TIME AND INTENSITY IN PHOTOSENSORY STIMULATION

In its photosensory effect, the action of light depends on two variables,—intensity and time. If the intensity alone is varied, the photochemical effect is proportional to the logarithm of the intensity. If the time alone is varied, the effect is proportional to the time. Experiments here reported show that when both the intensity and the time are varied, the photochemical effect is equal to the product of their separate activities: E = kt log I. These results furnish the means of expressing directly the relation between the intensity of illumination and the reaction time of Mya.