Measurements of Reflection and Transmission Behavior

These measurements are used in a variety of applications:

• Architecture and construction: Evaluating the light transmittance and reflectance of window glass and façade materials, for example, to optimize energy efficiency, building functionality and visual comfort, through material selection.
• Photovoltaics: Optimizing the efficiency of solar cells and evaluating photovoltaic modules regarding their glare potential.
• Automotive industry: Analysis of light reflectance and transmittance of paints and coatings to improve vehicle aesthetics and safety.
• Computer graphics: Creation of realistic renderings by accurately simulating the interaction of light with various surfaces and materials.
• Materials science: Characterization of new materials to evaluate their optical properties, e.g. during product development and improvement.

At Fraunhofer ISE, we perform high-resolution measurements of the spatial distribution of light from materials used in building envelopes. In the construction industry, particularly concerning building envelopes, such measurements of the reflection and transmission properties of building materials are of particular relevance. This is because products are designed here that must meet both aesthetic and functional requirements. 

With our 3D scanning goniophotometer PGII (“PGII” from pab advanced technologies Ltd.), we at Fraunhofer ISE offer a versatile measuring instrument for the optical characterization of solid materials and small lamps.

The measurements we perform enable architects and planners to select materials specifically for their projects in order to optimize the comfort and functionality of buildings. At the same time, manufacturers benefit from our customized support in developing and improving their products. In addition, our measurements can serve as a basis for valuable analysis and simulation options, for example, to analyze how humans perceive brightness under different lighting conditions. Such analyses improve the understanding of light interactions, allow the overall appearance of materials to be optimized and help to avoid glare.

The goniophotometer can be used to determine the bidirectional scattering distribution function (BSDF) of a material sample. The BSDF includes both the bidirectional transmittance distribution function (BTDF) of the light passing through the sample and the bidirectional reflectance distribution function (BRDF) of the light reflected by the sample.

During a measurement, a robotic arm rotates around the illuminated sample and captures light with high spatial resolution. The data sets contain hundreds of thousands of measurement values for different positions on the virtual sphere surface defined by the detector’s path (expressed in spherical coordinates). The measurements can be performed for different angles of incidence of the light and different angles of rotation of the material sample (in the case of anisotropic samples), as well as for different spectra of the light source. The data sets can then be converted into XML files in the Klems or tensor tree data formats, which allows us to use the results in computer graphics, simulations and visualizations.