Prism lighting is the use of

prism Prism usually refers to: * Prism (optics), a transparent optical component with flat surfaces that refract light * Prism (geometry), a kind of polyhedron Prism may also refer to: Science and mathematics * Prism (geology), a type of sedimentary ...

s to improve the distribution of light in a space. It is usually used to distribute daylight, and is a form of anidolic lighting. Prism lighting was popular from its introduction in the 1890s through to the 1930s, when cheap electric lights were commonplace and prism lighting became unfashionable. While mass production of prism lighting systems ended around 1940, the 2010s have seen a revival using new materials.

How it works

The human eye's response to light is non-linear: halving the light level does not halve the perceived brightness of a space, it makes it look only slightly dimmer. If light is redistributed from the brightest parts of a room to the dimmest, the room therefore appears brighter overall, and more space can be given a useful and comfortable level of illumination (see before and after images from an 1899 article, below). This can reduce the need for artificial lighting.

Refraction In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenome ...

and

total internal reflection Total internal reflection (TIR) is the optical phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflect ...

inside optical prisms can bend beams of light. This bending of the light allows it to be redistributed. Many small prisms may be joined at the edges into a sheet. A prism sheet is somewhat like a linear

Fresnel lens A Fresnel lens ( ; ; or ) is a type of composite compact lens developed by the French physicist Augustin-Jean Fresnel (1788–1827) for use in lighthouses. It has been called "the invention that saved a million ships." The design allows the c ...

, but each ridge may be identical. Unlike a Fresnel lens, the light is not intended to be focussed, but used for anidolic lighting. Image:Before prism lighting.jpg, alt=Woodcut? of a deep, shadowy room with light only near the window at the far end, Uneven light from a window. Image:After prism lighting.jpg, alt=Woodcut? of the same room, but much more evenly lit, with diffuse light in the former shadows, The same light, redistributed by prism tiles in the window. Image:Scatter.gif, alt=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., Single pendant prism from a vault light, showing

Image:2angles.gif, alt=Two vertical tiles with one side of each serrated into prisms (the two sheets of prisms are differently shaped), Two different prescriptions of prism tiles, showing their differing

refraction In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenome ...

of the light. The angle of the incoming light differs, but the outgoing angle of the outgoing light is the same (optimally, nearly horizontal).

Types

Deck prisms carried light through the upper decks of ships and spread it in the decks below. Similarly, on land, prisms in sidewalk lights were used to light basements and vaults. Prism tiles were used vertically, usually as a transom light above a window or door. They were also built into fixed and movable canopies, sloped glazing, and

skylights A skylight (sometimes called a rooflight) is a light-permitting structure or window, usually made of transparent or translucent glass, that forms all or part of the roof space of a building for daylighting and ventilation purposes. History Open ...

. They bend light upwards, so that it penetrates more deeply into the room, rather than lighting the floor near the window. Modern prismatic panels are essentially an acrylic version of the old glass prism tiles. Like glass tiles, they can be mounted on adjustable canopies.https://fenix.tecnico.ulisboa.pt/downloadFile/395139483932/Resumo-alargado-aluno-53255.pdf Channel panels use slits that reflect light internally.

Holographic optical element Holographic optical element (HOE) is an optical component (mirror, lens, directional diffuser, etc.) that produces holographic images using principles of diffraction. HOE is most commonly used in transparent displays, 3D imaging, and certain scannin ...

s can also be used to redirect light.

Daylight redirecting window film Daylight redirecting film (DRF) is a thin, flexible plastic film which can be applied to a window to refract or reflect incoming light upwards, so that the deeper parts of the room are lit more evenly. It can be used as a substitute for opaque bl ...

(DRF) is a thin, flexible peel-and-stick sheet, with the optical layer generally made of acrylic. There are two types of film. Some film is moulded with tiny prisms, making a flexible peel-and-stick miniature prismatic panel. Other film is moulded with thin near-horizontal voids protruding into or through the acrylic; the slits reflect light hitting their top surfaces upwards.https://sweets.construction.com/swts_content_files/154130/2263001.pdf Refraction is minimized, to avoid colouring the light. The reflection-based films are more transparent (both are translucent), but they tend to send the light up at the ceiling, not deeper into the room. Refraction-based films are translucent rather than transparent, but offer finer control over the direction of the outgoing light beam; the film can be made in a variety of prism shapes to refract light by a variety of angles.

