The only real way that light could escape from the building, considering the precautions I took, would be light escaping from the thick curtains (I was thinking holy of holies style curtains several inches thick) then flowing outward through the gaps between the boards of the ship.  (considering the windows were already sealed)  Even at night, a full iconic can't be THAT visible when you're indoors and taking every precaution to keep it under wraps.