Abstract: A Venetian blind system for the interior of greenhouses having pitched overhead windows and arcuate windows merging into vertical side windows including a first Venetian blind having a head channel secured at the peak of the greenhouse and a bottom channel detachably secured at the lower end of the pitched windows, and slats supported by ladders suspended between the channels, the first blind being provided with springs within the bottom channel to provide tension on forward and rearward legs of the ladders to firmly retain the slats; and a second Venetian blind having a head channel secured to an upper portion of a window frame above the arcuate windows, the slats of the second blind being provided with notches at the ends thereof, and guide rails on each side of the window frame extending from the peak of the greenhouse to the bottom of the lowermost Venetian blind for supporting the slats of the first blind and the notched slats of the second blind. A horizontal sky light installation is also described.