vertically toward the floor each louver generally extends below the horizontal plane of the top of the adjacent louver that is located nearer to the center axis 16 see for example fig3 where the bottom of louver 21 partially obscures the top of louver 22 each quadrant is independent of all others so a louver assembly 9 may be used in any combination of the quadrants see fig3 10 for illustrations of various combinations the preferred embodiment uses removable louver assemblies that can be positioned on the outside of any one or more or all quadrants of the lens frame 8 as disclosed above the preferred embodiment comprises a lens 7 that is substantially in the shape of a half globe with louvers mounted on the outside of the lens 7 on a lens frame 8 however the lens 7 and the louvers 9 could be altered and still remain within the scope of this invention the lens 7 could be of cylindrical frustoconical or rectangular shape to name a few shapes the lens 7 could be constructed of different materials furthermore both the location and the method of attachment of the louvers 9 could be varied for example the louvers 9 could be attached directly to the housing 2 the lens 7 or the ceiling also the louvers 9 could be attached to the inside or outside of the lens when the louvers are not present the light rays.