Window sizing procedures based on vertical illuminance and degree of discomfort glare in buildings interiors

This study outlines a simplified mathematical approach to determine window dimensions for a given room based on two lighting quality indicators, namely, discomfort glare and vertical illuminance. The former represents visual comfort and is expressed in terms of daylight glare index (DGI). The latter reflects on the aspect of receiving sufficient light exposure to maintain optimal health and psychological wellbeing. It is represented by vertical illuminance at the eye level. The result offers a formula that puts forward a simple relationship between the window width, the window height and a specific (desired) depth of a given point in the space. A generic design scenario is used to illustrate the current method. The examined daylighting design criteria are of DGI=20 and E_v= 2500 lux. In conclusion, this paper proposes the glare criterion as additional to existing national window sizing procedures based on critical illuminance levels (or minimum daylight factor on the working plane corresponding to the critical visual tasks) and critical exterior conditions (that occur with absence of sunlight and a CIE Overcast Sky standard).