Abstract

Using the method of adjustment and a panel of 256 LEDs (dominant wavelength 640 nm) mounted in a solid, black enclosure and covered with a white diffusion screen, we measured CFF to cone stimuli (sinusoidal luminance modulation of 30%) across the temporal visual field at three different levels of retinal illuminance (1970,123, and 25.0 phot, td) produced by inserting neutral density filters (Lee) in front of the panel. Retinal illuminance was constant at all eccentricities studied because retinal area per one solid degree of visual field and effective pupillary area decrease similarly when eccentricity increases from 0° to 80°. The stimuli were M-scaled¹ to keep the number of ganglion cells stimulated at various eccentricities approximately constant (4400 cells). M-scaling was obtained by reducing the viewing distance in inverse proportion to the sampling density of ganglion cell receptive fields across the retina. CFF was found to increase monotonically with eccentricity but the increase was the steeper the higher the level of retinal illuminance, in agreement with our previous results.² However, when plotted in double logarithmic coordinates, CFF was found to increase as a single linear function of photopic luminous flux (F) collected by retinal ganglion cells: CFF = 18 × F^0.22 (r² = 0.945). Flux was calculated by multiplying retinal illuminance with Ricco's area that provides an estimate for the average area of the human ganglion cell receptive field center at various retinal locations.

© 1989 Optical Society of America