Reversibel veraenderbare optische Filter

1,105,515. Photo-electric systems. INTERNATIONAL POLAROID CORPORATION. March 9, 1965 [March 9, 1964], No.9959/65. Heading G1A. [Also in Divisions E1, F4 and G2] A photo-electric cell 12 may be used to govern the intensity of a variable colour filter device 1, which, as shown in Fig. 1, comprises two electrically conducting glass-electrodes 2, 3, an electrolyte 5 and a layer of non-migratory material 4 which reacts with migratory material (e.g. ions) to provide a reversible change in spectral absorption on passing an electric current, the density of colour being increased or decreased depending on the direction of the current the direction being governed by the photo-electric cell. Modifications of the filter device 1 employing two layers of material 4, and three electrodes Figs.2, 3 (not shown) may be used. The non- migratory material may be a polymer containing groups which change colour on change pH, oxidation/reduction or salt formation induced by the electric current. The filter may be incorporated in camera-shutters, windows, and vehicle headlamps the photo-electric cell being motivated by the incident light, to maintain the transmitted light at a required level in the case of the window and shutter, or reduce glare in the case of the head-lamp.