Manufacture and repair

Older glass elements were cast, and might be cut and polished. Prism tiles were often made of single prisms joined with zinc, lead, or electroglazed copper strips (rather like the methods used to join traditional European stained glass). Sidewalk prisms were cast in one piece as single or multiple-prism lenses, and inserted into load-bearing frames. Daylight redirecting film is made of

acrylic Acrylic may refer to: Chemicals and materials * Acrylic acid, the simplest acrylic compound * Acrylate polymer, a group of polymers (plastics) noted for transparency and elasticity * Acrylic resin, a group of related thermoplastic or thermosett ...

.Daylight Redirecting Window Film
Energy Efficiency Emerging Technologies. Damaged prism tiles may be repaired, and as they came in standard designs, there is a salvage market in replacements. Replacements for one-piece castings can be commissioned. Weakened prism tiles may be reinforced with hidden bars, much like those used to reinforce stained glass.

Architectural design

Sophisticated systems for lighting different sorts of spaces with prism tiles were developed. Generally, the goal was to send the available light across the room nearly horizontally. One company sold tiles with nine prescriptions, giving different angles of refraction. Different prescriptions were often used in different parts of the same window transom, sometimes to disperse the light vertically, and sometimes to bend light horizontally around obstacles like pillars. Prisms tiles sometimes has elaborate artistic designs moulded into the outside;

Frank Lloyd Wright Frank Lloyd Wright (June 8, 1867 – April 9, 1959) was an American architect, designer, writer, and educator. He designed more than 1,000 structures over a creative period of 70 years. Wright played a key role in the architectural movements o ...

created over forty prism tile designs.Renovation of Sheldon Munn uncovers exciting find
Ames Tribune, Wednesday Sep 28, 2016 at 10:59 AM and 10:17 PM, by Michael Crumb Prism lighting works more effectively in light, open spaces. Some believe that it contributed to the trend away from dark, subdivided Victorian interiors to open-plan, light-coloured ones. The removal or covering of old prism transom lights often leaves characteristically tall signage spaces over shop windows (see pictures).

was initially made of one redirecting film and one glare-reducing diffusing film, often located on different interior surfaces of a double-glazed window, but integrated single films are now available. Some daylight redirecting films reflect incoming light upwards off tiny near-horizontal reflectors, so at high sun angles they bend it sharply, throwing it upwards to the ceiling, where a typical ceiling diffuses the daylight somewhat deeper into the space. Other daylight redirecting films refract light at any specified angle, ideally sending it nearly horizontally into the room. Redirecting films can be used as a substitute for opaque blinds.

Gallery

File:Awning with show window.gif, Daylighting a shop with a display window using prism tile transoms File:Rebuilt glass panels.jpg, An outside view of such a store ( broader view, closer view) File:Hamm building closeup.jpg, The same store before the prism lights were restored, showing characteristic proportioning File:Shelden-Dee_Block_Houghton_MI.jpg, A building with original transom prisms for the shops File:Lucidux daylighting.gif, Two-stage refraction for basement lighting File:Prism salesroom.gif, The system in use to light a salesroom inside a hollow sidewalk. The ceiling and the wall on the right are prisms. File:Basement diagram stall light.gif, Diagram of a stall-board prism light. This system can also daylight a basement without a hollow sidewalk. File:Canopies in court.gif, Prism glass canopies in a courtyard, to bend near-vertical light sideways into the windows File:Straight lightwell.gif, A scheme for a light well, with progressively larger prism canopies lower down File:Tapering lightwell.gif, Tapered space-saving light well designed for use with prism lighting

References

{{reflist , refs=f Object of the Moment: 3M Daylight Redirecting Film by 3M
by Selin Ashaboglu, March 02, 2017 {{Citation , last = Macky , first = Ian , title = Prism glass , website = Glassian , url =http://www.glassian.org/Prism/ {{Citation , last = Macky , first = Ian , title = Luxfer Products , website = Glassian , url =https://glassian.org/Prism/Luxfer/products.html {{Citation, author2 = 3M company, St Paul, Minnesota, last = Padiyath, first = Raghunath, title = Daylight Redirecting Window Films, access-date = 2017-10-09, date = 2013, series = U.S.A. Department of Defense ESTCP Project number EW-201014 , url = https://www.serdp-estcp.org/Program-Areas/Energy-and-Water/Energy/Conservation-and-Efficiency/EW-201014 {{cite book , first1=Chad , last1=Randl , year=2001 , title=Repair and Reproduction of Prismatic Glass Transoms , url=https://www.nps.gov/tps/how-to-preserve/tech-notes/Tech-Notes-Glass01.pdf , publisher=National Park Service , oclc=62544368 {{Citation , editor1= 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 Solar architecture Energy-saving lighting Glass architecture Prisms (optics)

How it works

Types

Manufacture and repair

Architectural design

Gallery

See also

References