Red and green signals within the chromaticity limits proposed by Judd, shown in a previous study to be satisfactory for instru¬ment-panel lights, are confused by many color-deficient subjects when the signals are of very small angular subtense (i.e., “point sources”).nAbility to differentiate red and green point sources within the specified chromaticity limits varies with the illuminance of the stimu-lus and with the degree of defect of the color-deficient observer.nFor illuminances of about 20 mile-candles the currently used passing score of 50 on the Color Threshold Test qualifies only those who can distinguish red and green point sources fall¬ing within the chromaticity limits specified by Judd.
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