The purpose of this work is the definition of a representative sky for the Geneva Lake Region (south-west Switzerland). A representative sky is a theoretical blended sky based on the relative occurrence of a subset of the 15 standard general skies suggested in 2003 by the Commission Internationale de l’Eclairage (CIE) [1]. By employing Tregenza’s method [4] and the Swiss Norm 150 911 [5], a reduced set of CIE standard skies (and their relative frequency of occurrence), named the Geneva Lake Region Representative Sky (GLRRS), is proposed. In addition, by means of a GLRRS-based Virtual Sky Dome (VSD) and the lighting software Photopia 3.0, the behaviour of three different kinds of mirror lightducts is simulated for the Geneva Lake Region.