Prism lighting is the use of prisms 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 commonplace lighting 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
If light is redistributed from the brightest parts of a room to the dimmest, more space can be given a useful and comfortable level of illumination (see before and after images from a 1899 article, below). This can reduce the need for artificial lighting.
Refraction and total internal reflection 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 , but each ridge may be identical. Unlike a Fresnel lens, the light is not intended to be focussed, but used for anidolic lighting .
Deck prisms with the decks below and below. Similarly, on land, prisms in sidewalk lights have been 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 movable canopies, sloped glazing, and skylights . They bend light upwards, so 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.  Channel panels use slits that reflects light internally. Holographic optical elements can also be used to redirect light.  
Daylight redirecting window film (DRF) is a thin, flexible peel-and-stick sheet, with the optical layer generally made of acrylic. Film is molded with thin near-horizontal voids protruding into or through the acrylic; the slits reflect light hitting their top surfaces upwards.   Refraction is minimized, to avoid coloring the light.  These reflection-based elements are more transparent (both are translucent) .
Manufacture and repair
Older glass elements were cast, and might be cut and polished. Prism tiles were often made of zinc, lead, or electroglazed copper strips (rather like the methods used to join traditional European stained glass ).  Sidewalk prismswere cast in one piece, single or multiple-prism lenses, and inserted into load-bearing frames. Daylight redirecting film is made of acrylic . 
Damaged prism tiles can be repaired, and 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. 
Sophisticated systems for lighting different types of spaces with prism tiles were developed. Generally, the goal is to send the light horizontally.  giving different angles of refraction .   Different prescriptions have often been used in the past, sometimes to disperse the light vertically, and sometimes to bend light horizontally around obstacles like pillars. 
Prisms tiles sometimes has elaborate artistic designs molded into the outside; Frank Lloyd Wright famously created over forty prism tile designs. 
Prism lighting works more effectively in light, open spaces.  Some believe that it contributes to the trend away from dark, subdivided Victorian interiors to open-plan, light-colored ones. [ citation needed ] The removal or covering of old prism transom lights often leaves characteristically tall signage spaces over shop windows (see pictures).
Daylight redirecting window film Was INITIALLY made of redirecting one movie and one glare-reducing diffusing film Often Located on different interior surfaces of a double glazed window,  purpose integrated single movies are now available.  Daylight redirect 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.  Redirecting movies can be used as a substitute for opaque blinds. 
- Anidolic lighting
- Vault lights
- Daylight redirecting film
- Restored Philadelphia shopfront
- ^ Jump up to:a b c Randl, Chad (2001). Repair and Reproduction of Prismatic Glass Transoms (PDF) . National Park Service. OCLC 62544368 .
- ^ Jump up to:a b c d e Padiyath, Raghunath; 3M company, St Paul, Minnesota (2013), Daylight Redirecting Window Films , US Department of Defense ESTCP Project number EW-201014 , retrieved 2017-10-09
- ^ Jump up to:a b c d e f Henry Crew, Ph.D., and Olin H. Basquin, AM, eds. (1898), “Pocket Hand-book of Electro-Glazed Luxfer Prisms Comprising Useful Information and Tables of Concern for Architects, Engineers and Builders.” , Glassian
- Jump up^ Ian Macky, “Prism Glass” , Glassian
- ^ Jump up to:a bhttps://fenix.tecnico.ulisboa.pt/downloadFile/395139483932/Resumo-alargado-aluno-53255.pdf [ full citation needed ]
- Jump up^ James, PAB; Bahaj, AS (2005). “Holographic optical elements: Various principles for solar control of conservatories and sunrooms”. Solar Energy . 78 (3): 441-54. Bibcode : 2005SoEn … 78..441J . doi : 10.1016 / j.solener.2004.05.022 .
- ^ Jump up to:a bhttps://sweets.construction.com/swts_content_files/154130/2263001.pdf [ full quote needed ]
- Jump up^ Daylight Redirecting Window Film, Energy Efficiency Emerging Technologies.
- Jump up^ Macky, Ian, “Luxfer Products” , Glassian
- Jump up^ Renovation of Sheldon Munn uncovering uncoveredAmes Tribune, Wednesday Sep 28, 2016 at 10:59 AM and 10:17 PM, by Michael Crumb
- Jump up^ Object of the Moment: 3M Daylight Movie Redirection by 3M, by Selin Ashaboglu, March 02, 2017