A Physical Comparator for the Color Temperatures of Incandescent Lamps*

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Abstract
An apparatus has been assembled and is presently being used to evaluate the color temperatures of incandescent tungsten lamps by physical comparison techniques. A red-to-violet ratio method of establishing the effective slope of the radiometric function is utilized. The apparatus uses a single 931-A photomultiplier to receive radiations from the “standard” and “unknown” lamps through red and violet filters sequentially. Resultant oscilloscope patterns are judged for equality. Accurate results can be obtained in a short period of time, thus permitting large quantities of lamps to be calibrated with a minimum of effort.