Blue Lobe Research Articles

A colorimeter for pyrotechnic smokes

A tristimulus photoelectric colorimeter has been designed to measure the chromaticities of pyrotechnic smokes having highly saturated colors. To obtain a compact housing for three multiplier phototubes, “head-on” type (RCA 5819) phototubes are used. For high sensitivity and stability the photometric units are three Photovolt Multiplier Photometers, Model 520-M. To minimize edge effects and rear wall reflection, the smoke chamber was designed as a 36-inch cube. The chamber is illuminated by four 150-watt flood lamps placed to yield uniform illumination on the viewing window. Three filters were designed to approximate the daylight CIE standard observer functions for the source-filter-phototube combinations of the instrument. As the CIE y¯ and z¯ functions are unimodal, little difficulty was encountered in designing the filters to approximate these functions. The CIE x¯ function, which is bimodal, required a divided filter to approximate its two lobes. The filter constructed was composed of two sectors, one approximating the “blue lobe,” the other approximating the “red lobe,” of the x¯ function. Satisfactory results have been obtained with this colorimeter using Munsell papers as standards.