Since it was first developed, nonimaging optics has been successfully applied to the design of solar concentrators. These devices collect sunlight falling on an entry aperture and concentrate it on a smaller exit aperture where the receiver is placed (e.g. a heat exchanger on a photovoltaic cell) reaching concentration factors close to the thermodynamic limit. When the light ray paths are reversed by replacement of the receiver with a light emitting source, the same kind of device can be used as a highly efficient luminaire capable of delivering light through beams of well-defined angular spread.
In daylighting systems, light has to be collected, channelled through the building envelope and delivered into a room with maximum efficiency. Usually these systems (e.g. lightshelves, skylights) are located well above the occupants heads’ height and are not meant to provide a clear view of the outside environment.
Nonimaging optics deals with the optimal transfer of light without considering image distortions that may occur. Therefore, its theoretical framework appears very appropriate for the design of new daylighting systems.
To clearly mark the use of nonimaging optics principles for the design of such systems, we name them “anidolic daylighting systems” where “anidolic” is a synonym of “nonimaging”, constructed from two words of ancient Greek (“an”=without, “eidolon”=image). In French, this word sounds much better than the literal translation “Optique Sans Formation d’Image (OSFI)”.
Although many daylighting systems can claim to be inherently “nonimaging”, the qualifier “anidolic” applies only to those systems that have been designed using the concepts and tools found within the nonimaging optics theoretical framework (e.g. conservation of the “etendue” of light beams using the edge-ray principle).
Typical characteristics of anidolic systems are:
- sharp cut-off angles for admitting or delivering light;
- very few reflections of the light rays when passing through the system.