Light distribution in air-supported pneumatic structures: Comparison of experimental and computer calculated daylight factors

Abstract

This study examines daylight distribution and illumination levels with daylight factors (DFs) inside an air-supported (pneumatic) structure (50.0 m long, 25.0 m wide and 11.0 m high). The DFs values were determined experimentally for 45 different points on the playground floor. Two sets (set1 and set2) of time dependent illuminance measurements were performed at overcast but variable (5400-2400 lx) sky conditions similar to the CIE overcast sky. Results revealed that the DFs values were in the range from 1.1% to 1.7% and were not evenly distributed across the interior, with the greatest values at the centre and the smallest at the edges of the playground floor. Composition of the membrane was studied with SEM micrographs and by measuring the Raman and Infrared spectra. Hemispherical (total) transmittance (TT(λ)) and reflectance (TR(λ)) spectra (300–2500 nm) of the membrane used were measured and averaged over the visible spectral region giving TTvis and TRvis and haze, the latter confirming that fabrics strongly scattered the incoming solar radiation. The surface of the fabrics was characterized by contact angle measurements which indicates that the fabrics were weakly hydrophobic and strongly soiled. Daylight factor values obtained from the DAYSIM computer simulations matched well the experimental ones allowing further studies of daylighting inside the translucent dome. It was found that various colour patterns substantially affected the DFs values. DAYSIM calculations also demonstrated the possible use of aerogel insulation blanket as composite fabrics for air-supported structures.