The Visibility of Point Sources as a Function of Background Luminance, Target Luminance, Eccentricity, Wavelength, and Flicker Rate

Abstract

Abstract : The existing visibility literature was reviewed to determine how thresholds for detection of point-source targets vary as a function of target luminance, wavelength, eccentricity, and flicker rate as well as background luminance. After reviewing over 1500 papers and/or abstracts dealing with the above parameters, data from 14 studies were converted into a common luminance metric (cd.m-2), adjusted for target size, and grouped into four luminance ranges (scotopic, low photopic, and two higher photopic ones), three eccentricity ranges (centered around 0 deg, 30 deg and 60 deg), and CW and three flicker ranges (1-2 Hz, 3-4 Hz, and 8-12 Hz). The results of the review showed that contrast thresholds decrease from ~25% at scotopic levels to around 2% at higher photopic levels. Thresholds increase by 2-3 log units from the fovea to 60 deg off-axis, except at scotopic levels where sensitivity is relatively flat across eccentricity (and even slightly lower at 30 deg off-axis). Thresholds for flickering targets were slightly lower (by 0.5 log units) than for static ones, with the optimal flicker rate dependent on luminance (e.g., sensitivity is best for lower flicker rates at low luminances but is best for higher frequencies at high luminances). Aside from wavelength, whose effects can be modeled by means of the v-lambda (photopic) and v'-lambda (scotopic) spectral sensitivity curves, the two biggest influences on visibility by far are background luminance and eccentricity.