Apparent Hue of the Road Traffic Light Signals in the Daytime, at Dusk and in the Nighttime

Abstract

Apparent hue of the road traffic light signals was investigated employing the colour naming method in the daytime, at dusk and in the nighttime. Five subjects with normal colour vision participated inthis experiment. The recommended colour boundaries in the chromaticity diagram for the traffic light signals in japan are different from the CIE recommendation especially for the green signals.
The results showed that apparent hue of the green traffic light signals ranged from greenish-blue to yellowish-green and considerable number of signals deviated from the CIE recommendation. Hue shift ofthe green traffic light signals at dusk and in the nighttime was also pointed out, that is, blue and white components of the green light signals increased considerably in the mesopic and scotopic visual environments. This suggests that apparent hue of the traffic light signals changes according to the adaptation levels of car driver's visual systems. The green lightsignals in the future were considered from the results of this experiment.