Bunsen-Roscoe law

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A basic principle of photochemistry according to which the reaction of any light-sensitive pigment, including a visual pigment in the retina of the eye, is a multiplicative function of the intensity of the light exposure and its duration, the photochemical effect on pigment molecules depending simply on the total number of incident light quanta. It is usually expressed as I × t = k, where I is the physical intensity of the flash, t is its duration, and k is a constant. It is valid up to about 100 milliseconds for absolute thresholds and difference thresholds or just noticeable differences in visual sensations, and is valid over a far wider range of durations for photographic emulsions. Also called Bloch's law. [Named after the German chemist Robert Wilhelm Eberhard Bunsen (1811–99) and the English chemist Henry Enfield Roscoe (1833–1915) who formulated it]

Subjects: Psychology.

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