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An aqueous solution of cupric chloride, cobalt ammonium sulphate and potassium dichromate is a useful filter for modifying the spectral response of certain types of emission photocell, so as to match the response of the standard (photopic) eye This paper gives the spectral densities of various concentrations of these three substances, in water. From these, the concentrations of the three components required to make a correction filter for a given photocell, can be calculated An example of such a calculation is also given, and the practical performance of the filter is discussed.
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J. S. Prestón (1946) studied this question.
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