Regeneration after full bleaching is twice as fast when bleaching takes 1 sec as when it takes 2 min. This is not related to the photoreversal that may result from multiple quantum hits per molecule; nor with Villermet and Weale's change of photolysabiiity after sustained bleaching with very strong xenon light, for their results do not follow the equally strong bleaches with tungsten light used in this paper. The regeneration rate depends upon the amount of 11- cis retinal immediately available, and during a prolonged bleach this is largely exhausted. General equations are developed to describe the pigment kinetics in a wide range of conditions.