The spectral sensitivity of the 1° fovea of the right eye of two practiced observers was measured at 10 mμ intervals from 400 mμ to 700 mμ for the dark-adapted state and for the bright-adapted (10mL), chromatically neutral state. Ten complete luminosity functions were obtained for each observer for each of the specified adaptations. The data of these experiments are intended to provide controls against which to evaluate luminosity data for different chromatic states. A number of inflections and shoulders are found in the functions for both states of adaptation. Moreover, the functions for both observers are shown to undergo a change in form and a displacement from the bright to the dark-adapted state. These changes in the foveal functions, although small in magnitude, are in the same sense as the familiar “Purkinje shift.” Alternative theoretical explanations of the data are discussed and analyzed.
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