GB666009A - Improvements in or relating to colour temperature meters - Google Patents

Abstract

666,009. Measuring colour temperature. SANGAMO WESTON, Ltd. June 30, 1949 [Dec. 31, 1948], No. 17369/49. Class 40 (iii). In a system for measuring colour tem. perature for photographic purposes, adjustment of the relative illumination of a blue. sensitive and a redsensitive photo-cell to balance a bridge circuit of which each cell form, an arm, is effected by a shutter carried by an instrument pointer, the pointer then indicating the colour temperature directly. As shown, photo-cells BT and RT, sensitive respectively to blue and red light and each connected to a battery B, are illuminated through an aperture W by the source. Manual adjustment of a pointer P carrying the shutter O reduces the light reaching one cell and increases that to the other until balance is indicated by a galvo G connected across the cell and battery junction. If the illumination intensity is small condenser C may be charged when closing of switch S will indicate out-of-balance on the galvo. A filter F coinpensates for the greater sensitivity of the red cell to balance the circuit at a predetermined colour temperature and eliminates an output peak in the blue part of the spectrum.