Patent ID: 6097451
Filing Date: 2000-08-01
Classification: A61F,G02F

Abstract:
A liquid crystal shutter construction (18), suitable for a glare shield or a welding glass filter, which shutter construction is able to switch between a high light-absorbing dark state and a low light-absorbing transparent state, and vice versa, in response to an electric signal and which includes two nematic-type liquid-crystal cells disposed between transparent, electrode-loaded plates connectable to a voltage source (22) and which cells are provided with coatings treated to define the direction of molecule alignment at their mutually facing surfaces, whereby a mutual angular displacement between said plates causes the liquid crystals to form a twisted helix structure in the absence of a voltage between the electrode coatings on the plates, wherein the cells are each mounted between mutually extinguishing polarisation filters, and wherein the molecule alignment directions are turned so as to obtain a compensation effect between the respective asymmetrical light absorptions of the two cells when a voltage is applied, wherein at least one of the twisting angular displacements of the cells between said molecule alignment directions differs from 90.degree., the shutter construction comprising means (20) for generating a variable cell driving voltage applicable to said electrode-loaded plates, said means (20) being devised to produce a cell driving voltage higher than twice the threshold voltage for at least one of the liquid crystal cells and with a polarity switching frequency of less than 1 Hertz.