User assessment of fabric shading devices with a low openness factor

Abstract

Providing adequate glare protection and a view to the outside through fabric shading devices is challenging because these two objectives require conflicting material properties for a fully lowered shading. In a semi-controlled office-like experiment involving 32 participants, we investigated four types of neutrally-colored fabrics (charcoal and gray) with Openness Factors (OF) smaller than 7% focussing on view clarity, discomfort glare with the sun in the field of view, and participants' behavior when it comes to blind control. The results show that fabrics with OF<3% could provide adequate glare protection but no satisfactory view out. The charcoal-colored fabric with OF>6% resulted in lower glare protection but higher quality of view out. Our results show inconsistencies with the EN14501 blind classifications for glare and visual contact (i.e., view clarity), but acceptable agreement with the view clarity index, especially for the fabrics with the highest light transmittance. During the final session, three quarters of participants raised the blinds to allow an average of 10° view to the outside, reporting as primary motivations the wish for more light and view out. Despite the relatively small rise of the fabric (15% of the total shade), daylight levels and view out were significantly improved, suggesting that operable blinds should not be controlled nor described according to the "all-or-nothing" approach. The change in fabric height did not compromise glare perception. These results suggest that if the control of shading height is effectively provided to occupants, then the fabric material could be selected primarily based on glare requirements.