Measurement of rod and cone effects in mesopic visual sensitivity by varying viewing field.

To investigate the effects of rods and cones in mesopic visual sensitivity, we perform spectral sensitivity experiments by varying viewing fields and adaptation levels. We obtain mesopic spectral sensitivities for 2° and 10° centrally viewing fields and a (10°-20°) peripherally viewing field at adaptation luminance levels of 0.04 cd/m², 0.4 cd/m², and 1.8 cd/m². The spectral shapes are examined through comparison with the Commission International de l'Eclairage luminous efficiency functions. We observe a decrease of visual sensitivity with an increase of adaptation luminance and the dependence of visual sensitivity on viewing field. The observation is discussed in terms of the interaction between rods and cones.