Experimental assessment of bi-directional transmission distribution functions using digital imaging techniques

Many daylighting applications require a precise knowledge of the directiona l transmission features of advanced fenestration materials. These photometr ic properties are described by a bi-directional transmission distribution f unction (BTDF), whose experimental assessment requires an appropriate equip ment. A novel bi-directional photogoniometer, based on digital imaging techniques , has been designed and developed for that purpose. The main advantages of this device ale the significant reduction of the time required for data mea surement and its capability to assess an almost continuous BTDF function. T hese features can be achieved only through detailed and accurate calibratio n procedures of the bi-directional photoeoniometer, which are described in this paper, together with digital image and data processing. Several experi mental results, obtained for different fenestration materials, are used to illustrate the capabilities of this novel equipment (C) 2001 Elsevier Scien ce B.V. All rights reserved.