Spectral Energy Thresholds for the Resolution of Acuity Targets*

Threshold relative energy measurements have been made with monochromatic light at 10-mμ intervals between 400 and 710 mμ for threshold criteria which represent a series of visual acuities in addition to light detection. The data can be approximated by summing cone and rod sensitivities derived from earlier independent measurements of light detection by the dark-adapted eye in the fovea and the periphery. The relation between the logarithm of threshold energy and visual acuity required by the criterion of threshold has been predicted from monochromatic energy data for several broad spectral distributions of illumination and predictions are compared with empirical data.