An accurate evaluation of daylight distribution through advanced fenestration systems (complex glazing, solar shading systems) requires the knowledge of their Bidirectional light Transmission (Reflection) Distribution Function BT(R)DF. An innovative equipment for the experimental assessment of these bi-directional functions has been developed, based on a digital imaging detection system. An extensive set of BTDF measurements was performed with this goniophotometer on Venetian blinds presenting curved slats with a mirror coating on the upper side. In this paper, the measured data are compared with ray-tracing results achieved with a virtual copy of the device, that was constructed with a commercial ray-tracing software. The model of the blind was created by implementing the measured reflection properties of the slats coatings in the ray-tracing calculations. These comparisons represent an original and objective validation methodology for detailed bi-directional properties for a complex system; the good agreement between the two methods, yet presenting very different parameters and assessment methodologies, places reliance both on the digital-imaging detection system and calibration, and on the potentiality of a flexible calculation method combining ray-tracing simulations with simple components measurements.

1 aAndersen, Marilyn1 aRubin, Michael, D.1 aPowles, Rebecca1 aScartezzini, Jean-Louis uhttps://buildings.lbl.gov/publications/bi-directional-transmission00435nas a2200133 4500008004100000050001500041245002600056210002400082260006700106100002200173700002000195700002300215856006300238 2002 eng d aLBNL-5214800aOptics Version 5.1.010 aOptics Version 5101 aBerkeley, CAbRegents of the University of Californiac11/20021 aVersluis, Richard1 aPowles, Rebecca1 aRubin, Michael, D. uhttps://buildings.lbl.gov/publications/optics-version-510101305nas a2200145 4500008004100000050001500041245005600056210005600112260003000168520082500198100002001023700002401043700002201067856007001089 2002 eng d aLBNL-4955500aSolar Absorption in Thick and Multilayered Glazings0 aSolar Absorption in Thick and Multilayered Glazings aCologne, Germanyc07/20023 aThick and multilayered glazings generally have a nonuniform distribution of absorbed solar radiation which is not taken into account by current methods for calculating the center of glass solar gain and thermal performance of glazing systems. This paper presents a more accurate method for calculating the distribution of absorbed solar radiation inside thick and multilayered glazings and demonstrates that this can result in a small but significant difference in steady-state temperature profile and Solar Heat Gain Coefficient for some types of glazing systems when compared to the results of current methods. This indicates that a more detailed approach to calculating the distribution of absorbed solar radiation inside glazings and resulting thermal performance may be justified for certain applications.

1 aPowles, Rebecca1 aCurcija, Dragan, C.1 aKohler, Christian uhttps://buildings.lbl.gov/publications/solar-absorption-thick-and01360nas a2200145 4500008004100000050001500041245006400056210006400120260002700184300001000211520087000221100002301091700002001114856008001134 2000 eng d aLBNL-4832200aOptical Properties of Glazing Materials at Normal Incidence0 aOptical Properties of Glazing Materials at Normal Incidence aParis, Francec10/2000 a13-163 aMeasurements of spectral transmittance T and reflectance R at normal incidence continue to be the most common and accurate source of energy performance data for glazing materials. Prediction of these radiometric properties from more fundamental materials data is often confounded by the complexity and uncertainty of coating structures. Angle-dependent radiometric properties of coated glazing will probably be predicted from normal-incidence data rather than being measured at many angles. The general error level demonstrated in round-robin tests is on the order 1-2%; it is often necessary to achieve better levels of performance. Based on results obtained following the round-robin tests, it is expected that accuracy of better than 0.5% can be generally achieved. A new type of absolute standard reference is described and tested with promising results.

1 aRubin, Michael, D.1 aPowles, Rebecca uhttps://buildings.lbl.gov/publications/optical-properties-glazing-materials01963nas a2200157 4500008004100000050001500041245008200056210006900138300001200207490000700219520143900226100002301665700002001688700002301708856007401731 1998 eng d aLBNL-4070500aModels for the Angle-Dependent Optical Properties of Coated Glazing Materials0 aModels for the AngleDependent Optical Properties of Coated Glazi a267-2760 v663 aOptical transmittance and reflectance of window materials can be measured accurately at normal incidence using standard equipment. Sunlight often strikes at angles for which the transmittance and reflectance are significantly different from their values at normal incidence. A reliable procedure for extrapolating from normal properties to oblique properties is thus needed for accurate annual energy performance calculations and product comparisons. The structural models for the materials are greatly constrained by the limited amount of data that is usually available. For monolithic materials such as uncoated glass or plastic substrates it is possible to solve directly for the optical indices and then apply Fresnels equation to obtain the oblique properties. For coated glass, the situation is more complex, but a numerical solution is often possible. First, detailed optical models were constructed and accurate angle-dependent data were generated for a wide selection of coated glazing materials. Then, a set of very simple thin-film models were chosen that would converge given a limited amount of data. At 60 degree incidence, the monolithic model was often accurate to within 2% but frequently deviated farther up to 8%. The single-layer thin-film model fared little better. Highly constrained multilayer models often deviated less than 1% although convergence became increasingly specific to similar coating types.

1 aRubin, Michael, D.1 aPowles, Rebecca1 avon Rottkay, Klaus uhttps://buildings.lbl.gov/publications/models-angle-dependent-optical01554nas a2200157 4500008004100000050001500041245001800056210001800074300001200092490000700104520116200111100002301273700002301296700002001319856005701339 1997 eng d aLBNL-3991100aWindow Optics0 aWindow Optics a149-1610 v623 aOptical and radiative properties of glazing materials are primary inputs for determination of energy performance in buildings. This paper revisits the problem and reformulates the calculations to encompass a variety of solutions to practical problems in window optics. Properties of composite systems such as flexible films applied to rigid glazing and laminated glazing can be predicted from measurements on isolated components in air or other gases. Properties of a series of structures can be generated from those of a base structure. For example, the measured properties of a coated or uncoated substrate can be extended to a range of available substrate thicknesses without the need to measure each thickness. Similarly, a coating type could be transferred by calculation to any other substrate. A simple monolithic model for extrapolating from normal properties to oblique properties is shown to have sufficient accuracy for the purpose of annual energy performance calculations. A process is initiated to develop a reliable method for determination of effective indices suitable for more detailed spectral and directional optical calculations.

1 aRubin, Michael, D.1 avon Rottkay, Klaus1 aPowles, Rebecca uhttps://buildings.lbl.gov/publications/window-optics