanjournal.com/story/news/holdingcourt/2017/06/10/salems-underground-history-display/386118001/|publisher=Statesman Journal|title=Salem's underground history on display|accessdate=16 October 2018}}</ref><ref name=opb/> The Go Downtown Salem! Board welcomed the idea of regular underground tours.<ref name=oregonlive /> Many of the tunnels have been filled during sewer construction.<ref name=statesman /> *'''San Diego''', California has sixteen-sided pavement jewels of the "Searchlight" brand.<ref name=San_Diego /> *'''San Francisco''' evaluates the lights as having little historic value, and as a safety hazard for pedestrians.<ref>{{Cite web |last=Jones |first=Shayne |date=2023-06-01 |title=These overlooked SF artifacts could completely disappear one day |url=https://www.sfgate.com/local/article/san-francisco-sidewalk-vault-lights-history-18121989.php |access-date=2023-06-09 |website=SFGATE |language=en-US}}</ref> Most of the lights have been removed.<ref name=recon /> *'''Saskatoon''', Saskatchewan has had sidewalk prisms. They have been used in music videos, and a Facebook group fought to save them.<ref name="starpheonix" /> They were scheduled to be infilled in 2015.<ref name=saskimage />
[[File:Seattle Underground - Skylights from underneath current street level.JPG|thumb|upright|right|alt=A dingy panel of pale purple squares set deeply into a shallow yellow brick arch. People with a light by an arched doorway leading to a further gallery in the background. Pipes run through the picture.|Disused sidewalk prisms lighting the abandoned Seattle Underground]] *'''Seattle''', Washington raised its street level, by up to 22 feet in some places, in the aftermath of the Great Seattle Fire of 1889.<ref name=recon /> Previously, the Pioneer Square area had flooded tidally.<ref name=recon /> Seattle replaced some of its sidewalk vault lights in Pioneer Square with new pre-purpled ones in 2002. Seattle runs tourist trips through its underground.<ref name=seattle /> *'''Tijuana''', Mexico has armoured unsolarized vault lights in the 1919 Casa de la Cultura.<ref name=Tijuana /> *'''Toronto''', Ontario once had many vault lights, but the last known remaining example were in front of the shops at 2869 Dundas Street West (near Keele) until 2011.<ref name=toronto /> *'''Vancouver''', British Columbia has an unofficial policy of requiring any applicants for development permits to fill in areaways,<ref name=vanheritage /><ref name=recon /> although some have been paved over or made sufficiently load-bearing to support a fire engine.<ref name=vanalogue_gallery /> Some of the remaining areaways have restaurants built into them.<ref name=scout /> A walking map of the sidewalk prisms has been produced.<ref name=map /><ref name=vanalogue_gallery /> There are ~130 remaining areaways, the records of which are not digitised, and no measures exist to promote their preservation.<ref name=recon /> *'''Victoria''', British Columbia has more than eleven thousand sidewalk prisms in seven locations (as of 2006), including an underground gallery running around an entire block outside the Yarrow Building. More than 670 of the prisms are missing or filled with concrete.<ref name=recon /> Sidewalk prisms have been heritage-registered since 1990. Originally, there were hundreds of thousands of prisms. The city has some panels in storage for restoration, but is having difficulty finding a glass supplier. There are city plans to light the galleries below at night, creating glowing purple sidewalks in the downtown core.<ref name=victoria /> While they are protected, there is no funding for the preservation of sidewalk prisms.<ref name=recon /> {{Clear}}
