GB909342A - Improvements in or relating to a device for controlling light transmission or reflection - Google Patents

Abstract

909,342. Automatic light-intensity control systems. EASTMAN KODAK CO. Feb. 2, 1959 [Feb. 3, 1958], No. 3617/59. Class 38 (4). [Also in Group XX] A device for controlling light transmission or reflection comprises an electrolyte container 10 having windows for passing light 21 through the container, a transparent electrode 12 in the electrolyte 11 and positioned in the path of the light through the container, an electrode 14 in the container positioned so as not to interfere with the light traversing the container, and means for applying D.C. across the electrodes 12, 14 to plate or deplate the electrode 12 and thus control the light transmitted through or reflected by the electrode 12. A photo-electric cell 22 operates a switch 27, e.g. by means of a meter-type switch, Fig. 3 (not shown), which on being closed operates one or other of two solenoids to close the switch 27 to apply the appropriate polarity to the electrodes 12, 14. The container 10 may be wholly transparent and the electrode 12 may comprise a coating tin oxide, cadmium oxide, indium oxide, gold or gold-bismuth oxide on a glass or plastic plate 13. The electrode 14 may be a rod, plated with gold, or a ring, or it may be a grid or mesh of fine wire overlying the electrode 12, and it may be an inert material, e.g. carbon, or one contributing ions to the electrolyte, and the electrode 14 may be positioned to apply an uneven plated deposit on the electrode 12. The surface of the plate 13 may be planar or curved and may be sand-blasted or pebbled or be formed with specially arranged reflecting surfaces. Electrolytes mentioned include copper perchlorate with 10% perchloric acid, acid zinc sulphate, lead nitrate, silver nitrate and silver cyanide, and buffering agents, gelatine (to increase the viscosity), ethylene glycol and dyes may be added. Chemicals, e.g. HCL, may be added to the electrolyte to remove the metal deposit as it is plated on the electrode 14. In a modification, Fig. 4, the inner face 52 of one of the windows 51 forms the transparent electrode, the other electrode being 53. The device may be operated using visible light or U.V. or I.R. radiation, and applications mentioned include light filters, e.g. in vehicles or in time lapse photography and electro-optical memories. The thickness of the electrolyte layer may be 10<SP>-3</SP> inches or as little as 1 Á. Surface resistances and optical densities of the electrode 12 are quoted, and an operating voltage of 1.8 and current densities of 1 to 100 milliamps per square cm. of electrode are mentioned.