The relative spectral energy distribution of a tungsten ribbon filament lamp calibrated at 2854°K (C2 = 14 380) differs from that of a coiled filament type lamp operating at the same color temperature. There is reason to believe that the relative spectral energy distribution of the latter resembles more closely the relative spectral energy distribution tabulated by the CIE for that source and, consequently, lamps of the coiled filament type have been recommended for use as the standard. It has been shown theoretically that the difference between the two sources causes discrepancies in the chromaticities of certain test colors and it follows that the chromaticity coordinates of samples obtained by using the coiled filament lamp should be nearer the true values. The following paper describes an experiment in which ribbon and coiled filament lamps calibrated at 2854°K were subjected to visual and photoelectric tests to determine the significance of of the effect of the different energy distributions on selected test colors. An analysis of the results shows that small changes in chromaticity do occur, but for practical colorimetric purposes these differences can safely be ignored.
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