== Gallery == <gallery mode="packed"> File:Budapešť, Belváros, Váci út, Parisi udvar.JPG|alt=A rather Gothick 18th-century indoor mall, with high round-arched ceilings and ornate pendants from the roof.|The {{interlanguage link|Párizsi udvar|hu}} in Budapest, with pavement lights let into its polychrome tile floor to allow light from the glass dome skylights into the basement level ([http://www.glassian.org/Prism/Gallery/Budapest/index.html details]) File:Toronto BCE Place at night.jpg|alt=A towering metal gridwork catenary arch forms a gallery over a shiny concrete concourse inset with glowing grids of glass. Beyond the arch, city lights of tall buildings are visible. A four-story historic stone building stands to the left; a plain modern building rises out of sight to the right.|The Brookfield Place in Toronto, Canada, at night File:Luik Gare Liège-Guillemins.jpg|alt=A close-up of a similar grid of glass squares, slightly blueish glass with a wavy lower surface, in full sunlight.|A similar floor by day at the Liège-Guillemins railway station in Belgium File:Michigan State Capitol Glass Bock Floor.jpg|alt=A cylindrical room with a glass floor surrounded by two higher stories of circular balconies with ornate bulbous balusters. The room is lit by incandescent lights.|The floor of the rotunda of the Michigan State Capitol has a wrought-iron frame shaped to give the illusion of a bowl shape from above ([http://capitol.michigan.gov/CapitolBuilding from below]) File:Linares - Museo Arqueológico 7.jpg|In a glass-covered courtyard in the Museo Arqueológico de Linares File:GFRP Translucent deck panels.jpg|alt=Bridge at night with multicoloured LED lights lighting the bridge from below; each successive panel is lit in a different colour.|Translucent fiberglass deck of a bridge in Lleida, Spain, lit from below File:GLOBALGRID_translucent_decking01.jpg|alt=Pine decking with a panel of fiberglass showing a fine grid set in a mitered pine frame. The fiberglass is slightly blue-green, and sits squarely in front of the glass doors to the house.|Translucent fiberglass pavement light built into a balcony, allowing sunlight into the area under the deck File:Luxfer sidewalk.gif|alt=A bright grid of glass with deep cross beams and shallow along-sidewalk beams.|An area under a sidewalk, 1915, showing clear glass File:Multi-Prism_vault_lights_from_below.jpg|alt=View from below of small circular panes of translucent lavender glass, deeply set in a coffered grid. Each circle has three parallel pendant-prism ridges.|Purple-solarized vault lights from ca. 1880, Etna, California File:Chamberlin Hotel-5.jpg|Purpled and patched vault lights outside the historic Chamberlin Hotel in Portland, Oregon. Grouting has been used to re-seal cracked glass jewels. File:Pavement in Worcester Street, Wolverhampton - geograph.org.uk - 1670792.jpg|A pavement light set into the pavement outside a store (close-up) File:BurlingtonHousePavementWindow.jpg|A pavement light outside Burlington House in London, England File:Armored panels.jpg|Armoured vault lights installed in the sidewalk outside a store File:1886 diagram varied lenses.gif|Cross-section of a pavement light panel, showing alternating lenses and prisms File:Glass sidewalk pavement light, Geneva NY.jpg|alt=Square clear-glass pendant prisms.|Pavement lights in Geneva, New York (flash version). Large pendant right-angle prisms as in previous image. File:GLOBALGRID translucent decking10.jpg|Translucent fiberglass pavement light panel, close-up File:Sidewalk, R. Estudos - University of Coimbra - Coimbra, Portugal - DSC09050.jpg|In Portuguese pavement File:Ping Shan Tin Shui Wai Glass floor Terrace 2016.jpg|On a terrace File:Book Shelves (8712833696).jpg|In a library, glass above and below (close-up) </gallery>
.jpg){kind=link}
== See also == * Anidolic lighting * Daylighting * Deck prism * Prism lighting * Thaddeus Hyatt – made the money he spent fighting slavery with ''Hyatt lights'', innovative small-paned lights in cast-iron frames<ref name=glassian /> * Underground city (vault lights are used to light some)<ref name=campus_tunnels />
