Small-scale field study of window films’ impact on daylight availability under clear sky conditions

Abstract

Daylight illuminance levels and their spatial distribution are important design elements to achieve indoor visual comfort conditions and sustainability in buildings during the operation stage. While a proper daylighting scheme increases the efficiency of the building, the excessive use of glazed surfaces can contribute to thermal and visual discomfort, hence increasing the cooling demand and use of artificial lighting. Solar control film (SCF) is a self-adhesive thin film that can be applied on glazing systems of existing buildings for retrofitting purposes to modify thermal and optical properties of the glass substrate. This paper analyses experimentally the impact of single glazing with different SCFs on the indoor illuminance levels and respective distribution on horizontal work plane by comparing the measured absolute values and the useful daylight illuminance metric. Field experiments using a small scale model with the glazing oriented to the south, in Lisbon, were performed for a 6 mm clear glass and four different SCFs applied on the external surface of the glass, under clear sky conditions during summer and winter solstice at 9h00, 12h00, and 15h00. The results show that all SCFs reduced the indoor illuminance, which demonstrate their potential for glazing refurbishment when indoor visual discomfort occurs in buildings.