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1950
EFFECTS OF COLOR TEMPERATURE
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Moon6 says, in the report of the Optical Society of America Committee on Colorimetry : " ... the concept of color temperature . . . still serves as a rough engineering specification. However, one may expect it to decline gradually, to be replaced by the much more satisfactory spectrophotometric curve and by the colorimetric methods of Chapter XIII."
To this, Jones and Condit7 add the following comment in a recent paper before the Optical Society of America: "Our feelings are somewhat stronger than those of Moon concerning the discontinuance of the usage of the term 'color temperature/ particularly in the field of photography. We should like to recast the last sentence of the above quotation to read as follows : 'However, we hope its use in the field of photography will decline rapidly or cease abruptly and be replaced by... etc."
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Fig. 2. Two monochromatic lines, at 470 and 573.1, visually match Illuminant C but would photograph as pronouncedly blue, as shown by dotted trichromatic filter curves.
Fig. 3. Two monochromatic lines, at 490.4 and 610, visually match Illuminant C but would photograph as red.
Our own work in the field of illuminant color measurement has made us extremely conscious of the shortcomings of Kelvin temperature, which has led us to seek something more descriptive.
The inadequacy of visual-match color-temperature as a standard for color photography can be best shown by taking a few extreme cases. In Fig. 2 is shown the spectral distribution of a light source which emits two monochromatic lines, as shown. Colorimetrically, this is a visual match for Illuminant C, the artificial daylight of colorimetry. Photographically, as shown by the three filter transmissions indicated in dotted lines, this illuminant would photograph as a bright blue. The source shown in Fig. 3 would photograph as bright red, yet visually it matches Illuminant C. Lastly, that shown in Fig. 4 also matches Illuminant C, and would scarcely record on normal color film at all.