The effect of area on the critical flicker threshold.

The relation between the luminance required to discriminate flicker of constant rate (critical flicker threshold) and the size of theretinal area stimulated was determined under photopic conditions. At small stimulus fields (diameter less than 44 min of arc) the slope of the critical flicker threshold vs. area approximated to Riccò's law [log (I-A) = constant]; with larger fields (diameter up to 116 min of arc) the slope approximated to Piper's law [log (I-square root A) - constant].