Glazing daylight transmittances: a field survey of windows in urban areas

The effect of urban air pollution on glazing daylight transmittance was inv estigated by measuring the percentage loss in glazing transmittance of a nu mber of windows throughout a large city in the UK. A total of 430 windows i n a range of building types and locations were used to create the database for this window survey. The: measurements were taken under overcast sky con ditions to minimise errors that could occur during periods of rapidly chang ing sky luminance. In addition, two adjacent photocells were used so that s imultaneous comparative measurements were taken. In general it was observed that the loss in transmittance for a vertical window did not usually excee d 10%. The factors that most significantly reduced glazing daylight transmi ttance were (i) the function/use of the building or the rooms within, (ii) the inclination of the window and (iii) the shading of the window by overha ngs. It is, therefore, suggested that future daylight design guidelines sho uld include these factors. (C) 2000 Elsevier Science Ltd. All rights reserv ed.