Abstract
LIGHT which falls on a photographic plate causes the crystals of silver halide, which form the essential constituent of the sensitive layer, to be converted by subsequent development to silver grains, and gives rise to a blackening of the exposed areas. The silver grains can be counted under the microscope, but they provide no direct measure of the incident energy. Although much painstaking work, culminating in the recent theory of Gurney and Mott, has led to a fairly complete understanding of the mechanism of the photographic process, many factors enter in to prevent the establishment of a one-to-one, or other simple, relationship between silver grains and absorbed quanta. Thus the photographic plate cannot be used as a method of absolute measurement of radiation: like the part played by the eye in visual photometry, its role is that of a null instrument for the measurement of an unknown source of radiation by comparison with a known. In addition, and unlike the eye, it provides a permanent record of brightness variations, often over an extended field.
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DAVIES, E. ROLE OF PHOTOGRAPHY IN THE DETECTION AND MEASUREMENT OF RADIATION. Nature 149, 430–432 (1942). https://doi.org/10.1038/149430a0
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DOI: https://doi.org/10.1038/149430a0