Saturation Scale for Yellow Colors*

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Abstract
The relationship between colorimetric purity of the stimulus and saturation of the color evoked under specified observing conditions has been determined for yellow colors by using the yellow series of Lovibond glasses (dominant wave-length about 575 mµ). Two observers have selected glasses from this series requisite to produce a scale progressing by equal steps from white to yellow. The step size varied from something approaching the least perceptible in one determination to about four times that size in another; it was found that this variation produced no significant change in the shape of the curve connecting purity and saturation. An increase in step size by an additional factor of three was tested for five observers. It was found chiefly to introduce greater individual difference; the average for all observers was not significantly changed. It is concluded that the integral of the sensibility to purity change from zero purity may safely be taken as the saturation of the yellow color evoked under the present observing conditions. The saturation-purity curve resulting from these determinations is compared with that from previous experimental data and with those from two empirical relations. In order to discover whether the discrepancies revealed by this comparison are ascribable to individual difference, groups of glasses representing each of four curves compared were selected and judgments obtained from eight observers with the result that the experimental scale was corroborated. The individual differences shown among these eight observers were too slight to account for the discrepancy. It is concluded that an empirical relation which was previously found fairly well justified by data on other types (wave-length, color-temperature) of chromaticity sensibility, though not perfect, yields a saturation scale for yellow which is close to the true one.

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