Based on the simple case with one window, an obstruction opposite to the window is con­sidered here, as represented in Figure 6. It is assumed that the obstruction shows horizon­tal symmetry with respect to the window centre. Then three additional factors apply: the horizontal and vertical obstruction angles a and ф, respectively, and the average obstruc­tion reflectivity p. These factors replace pW, pD and d of the original case. The floor reflec­tion is now much more important than the reflections of walls and ceiling because due to the obstruction zenith light is the main daylight source. The results are shown in Figure 7.

The daylight quantity is reduced by appr. 30% as compared to the un-obstructed case. The vertical obstruction size and the lintel height show strong negative effects. The single factor effects show a greater uniformity.

Figure 7: Factors, definition bounds and resulting main effects on D for the case of the room daylit by one window with an obstruction opposite