Reciprocity Relations

Heisenberg uncertainty relation (1927) Bunson-Roscoe law: In a phototropic reaction, the product of time t and intensity I (thus the energy amount of the used light) corresponds to the stimulus strength. R = I × t It is of no importance whether a light stimulus of low intensity is applied for a longer period of time or whether a stimulus of high intensity is applied for a short time. (Bunsen: 1811-1899).

• Bloch's Law: A similar reciprocity in the visual system.
  Under about 100 milliseconds (1/1000 of a second) stimulus duration it is possible to exchange the amount of light for the duration and maintain a constant effect.