Bunsen-Roscoe Law

BUNSEN-ROSCOE LAW (Bunsen-Roscoe), expresses the dependence between the photochemical effect and the amount of radiant energy causing it. Based on experiments with Cl and H, which under the action of light form hydrogen chloride, Bunsen and Roscoe concluded that the amount of reaction product depends only on the intensity of the incident radiant energy and the time during which the reaction proceeds. Further experiments showed that a similar dependence is also observed in other photochemical reactions: the amount of reaction products is always directly proportional to the amount of absorbed energy. Thus, if J is the intensity of the incident light and t is the time of its action, then the photochemical effect will be the same if the product J·t is constant. Subsequently, a number of cases were discovered in which the B.-R. law proved inapplicable. Thus, for a photographic plate, the law was established: J·t^p = constant, where p<0 (Schwarzschild's law). The latter circumstance must be taken into account when the blackening of a photographic plate is used to measure the intensity of light.