When the number of cells (cones at eccentricities 0-10 deg and ganglion cells above 10 deg) stimulated at various retinal locations was kept constant by enlarging the stimulus area with increasing eccentricity in the temporal visual field (M-scaling), CFF to red stimuli with dark surround increased as a single function of photopic luminous flux, collected by ganglion-cell receptive-field centres and calculated by multiplying Ricco's area with retinal illuminance at each eccentricity studied. The increase of CFF with the logarithm of photopic flux could be best explained by the Collins logarithmic law, the Kelly square-root law was almost equally good and the Ferry-Porter law was poorest. Adopting the general formulation of Corwin and Dunlap (Vision Research, 27, 2119-2123, 1987) the exponent of CFF is 0, 0.5, and 1 for the Collins, Kelly and Ferry-Porter laws, respectively. The exponent that best explained our results was found to be 0-0.3.