Goniophotometric and Photometric Characterization of Bulk-diffusing Glazings

Augusto Maccari,Marco Montecchi, Enrico Nichelatti, Michele Zinzi

Transparent glazings are used in architecture when there is a need for a perfect view through. If this is not necessary, diffusing glazings can be used to prevent glare effects and to distribute in a more uniform way the daylight in interiors.
Several kinds of diffusing glazings are commercially available for building applications. The authors have already performed daylighting characterisations of some commercial diffusing products: sand-blasted glasses, laminated glass panes with diffusing plastic sheets and hollow glass blocks.
Goniophotometric and photometric measurements were performed on these kinds of samples. An extrapolation procedure based on the use of integrating sphere entrance ports with different diameters was applied in order to perform accurate evaluations of the light transmittance of the glazings. The dependence of the measured transmittance as a function of the port diameter presented an increasing exponential-like behaviour.
For finding the asymptotic value (corresponding to a sufficiently large diameter), which can be considered as the effective light transmittance of the sample, an analytical model was carried out.
The same measurement procedures are applied in this paper on thick bulk-diffusing glazings: two marble-glass panes of different thicknesses consisting in marble sheets coupled to glass sheets of the same thickness.
For simplicity reasons, only normal incidence transmittance measurements were performed. More precisely, normal hemispherical transmittance values were measured with small and large integrating spheres, while the goniophotometric measurements supplied normal directional transmittance values.

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