Converging through the window

Winter usually invites everybody to sit down in a comfortable armchair and enjoy the heat coming from a stove or the sunlight passing through the window. The glass of windows is commonly smooth, and the light passes through it without appearing to deviate from its path.¹ It is refracted going into the glass but is refracted again as it leaves, so that it leaves the glass in the same direction as it arrived. However, in some cases, windows of street-level homes have translucent glass that allows the light to pass through but does not provide a clear view of the other side of the glass. This glass makes each sunray leave the surface at a random direction, similar to Fig. 2 of Ref. 2. Another possibility is using glass with a certain periodic shape such as a 2D lens array³ [Fig. 1(a)]. If we look closer,...