Comparison of scotopic, mesopic, and photopic spectral sensitivity curves.

Spectral sensitivity curves have been established for the ten-degree periphery throughout a range of intensities from absolute scotopic threshold to a level five log units above threshold. Surround conditions included adaptation of the eye both to complete darkness and to the light level under investigation. In addition, foveal curves have been established at one level under the same experimental conditions as the peripheral curves.The results show that there is no large shift in the curves toward the longer wavelengths with increasing intensity until a level five log units above threshold has been reached, and that, even at this point, the peripheral curve does not approach the spectral sensitivity found in the foveal curve. While the curves retain the predominant scotopic element, that is, sensitivity to the shorter wavelengths remains basically unchanged, sensitivity to the longer wavelengths does increase throughout the entire range of intensities investigated. This is true for both surround conditions; in addition, a slight increase in sensitivity to the long wavelengths and better brightness discrimination are found with the lighted surround.