Anidolic lighting systems use anidolic optical components to light rooms. Light redirected by these systems does not converge to a focal point or form an image, whence the name (from an, without, and eidolon, image).
Anidolic lighting uses non-imaging mirrors, lenses, and light guides to capture exterior sunlight and direct it deeply into rooms, while also scattering rays to avoid glare. The human eye's response to light is non-linear, so a more even distribution of the same amount of light makes a room appear brighter.
Lens systems use reflection and refraction within optical prisms to redirect daylight. Some forms of prims lighting have been used for centuries, and others are 21st-century.
Deck prisms were set into the upper decks of ships to light the decks below. Pavement lights were set into floors or sidewalks to let light into a basement below. The underside was frequently extended into prisms to direct and spread the light.
Prism tiles were designed to bend sunbeams coming through a window upwards, so that they would reach deeper into a room. They were placed in the upper parts of window frames, where they were called "transom lights".
Anidolic mirror lighting systems can be divided into three parts:
- daylight capture, usually with zenithal light collector
- optimal transmission of the light (via anidolic ceilings, light tubes, etc.)
- distribution of captured light to target areas inside the rooms
Typically, light is captured with a compound parabolic collector (CPC) or elliptical collector (CEC) mounted on the exterior wall. These mirrors provide a wide and even collection pattern. The vertical capture angle approaches 90 degrees, from the horizon to the vertical plane of the supporting wall. An even capture pattern alleviates the need for a solar tracker: a permanently fixed anidolic collector remains effective at any time of day.
Snow and weatherproofing are also a consideration.
Unlike the industrial parabolic troughs used in solar concentrators, architectural CPC mirrors do not concentrate captured light into a single focal point or focal line (which creates a fire hazard). Instead, light is directed into the building through a relatively wide opening.
A second CPC or CEC mirror acting as an angle transformer disperses this beam into a wide-angle, diffused pattern. If it transmits light from a wide external CPC, a light tube actually becomes a flat anidolic ceiling.
Integrated anidolic systems reduce external protrusion and attempt to visually blend into traditional facades. However, like other anidolic systems, they are susceptible to glare and offer no protection from overheating on sunny days.
For example, the external CPC in the reference lights a 6-metre deep room. It protrudes 0.67 metres from the exterior wall and employs a 3.6 metre long, 0.5 meter tall light tube, followed by a 0.9 metre long interior CPC, to deliver captured light into the back of the room. This arrangement provided 32% energy savings over a six-month period compared to a reference facade.
- Chaves, p. 72
- Scartezzini, p. 14
- Macky, Ian, "Prism glass", Glassian
- Padiyath, Raghunath; 3M company, St Paul, Minnesota (2013), Daylight Redirecting Window Films, U.S.A. Department of Defense ESTCP Project number EW-201014, retrieved 2017-10-09CS1 maint: multiple names: authors list (link)
- Chaves, p. 146
- See Chaves, pp.75, for a discussion on angle transformer properties.
- Scartezzini, p. 15
- Chaves, Julio (2015). Introduction to Nonimaging Optics, Second Edition. CRC Press. ISBN 978-1482206739.
- J.-L. Scartezzini (2003). "Advances in daylighting and artificial lighting". Research in Building Physics: Proceedings of the 2nd International Conference on Building Physics, 14–18 September 2003, Antwerpen, Belgium. Taylor & Francis. ISBN 978-90-5809-565-7.