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Abstract:
Some twenty years ago Hecht, Shlaer, and Pirenne (1942) found that the minimum energy required for threshold vision of the human eye yields values between 2.1 and 5.7 · 10-10 ergs at the cornea, which correspond to between 54 and 148 quanta of blue-green light. Taking into consideration the energy losses due to corneal reflection, absorption in the optic media, and retinal transmission, the range of 54 to 148 quanta at the cornea becomes as an upper limit 5 to 14 quanta actually absorbed by the retinal rods. Obviously the number of 500 rods involved precludes any significant two quantum absorptions per rod. In order to produce a visual effect, one quantum must be absorbed by each of 5 to 14 rods in the retina; a coincidence of 5 to 14 primary events is necessary for the elicitation of a visual effect.