== References == <references>
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<ref name=glassian>{{Citation |last = Macky |first = Ian |title = Prism glass |website = Glassian |url = http://www.glassian.org/Prism/ |url-status = live |archiveurl = https://web.archive.org/web/20170929092533/https://www.glassian.org/Prism/ |archivedate = 29 September 2017 }}</ref>
<ref name=glassian_gallery>{{Citation |last = Macky |first = Ian |title = Prism glass, gallery[of installations worldwide] |website = Glassian |url = http://www.glassian.org/Prism/ |url-status = live |archiveurl = https://web.archive.org/web/20090321164739/http://glassian.org/Prism/ |archivedate = 21 March 2009 }}</ref>
<ref name=glassian_purple> {{cite web|url=https://glassian.org/Gallery/purple.html |title= Purple Insulator Gallery |publisher=glassian |accessdate=27 January 2018}} </ref>
<ref name=stairs> {{cite web|url=http://glassian.org/Prism/Gallery/Chicago/index.html |title=Vault Lights in Chicago, Illinois |publisher=glassian |date=2 April 2003 |accessdate=3 December 2017}} </ref>
<ref name=demolition> {{cite web|url=http://glassian.org/Prism/Gallery/Stockton/index.html |title=Vault Lights in Stockton, California |publisher=glassian |date= |accessdate=3 December 2017}} </ref>
<ref name=campus_tunnels>{{cite web|url=http://glassian.org/Prism/Gallery/DevilsLake/index.html |title=Vault Lights at the NDSD in Devils Lake, North Dakota |publisher=glassian |date= |accessdate=3 December 2017}}</ref>
<ref name=translucent_concrete>{{cite web|url=http://illumin.usc.edu/245/translucent-concrete-an-emerging-material/ |title=Translucent Concrete: An Emerging Material |work=Illumin |publisher=The Engineering Writing Program at the University of Southern California Viterbi School of Engineering|volume=18 |issue=2|date=3 December 2017 |accessdate=3 December 2017}}</ref>
<ref name=images_penn_station> {{Citation |last = Macky |first = Ian |title = Vault Lights in Penn Station, NYC |website = Glassian |url = http://www.glassian.org/Prism/Gallery/NewYork/penn_station.html |url-status = live |archiveurl = https://web.archive.org/web/20160512165619/http://glassian.org/Prism/Gallery/NewYork/penn_station.html |archivedate = 12 May 2016 }}</ref>
<ref name=OOtM>[http://www.archlighting.com/products/daylighting-and-solar-control/object-of-the-moment-3m-daylight-redirecting-film-by-3m_s Object of the Moment: 3M Daylight Redirecting Film by 3M] {{webarchive|url=https://web.archive.org/web/20170320034936/http://www.archlighting.com/products/daylighting-and-solar-control/object-of-the-moment-3m-daylight-redirecting-film-by-3m_s |date=20 March 2017 }}, by Selin Ashaboglu, 2 March 2017</ref>
<ref name=annealing>{{Citation |author = Bullseye Glass Co. |title = Annealing Thick Slabs |url = https://www.bullseyeglass.com/methods-ideas/annealing-thick-slabs.html |url-status = live |archiveurl = https://web.archive.org/web/20171112021517/https://www.bullseyeglass.com/methods-ideas/annealing-thick-slabs.html |archivedate = 12 November 2017 }}</ref>
<ref name=current>{{Citation |last = Macky |first = Ian |title = Current Manufacturers |website = Glassian |url = http://glassian.org/Prism/current.html |url-status = live |archiveurl = https://web.archive.org/web/20171010104640/http://glassian.org/Prism/current.html |archivedate = 10 October 2017 }}</ref>
<ref name=handbook>{{Citation |editor=Henry Crew |editor2=Olin H. Basquin |title = Pocket Hand-book of Electro-glazed Luxfer Prisms containing useful information and tables relating to their use For Architects, Engineers and Builders. |year = 1898 |website = Glassian |url = http://glassian.org/Prism/Luxfer/Handbook/page1.html |url-status = live |archiveurl = https://web.archive.org/web/20160310000629/http://www.glassian.org/Prism/Luxfer/Handbook/page1.html |archivedate = 10 March 2016 }}</ref>
