Abstract: A louver assembly for semi-circular, non-perfect or imperfect arch frame assemblies with louvers rotably mounted therein. A tensioning mechanism keeps the louvers taut between an arched frame member and a smaller anchorage frame member. An actuating mechanism is used to rotate the louvers upon the application of a predetermined force to a chain that coacts with teethed sprockets coupled with hooked clip members that removably hold the louvers. In this manner, the louvers are rotated between two extreme positions.