Blade for a wind turbine generator for converting wind energy into electric energy, comprising: - a blade structure longitudinally extending along a blade axis and comprising a blade tip, an opposite blade root, a longitudinal leading edge portion and a longitudinal trailing edge portion which are extended between the blade root and the blade tip; and - an outer aerodynamic shell defining an airfoil including an airfoil leading edge, an airfoil trailing edge and an airfoil suction side and an airfoil pressure side (28, 29) between said airfoil leading and trailing edges (26, 27); wherein said outer aerodynamic shell comprises a suction side panel and a pressure side panel which are made from a transparent material and are fastened to the blade structure so as to define the airfoil suction side and the airfoil pressure side (28, 29), respectively; wherein the blade comprises a suction side fastening seat and a pressure side fastening seat arranged on the suction side and pressure side of the blade, respectively, to fasten said transparent panels (31, 33) to the blade structure; wherein said blade comprises a transparent region between said transparent panels (31, 33) and wherein said transparent panels (31, 33) are arranged facing one another so that it is possible to see through the blade looking through said transparent panels (31, 33) and said transparent region; said blade being characterized in that: - the suction side panel and pressure side panel partially define the airfoil suction side and the airfoil pressure side (28, 29), respectively; - the longitudinal leading edge portion comprises a longitudinal tubular member, said longitudinal tubular member having a cross-section profile shaped as a closed loop comprising a pair of steps (71, 72) arranged on two opposite sides of the longitudinal tubular member to define said suction side and pressure side fastening seats; and - the longitudinal trailing edge portion has a cross section profile which is shaped essentially like an arrow. - a blade structure longitudinally extending along a blade axis and comprising a blade tip, an opposite blade root, a longitudinal leading edge portion and a longitudinal trailing edge portion which are extended between the blade root and the blade tip; and - an outer aerodynamic shell defining an airfoil including an airfoil leading edge, an airfoil trailing edge and an airfoil suction side and an airfoil pressure side (28, 29) between said airfoil leading and trailing edges (26, 27); wherein said outer aerodynamic shell comprises a suction side panel and a pressure side panel which are made from a transparent material and are fastened to the blade structure so as to define the airfoil suction side and the airfoil pressure side (28, 29), respectively; wherein the blade comprises a suction side fastening seat and a pressure side fastening seat arranged on the suction side and pressure side of the blade, respectively, to fasten said transparent panels (31, 33) to the blade structure; wherein said blade comprises a transparent region between said transparent panels (31, 33) and wherein said transparent panels (31, 33) are arranged facing one another so that it is possible to see through the blade looking through said transparent panels (31, 33) and said transparent region; said blade being characterized in that: - the suction side panel and pressure side panel partially define the airfoil suction side and the airfoil pressure side (28, 29), respectively; - the longitudinal leading edge portion comprises a longitudinal tubular member, said longitudinal tubular member having a cross-section profile shaped as a closed loop comprising a pair of steps (71, 72) arranged on two opposite sides of the longitudinal tubular member to define said suction side and pressure side fastening seats; and - the longitudinal trailing edge portion has a cross section profile which is shaped essentially like an arrow.