<ref name=hargreaves>{{Citation |author = Hargreaves Foundry |title = Replacement of Traditional Pavement Lights |date = 19 November 2014 |url = http://www.hargreavesfoundry.co.uk/blog/blogview/47/replacement-of-traditional-pavement-lights |url-status = live |archiveurl = https://web.archive.org/web/20171007120149/http://www.hargreavesfoundry.co.uk/blog/blogview/47/replacement-of-traditional-pavement-lights |archivedate = 7 October 2017 }}</ref>
<ref name=DoD>{{cite report |mode=cs1 |last=Padiyath |first=Raghunath |title=Daylight Redirecting Window Films |access-date=9 October 2017 |date=2013 |id=EW-201014 |url=https://www.serdp-estcp.org/Program-Areas/Energy-and-Water/Energy/Conservation-and-Efficiency/EW-201014 |website=serdp-estcp.org |url-status=live |archive-url=https://web.archive.org/web/20170929092911/https://www.serdp-estcp.org/Program-Areas/Energy-and-Water/Energy/Conservation-and-Efficiency/EW-201014 |archive-date=29 September 2017}}</ref>
<ref name=LuxferCat>[http://glassian.org/Prism/Luxfer/CA/Catalogue/page25.html The Luxfer Prism Co., Ltd. of Canada, Catalogue.] {{webarchive|url=https://web.archive.org/web/20160914211930/http://glassian.org/Prism/Luxfer/CA/Catalogue/page25.html |date=14 September 2016 }}</ref>
<ref name=philadelphia>{{Citation |last = Robinson |first = Sam |title = Diffused Down Below: Philadelphia's Lost Vault Lights |work = Hiddencity Philadelphia |date = 19 June 2013 |url = http://hiddencityphila.org/2013/06/diffused-down-below-philadelphias-lost-vault-lights/ |url-status = live |archiveurl = https://web.archive.org/web/20171023063818/http://hiddencityphila.org/2013/06/diffused-down-below-philadelphias-lost-vault-lights/ |archivedate = 23 October 2017 }}</ref>
<ref name=seattle>[http://seattleglassonline.blogspot.ca/2010/05/abj-seattle-glass-online-on-temporary.html Minutes of city meetings on sidewalk prisms] {{webarchive|url=https://web.archive.org/web/20171004085836/http://seattleglassonline.blogspot.ca/2010/05/abj-seattle-glass-online-on-temporary.html |date=4 October 2017 }} in Seattle, USA, and Victoria, Canada</ref>
<ref name=recon>{{Citation |title = Seattle Prism Light Reconnaissance Study |author = Marie Wong |publisher=Institute for Public Service, Seattle University |display-authors=etal |year = 2011 |url = http://allianceforpioneersquare.org/wp/wp-content/uploads/2011/12/Seattle-Prism-Light-Reconnaissance-Study.pdf |url-status = live |archiveurl = https://web.archive.org/web/20160327142938/http://allianceforpioneersquare.org/wp/wp-content/uploads/2011/12/Seattle-Prism-Light-Reconnaissance-Study.pdf |archivedate = 27 March 2016 }}</ref>
<ref name=chicagotribune>{{Citation |last = Lord |first = Steve |title = Vault project shines light on underground Aurora |newspaper = The Chicago Tribune |date = 29 September 2017 |url = http://www.chicagotribune.com/suburbs/aurora-beacon-news/news/ct-abn-aurora-vaults-st-0928-20170929-story.html |archive-url = https://web.archive.org/web/20171028094059/http://www.chicagotribune.com/suburbs/aurora-beacon-news/news/ct-abn-aurora-vaults-st-0928-20170929-story.html |archive-date = 28 October 2017 |url-status = live }}</ref>
<ref name=daily_astorian>{{Citation |last = Stratton |first = Edward |title = Let the light in |newspaper = The Daily Astorian |date = 7 December 2015 |url = http://www.dailyastorian.com/friday-extra/20151207/let-the-light-in |archive-url = https://web.archive.org/web/20171009042413/http://www.dailyastorian.com/friday-extra/20151207/let-the-light-in |archive-date = 9 October 2017 |url-status = live }}</ref>
<ref name=sacramento>{{Citation |last = Garvin |first = Cosmo |title = The past below |newspaper = Sacramento Newsreview |date = 17 July 2003 |url = http://www.newsreview.com/sacramento/past-below/content?oid=15424 |archive-url = https://web.archive.org/web/20140208020116/http://www.newsreview.com/sacramento/past-below/content?oid=15424 |archive-date = 8 February 2014 |url-status = live }}</ref>
