Anidolic lighting
Encyclopedia
Anidolic lighting systems use anidolic or nonimaging optical
components (typically parabolic
or elliptical
mirrors) to capture exterior sunlight
and direct it deeply into rooms, while also scattering rays to avoid glare. Anidolic, or non-imaging, mirrors are traditionally used in industrial solar concentrators. Light captured and narrrowed by these mirrors in daylighting
applications does not converge into a single focal point
; the system is unable to form an image of the light source and is thus called non-imaging, or anidolic (from Greek an: without, eidolon:image). The same concept has been tested for interior lighting applications; they attempt at solving the most challenging objective – effective capture and redistribution of light on cloudy, overcast days.
Design of anidolic lighting systems breaks down to three critical parts:
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, with vertical capture angle approaching 90 degrees, from the horizon
to the vertical plane of the supporting wall. Unlike industrial parabolic trough
s, architectural CPC does 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. Even capture pattern, correlating with low concentration ratio, alleviates the need for a solar tracker
: a permanently fixed anidolic collector remains effective at any time of day. A second CPC or CEC acting as angle transformer disperses this beam into a wide-angle, diffused pattern.
Reference external CPC for a 6 meter deep room protrudes 0.67 meter from the exterior wall and employs a 3.6 meter long, 0.5 meter tall light tube
, followed with a 0.9 meter long interior CPC, to deliver captured light into the back of the room (with wide external CPC, light tube actually becomes a flat anidolic ceiling). This arrangement provided 32% energy savings over a six month period compared to a reference facade.
External parabolic collectors require proper heat insulation, double-glazed windows over the zenithal opening and roller blinds to reduce excessive lighting, glare and heat on sunny days. Integrated anidolic systems reduce external protrusion and attempt to visually blend into traditional facades, however, like all anidolic systems, they are susceptible to glare and offer no protection from overheating on sunny days.
Nonimaging optics
Nonimaging optics is the branch of optics concerned with the optimal transfer of light radiation between a source and a target...
components (typically parabolic
Parabolic reflector
A parabolic reflector is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis...
or elliptical
Ellipse
In geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis...
mirrors) to capture exterior sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...
and direct it deeply into rooms, while also scattering rays to avoid glare. Anidolic, or non-imaging, mirrors are traditionally used in industrial solar concentrators. Light captured and narrrowed by these mirrors in daylighting
Daylighting
Daylighting is the practice of placing windows or other openings and reflective surfaces so that during the day natural light provides effective internal lighting. Particular attention is given to daylighting while designing a building when the aim is to maximize visual comfort or to reduce energy...
applications does not converge into a single focal point
Focus (optics)
In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by...
; the system is unable to form an image of the light source and is thus called non-imaging, or anidolic (from Greek an: without, eidolon:image). The same concept has been tested for interior lighting applications; they attempt at solving the most challenging objective – effective capture and redistribution of light on cloudy, overcast days.
Design of anidolic lighting systems breaks down to three critical parts:
- zenithZenithThe zenith is an imaginary point directly "above" a particular location, on the imaginary celestial sphere. "Above" means in the vertical direction opposite to the apparent gravitational force at that location. The opposite direction, i.e...
al light collector for capturing daylight; - optimal collection and distribution of captured light to target areas (anidolic ceilings, light tubeLight tubeLight tubes or light pipes are used for transporting or distributing natural or artificial light. In their application to daylighting, they are also often called sun pipes, sun scopes, solar light pipes, sky lights or daylight pipes.Generally speaking, a light pipe or light tube may refer to:* a...
s etc.); - optimal integration into the building facadeFacadeA facade or façade is generally one exterior side of a building, usually, but not always, the front. The word comes from the French language, literally meaning "frontage" or "face"....
.
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, with vertical capture angle approaching 90 degrees, from the horizon
Horizon
The horizon is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting...
to the vertical plane of the supporting wall. Unlike industrial parabolic trough
Parabolic trough
A parabolic trough is a type of solar thermal energy collector. It is constructed as a long parabolic mirror with a Dewar tube running its length at the focal point. Sunlight is reflected by the mirror and concentrated on the Dewar tube...
s, architectural CPC does not concentrate captured light into a single focal point
Focus (optics)
In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by...
or focal line (which creates a fire hazard); instead, light is directed into the building through a relatively wide opening. Even capture pattern, correlating with low concentration ratio, alleviates the need for a solar tracker
Solar tracker
A solar tracker is a generic term used to describe devices that orient various payloads toward the sun. Payloads can be photovoltaic panels, reflectors, lenses or other optical devices....
: a permanently fixed anidolic collector remains effective at any time of day. A second CPC or CEC acting as angle transformer disperses this beam into a wide-angle, diffused pattern.
Reference external CPC for a 6 meter deep room protrudes 0.67 meter from the exterior wall and employs a 3.6 meter long, 0.5 meter tall light tube
Light tube
Light tubes or light pipes are used for transporting or distributing natural or artificial light. In their application to daylighting, they are also often called sun pipes, sun scopes, solar light pipes, sky lights or daylight pipes.Generally speaking, a light pipe or light tube may refer to:* a...
, followed with a 0.9 meter long interior CPC, to deliver captured light into the back of the room (with wide external CPC, light tube actually becomes a flat anidolic ceiling). This arrangement provided 32% energy savings over a six month period compared to a reference facade.
External parabolic collectors require proper heat insulation, double-glazed windows over the zenithal opening and roller blinds to reduce excessive lighting, glare and heat on sunny days. Integrated anidolic systems reduce external protrusion and attempt to visually blend into traditional facades, however, like all anidolic systems, they are susceptible to glare and offer no protection from overheating on sunny days.
See also
- Architectural light shelfArchitectural light shelfA light shelf is an architectural element that allows daylight to penetrate deep into a building. This horizontal light-reflecting overhang is placed above eye-level and has a high-reflectance upper surface...
- Light tubeLight tubeLight tubes or light pipes are used for transporting or distributing natural or artificial light. In their application to daylighting, they are also often called sun pipes, sun scopes, solar light pipes, sky lights or daylight pipes.Generally speaking, a light pipe or light tube may refer to:* a...
- Passive solar building designPassive solar building designIn passive solar building design, windows, walls, and floors are made to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer...
- Sunroom