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Fraunhofer Institute
for Building Physics
Fraunhofer Institute
for Solar Energy Systems

System database
Façade design


Data protection

Short description

API for light distribution curves from BTDF-data and sky luminances

The method of computation accessible through API allows to predict room lighting situations for various façade systems by using different daylighting calculation programs. Measured or calculated external luminance distributions will be calculated along with the actual photometric system descriptions to obtain luminous intensity distributions, which will then be used to predict the indoor lighting conditions. General features of this method include:


Consideration of arbitrary luminance distributions in the exterior space.


Consideration of arbitrary interior geometries by providing interfaces to existing daylight simulation programs.


Consideration of nearfield photometric relations between the façade element and the exterior space on the one hand and the interior points of observation on the other hand.


Control procedures for dynamic façade systems with different command variables (position of the sun, for instance).


Storage- and time-efficient interpolation methods for incicatrices of diffusion merely determined for discrete façade angles.

Schematic representation of the developed calculation method to determine room illumination through CFS façade sytems. Instead of calculating the daylight transmitted through a façade element using a simple model as one would for a standard glazing, the method converts the external luminace distribution as visible from the façade component into an indoor luminous intensity distribution taking into account the façade system's measured or computed BTDF. These lumious intensity distributions are imprinted upon the inward facing surfaces representing the CFS, which illuminate the space. By analogy with the modelling of luminares, the façade elements are therefore converted into light emitting surfaces.

The COM-based API is available to application designers. If you are envisaging such an integration, please contact us directly.

Dr.-Ing. Jan de Boer, Fraunhofer Institute for Building Physics,
E-mail: jdb@ibp.fhg.de