<ref name=opb>{{cite web|author=Chris Lehman |url=https://www.opb.org/news/article/historians-explore-salems-underground/ |title=Historians Explore Salem's Underground |publisher=OPB |date= |accessdate=3 December 2017}}</ref>
<ref name=oregonlive>{{cite web|url=http://www.oregonlive.com/pacific-northwest-news/index.ssf/2010/10/historians_explore_tunnels_beneath_salem.html |title=Historians explore tunnels beneath Salem |publisher=OregonLive.com |date=20 October 2010 |accessdate=3 December 2017}}</ref>
<ref name=statesman>{{cite web|url=http://www.statesmanjournal.com/story/opinion/columnists/capi-lynn/2015/01/31/john-ritter-salem-history/22627533/?from=global&sessionKey=&autologin= |title=From opium dens to bordellos, historian unearths Salem's past |publisher=Statesmanjournal.com |date=30 January 2015 |accessdate=3 December 2017}}</ref>
<ref name=San_Diego>{{cite web|url=http://glassian.org/Prism/Gallery/SanDiego/index.html |title=Vault Lights in San Diego, California |author=Ian Macky |publisher=glassian |date= |accessdate=3 December 2017}}</ref>
<ref name=Tijuana>{{cite web|url=http://glassian.org/Prism/Gallery/Tijuana/index.html |title=Vault Lights in Tijuana, Mexico |author=Ian Macky |publisher=glassian |date= |accessdate=3 December 2017}}</ref>
<ref name=Sweet1906>[http://glassian.org/Prism/Luxfer/Sweet06/page267.html 1906 Sweet's Indexed Catalog of Building Construction] {{webarchive|url=https://web.archive.org/web/20160914200808/http://glassian.org/Prism/Luxfer/Sweet06/page267.html |date=14 September 2016 }}, page 267</ref>
<ref name=sweet1915>[http://glassian.org/Prism/Luxfer/Sweet15/page174.html 1915 Sweet's Indexed Catalog of Building Construction] {{webarchive|url=https://web.archive.org/web/20160914223839/http://glassian.org/Prism/Luxfer/Sweet15/page174.html |date=14 September 2016 }}, page 174</ref>
<ref name=sweet1927>[http://www.glassian.org/Prism/3WayLux/Sweet27-28/A387.html 1927–1928 Sweet's Indexed Catalog of Building Construction] {{webarchive|url=https://web.archive.org/web/20160401095800/http://glassian.org/Prism/3WayLux/Sweet27-28/A387.html |date=1 April 2016 }}, page A387</ref>
<ref name=shapes>[http://glassian.org/Prism/3Way/14S/page2.html Vault Lighting and How It Is Secured] {{webarchive|url=https://web.archive.org/web/20160914214630/http://glassian.org/Prism/3Way/14S/page2.html |date=14 September 2016 }}, Catalog 14-S, American 3-Way Prism Company</ref>
<ref name=size>{{cite web |last1=Brassington |first1=Kevan |title=Precast concrete pavement lights |url=https://www.thenbs.com/knowledge/precast-concrete-pavement-lights |website=NBS |publisher=RIBA Enterprises Ltd |accessdate=7 December 2019 |date= 1 June 2013 |language=en}}</ref>
<ref name=insitu>[http://www.luxcrete.co.uk/pavement-lights/ Pavement Lights] {{webarchive|url=https://web.archive.org/web/20171007120157/http://www.luxcrete.co.uk/pavement-lights/ |date=7 October 2017 }}, Luxcrete Limited</ref>
<ref name=stainless>[https://surespancovers.com/product/pavevent/ Glazed Walk-on Floorlight Access] {{webarchive|url=https://web.archive.org/web/20171009092419/https://surespancovers.com/product/pavevent/ |date=2017-10-09 }}, Surespan</ref>
<ref name="starpheonix">{{Cite news| last = David Hutton| title = Group wants to save sidewalk prism lights| work = Saskatoon StarPhoenix| accessdate = 21 October 2017| date = 30 November 2011| url = https://thestarphoenix.com/news/local-news/group-wants-to-save-sidewalk-prism-lights| url-status = live| archiveurl = https://web.archive.org/web/20171022033652/http://thestarphoenix.com/news/local-news/group-wants-to-save-sidewalk-prism-lights| archivedate = 22 October 2017}}</ref>
