The differential limen for matching spectral colors by subjects with normal color vision

The amount of error made by 21 subjects with normal vision in matching a color band of given intensity was determined for different points on the spectrum. The subject looked into a spectrophotometer and matched the color seen there with a color (determined by his adjustment) seen in a spectrometer. The error was determined in terms of the deviation of Ångström units between the standard and the produced color. "A marked tendency to under-estimate green was noted at lowered intensities. In the longer wave lengths the reverse holds true. These curves cross at about 5600 Å, which is near the theoretical point of maximum effect on the human eye . . . the curves tend toward parallelism between this point and 5879 Å in the spectral range." Detailed data on the tendency toward over-estimation or under-estimation for various colors and for different intensities are reported.