Reciprocity (photography)
IN PHOTOGRAPHY, THE INVERSE RELATIONSHIP BETWEEN THE INTENSITY AND DURATION OF LIGHT THAT DETERMINES THE REACTION OF LIGHT-SENSITIVE MATERIAL
Reciprocity failure; Schwarzschild effect; Reciprocal failure; Schwarzschild law
In photography, reciprocity is the inverse relationship between the intensity and duration of light that determines the reaction of light-sensitive material. Within a normal exposure range for film stock, for example, the reciprocity law states that the film response will be determined by the total exposure, defined as intensity × time.