<ref name=saskimage>{{cite web| title = Purple glass prisms inset in the sidewalk on 21st Street East in front of the Urban Oasis Tower are seen, Monday, April 13, 2015. Tunnels under the area are scheduled to be infilled.| author = Greg Pender, The StarPhoenix| date = 13 April 2015| accessdate = 21 October 2017| url = https://vancouversun.com/Purple+glass+prisms+inset+sidewalk+21st+Street+East+front+Urban+Oasis+Tower+seen+Monday+April+2015+Tunnels+under+area+scheduled+infilled/10969281/story.html| url-status = live| archiveurl = https://web.archive.org/web/20171022084837/http://www.vancouversun.com/Purple+glass+prisms+inset+sidewalk+21st+Street+East+front+Urban+Oasis+Tower+seen+Monday+April+2015+Tunnels+under+area+scheduled+infilled/10969281/story.html| archivedate = 22 October 2017}}</ref>
<ref name=toronto>{{Cite news| author = Matthew Blackett| title = Vault lights are more than sidewalk decor| work = Spacing Magazine| accessdate = 22 October 2017| date = 5 January 2010| url = http://spacing.ca/magazine/section/infrastructure-fetish/vault-lights-are-more-than-sidewalk-decor/| url-status = live| archiveurl = https://web.archive.org/web/20171023011631/http://spacing.ca/magazine/section/infrastructure-fetish/vault-lights-are-more-than-sidewalk-decor/| archivedate = 23 October 2017}}</ref>
<ref name=victoria>{{Citation |last1 = Ringuette |first1 = Janis |last2 = Ringuette |first2 = Norm |title = Walking Over History: Victoria's Historic Sidewalk Prisms |year = 2007 |url = http://www.islandnet.com/~jar/streetscapes/topics/prisms.htm |url-status = live |archiveurl = https://web.archive.org/web/20080509074924/http://www.islandnet.com/~jar/streetscapes/topics/prisms.htm |archivedate = 9 May 2008 }}</ref>
<ref name=replacing_structure>{{Citation | last1 = Varone | first1 = Stephen | last2 =Varsalona | first2 =Peter | title =Replacing a Sidewalk Vault | publisher = original publisher: Habitat Magazine at habitatmag.com; now rehosted by Rand Engineering and Architecture, DPC | work = Habitat Magazine | series = Ask The Engineer | date = October 2004 | url = https://randpc.com/ask/structural/replacing-sidewalk-vault/ | access-date = }}</ref>
<ref name=scout>{{Citation |last = Morrison |first = Andrew |title = The Purple Lights Of Our Ancient Basements |newspaper = Scout Vancouver |date = 19 October 2015 |url = http://scoutmagazine.ca/2015/10/19/1000-cool-things-about-vancouver-the-purple-illumination-of-ancient-basements/ |url-status = live |archiveurl = https://web.archive.org/web/20171004135444/http://scoutmagazine.ca/2015/10/19/1000-cool-things-about-vancouver-the-purple-illumination-of-ancient-basements/ |archivedate = 4 October 2017 }}</ref>
<ref name=solarized>{{Citation |title = Solarized glass |publisher = Corning Museum of Glass |date = 8 December 2011 |url = https://www.cmog.org/article/solarized-glass |url-status = live |archiveurl = https://web.archive.org/web/20171008130124/https://www.cmog.org/article/solarized-glass |archivedate = 8 October 2017 }}</ref>
<ref name=map>{{Citation |last = Knopp |first = Samantha |title = Purple City – A Little History of Vancouver's Vault Lights |publisher = Artists Walking Home Project |url = http://artistswalkinghome.ca/purple-city-a-little-history-of-vancouvers-vault-lights/ |url-status = live |archiveurl = https://web.archive.org/web/20171004085311/http://artistswalkinghome.ca/purple-city-a-little-history-of-vancouvers-vault-lights/ |archivedate = 4 October 2017 }}</ref>
<ref name=NPS>{{Citation |title = PRESERVATION Tech Notes: Repair and Rehabilitation of Historic Sidewalk Vault Lights, PTN 47 |publisher = National Park Service (U.S.A.) |date = November 2003 |issn = 0741-9023 |url = https://www.nps.gov/tps/how-to-preserve/tech-notes/Tech-Notes-Glass02.pdf |url-status = dead |archive-url = https://web.archive.org/web/20170506065254/https://www.nps.gov/tps/how-to-preserve/tech-notes/Tech-Notes-Glass02.pdf |archive-date = 6 May 2017 }}
