Diurnal variation of hue discriminatory capability under artificial constant illumination

Diurnal variation of hue discriminatory capability under artificial constant illumination of 4000 lux was studied with 10 young female adults using the 100-hue test. There were conspicuous diurnal variations in the yellow-blue and red-green systems, with marked reductions of error score in the evening. However, observations of the blue, yellow, green and red systems separately disclosed that there existed clear diurnal rhythms in the blue and green systems, but not in the yellow and red systems. This suggests the existence of diurnal variation in function of the S and M cones responsible for the blue and green hue.