Binocular color fusion limit.

When two lights of different wavelengths are dichoptically presented to the eyes to form a single visual field, the fusion of colors cannot be assured unless the difference is relatively small. The limit of the wavelength difference delta lambda beyond which no homogeneous color is obtained was determined for the wavelengths covering a range of about 500 to 660 nm. It varied from about 10 to 50 nm depending upon the wavelength region investigated, which is much larger than the delta lambda values normally obtained in wavelength discrimination experiments. The limit was also obtained for a pair made up of a white light and a colored light that varied in purity. The value was again quite large. These results suggested that the tolerance for color difference is fairly lenient as far as binocular color fusion is concerned.