The luminances of equally bright colored lights are not necessarily equal when chromaticities of these colored lights are different. This is a crucial problem in the present photometry. The discrepancy between brightness and luminance is greater for colors with higher purities, as known as the B/L effect. In this paper, the amounts of test colors were adjusted so that these colors appeared equally bright to the reference white, and luminances of these colors were measured with flicker photometry. We used 191 test colors to cover almost the entire region of a chromaticity diagram including the purple region. The B/L value of each test, i. e., the ratio of the luminance (B) of the reference white to the luminance (L) of the test color, was obtained and used to plot constant B/L loci in the CIE 1931 (x, y) chromaticity diagram. It is shown that the constant B/L loci appear wider in the green region than the blue-violet region in the chromaticity diagram. This tendency is confirmed in general in similar experiments performed by other researchers, but the details in the shape and size of the loci are quite different among experiments, suggesting that more data are needed to establish the standard B/L function for the new photometry.
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