Original: Louvers originated in the Middle Ages as lantern-like constructions in wood that were fitted on top of roof holes in large kitchens to allow ventilation while keeping out rain and snow .
Simplified: Dariusz Heim and Kamil Kieszkowski : Shading , PLEA2006 - The 23rd Conference on Passive and Low Energy Architecture , Geneva , Switzerland , 6-8 September 2006