Black spectral responsivity.

Six subjects induced blackness within a circular broadband field by increasing the radiance of a surrounding monochromomatic annulus, which varied in wavelength. Between the central field and the annulus was a thin dark ring. Half of the subjects were instructed to increase the radiance of the annulus until the central field just turned black, and the other half were instructed to increase the radiance of the annulus until the contour between the central field and the dark ring disappeared. Spectral luminous efficiency functions measured by the methods of heterochromatic flicker photometry (HFP) and brightness matching (HBM) were determined for each subject and compared with the subject's blackness-induction functions. The hypothesis that the contour-disappearance instruction would yield blackness-induction curves best fitted by flicker photometric functions and that the absolute-blackness instruction would yield blackness-induction curves best fitted by HBM functions was not confirmed. There was only one subject for whom the spectral efficiency of blackness was represented better by HFP than by HBM. There was one subject for whom blackness spectral efficiency was fitted better by HBM than by HFP. For the remaining four subjects, there was no difference in fits.