Filters for the reproduction of sunlight and daylight and the determination of color temperature/

A large number of filters, as listed in the introduction of the paper, have been developed for use in photographic sensitometry, colorimetry, and photometry.They are reproducible from specification and may be prepared in the laboratory.They consist of a 2-compartment cell with three borosilicate crown glass win- dows, the two compartments being filled, respectively, with solutions A and B, having compositions as follows: Solution A Copper sulphate (CuS0 4 .5H>0)g__ c Mannite (C 6 H 8 (OH) 6 ) g_ _ c Pyridine (C5H 5 N) cc__ 30.Water (distilled) to make cc__ 1,000 Solution B Copper sulphate (CuS0 4 .5H 2 0) g__ Ci Cobalt ammonium sulphate (CoSO^NH^SO^H^O^g-.c 2 Sulphuric acid (specific gravity 1.835) cc._ 10.Water (distilled) to make cc__ 1,000The values of c, Ci, and c2 vary from one filter to another.The design of the filters has been based upon extensive spectrophotometrie measurements of the component solutions and cell, including a study of Beer's law over the ranges of concentrations used, and upon methods of computation giving accurate color matches and relatively good spectral energy matches between the source-and-filter combination and the energy distribution which it was sought to duplicate.Detailed studies have been made of the reliability of the data, the spectrophotometrie reproducibility of the chemicals, the permanence of the solutions, their temperature coefficients, and various other factors of importance in the preparation and use of the filters.The paper contains 33 figures and 26 tables, giving among other things the energy distributions and fundamental spectrophotometrie and colorimetric data used in the computations, auxiliary spectrophotometrie and colorimetric information obtained during the investigation, and the trilinear coordinates of the various source-and-filter combinations and of the Planckian radiator from 1,600°to 20,000°K.computed on the basis of the adopted mean sun as the "neutral" stimulus.The filters are further described in 38 charts, each chart giving the chemical formula, the spectral transmission, and the light transmission of the filter, as well as the spectral energy distribution of the source, that of the source and filter combined, and the energy distribution which serves as the ideal in that particular case.