'''NOTE''': colour versions of images available on Commons:Repair and Rehabilitation of Historic Sidewalk Vault Lights at 552-554 Broadway, New York City (2002) (URL formerly {{cite web |url=http://www.cr.nps.gov/hps/tps/technotes/ptn47/intro.htm |title=Technical Preservation Services, National Park Service |access-date=8 October 2017 |url-status=dead |archive-url=https://web.archive.org/web/20110425010929/http://www.cr.nps.gov/hps/tps/technotes/ptn47/intro.htm |archive-date=25 April 2011 }})</ref>
<ref name=USGS>{{Citation| title =Manganese statistics| series =Kelly, T.D., and Matos, G.R., comps., Historical statistics for mineral and material commodities in the United States: U.S. Geological Survey Data Series 140| publisher =U.S. Geological Survey| date =1 April 2014| url =https://minerals.usgs.gov/minerals/pubs/historical-statistics/ds140-manga.pdf| access-date =9 October 2017| url-status =live| archiveurl =https://web.archive.org/web/20170224171827/https://minerals.usgs.gov/minerals/pubs/historical-statistics/ds140-manga.pdf| archivedate =24 February 2017}}</ref>
<ref name=vanheritage>{{Citation |last = Murdy |first = Justine |title = The Dirt on Areaways |newspaper = Heritage Vancouver Newsletter |volume = 8 |number = 2 |date = February 1999 |url = http://www.heritagevancouver.org/pdf_newsletter/hvs-news-1999-full-screen.pdf |archive-url = https://web.archive.org/web/20160410193704/http://heritagevancouver.org/pdf_newsletter/hvs-news-1999-full-screen.pdf |archive-date = 10 April 2016 |url-status = live }}</ref>
<ref name=vanalogue_gallery>{{Citation |last = Hagemoen |first = Christine |title = Sidewalk prisms of Vancouver |publisher = Vanalogue |date = 13 April 2016 |url = https://vanalogue.wordpress.com/2016/04/14/sidewalk-prisms-of-vancouver/ |url-status = live |archiveurl = https://web.archive.org/web/20171004090119/https://vanalogue.wordpress.com/2016/04/14/sidewalk-prisms-of-vancouver/ |archivedate = 4 October 2017 }}</ref>
<ref name=rockwell_patent>{{cite patent |inventor-last = Rockwell |inventor-first = E. |inventorlink = |date = |issue-date = 8 March 1834 |title = [http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=X8,058 Rockwell, Vault cover] |country-code = US |description = |patent-number = X8,058 |url = http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=X8,058 |df = }} {{Webarchive|url=https://web.archive.org/web/20171008080250/http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=X8,058 |date=8 October 2017 }}</ref>
<ref name=hyatt_patent>{{cite patent |inventor-last = Hyatt |inventor-first = Thaddeus |inventorlink = |date = |issue-date = 19 September 1854 |title = [http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=11,695 Hyatt, Vault cover] |country-code = US |description = |patent-number = 11,695 |url = http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=11,695 |df = }}</ref>
<ref name=Campbell-Dollaghan>{{cite web|last1=Campbell-Dollaghan|first1=Kelsey|title=The Willis Tower's 103rd Floor Glass Skydeck Cracked Last Night|url=https://gizmodo.com/the-willis-towers-103rd-floor-glass-skydeck-cracked-las-1583211680|website=Gizmodo|publisher=Gizmodo.com|accessdate=4 June 2014|date=29 May 2014|url-status=live|archiveurl=https://web.archive.org/web/20140603073807/http://gizmodo.com/the-willis-towers-103rd-floor-glass-skydeck-cracked-las-1583211680|archivedate=3 June 2014}}</ref>
</references>
==External links== *[https://sidewalkglass.weebly.com/ Photos of replacing glass elements] *[http://www.glassian.org/Prism/Het_Bouwbedrijf/making_vault_lights.html Photos of making concrete-frame vault lights] *[http://castironpavementlights.com/replacement-of-traditional-pavement-lights/ Making cast-iron-frame pavement lights (including replicas)]
Category:Solar architecture Category:Energy-saving lighting Category:Glass architecture Category:Prisms (optics) Category:Sidewalks