This study was performed to determine significant light wavelengths to improve color discrimination ability of subjects with deutan. We conducted both the Ishihara test and the Farnsworth Panel D-15 test for subjects with deutan and normal color vision. Seven different LED lights from 450 to 660 nm and an additional D65 white lamp were utilized to change the lighting conditions, including the wavelength and intensity. The results of the Ishihara test and D-15 test showed that color identification of deutans was markedly improved with the longer wavelength LEDs regardless of the intensity of the additional D65 lamp. Notably, the error rates of deutans in the Ishihara test were < 25% for LED wavelengths of 630 and 660nm. In the case of subjects with normal color vision, the D65 lamp abolished the errors in the Ishihara test, regardless of the LED wavelength. Addition of the D65 lamp also decreased the number of crossings in the D-15 test. These results suggested that illumination by LED light with longer wavelengths, such as 630 and 660nm, may provide deutans with greater red-green discrimination ability in both the Ishihara test and the Farnsworth Panel D-15 test. (C) 2016 Wiley Periodicals, Inc.