Neutral points have been found by means of a rotary mixer and Munsell papers, minimizing any dispersion of individual values by individual ocular pigmentations. Determined thus, the Illuminant C values for 39 new (post-Walls-Mathews) protanopes covered a range of 3.7 mμ with the mean at 492.3 mμ, those for 38 new deuteranopes a range of 5.8 mμ with the mean at 498.4 mμ.
Illuminant D values for 13 additional protanopes covered a range of only 3.3 mμ with the mean at 490.3 mμ, those for 15 recent deuteranopes a range of only 5.1 mμ with the mean at 496.2 mμ. The intergroup gap, observed earlier by Walls and Mathews and also here with “C” values, is clearly genuine so that it is possible to diagnose protanopia and deuteranopia differentially from the neutral-point measurement alone (contrary to universal belief).
Evidence is presented that Illuminant D is certainly not “too blue” to be considered a physiological white standard, and that by comparison Illuminant C is really yellowish, so that Illuminant D is the better of the two to use in physiological investigations. This supports the earlier conclusion of Walls and Mathews based on color-normal subjects.
© 1956 Optical Society of AmericaFull Article | PDF Article
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