| 摘要 |
A multiple layer protective glass, particularly a protective glass for a welding shield, for damping the light transmission, the layers of which are in turn comprised at least of a first polarizer, a first electrooptical cell, a second polarizer, a second electrooptical cell and a third polarizer, the electrooptical cells consisting of liquid crystals enclosed between transparent parallel plates coated with electrically conducting layers, said crystals being arranged in their non-excited condition to form a helically twisted structure for rotating the plane of polarization of the passing polarized light. The planes of polarization of the first and the second polarizer (2,4) are at right angles to each other. The planes of polarization of the second and the third polarizer (4,6) enclose an angle which is between 0 DEG and 60 DEG . The angle of rotation of the helical structure formed by the liquid crystals in the second electrooptical cell (5) is between 90 DEG and 30 DEG and the said angle and the angle of rotation are complementary angles. Means (13) are provided for exciting the two electrooptical cells (3,5) in opposite modes by the application of a voltage between the conducting layers (10a,11a; 10b,11b) of the electrooptical cell. |
