Abstract
At a crossing in a road, we have often found that the go-signal called as a “blue signal” does not appear blue, sometimes they are rather green. Such an inconsistency of the designation with the apparent hue of the signal light is an undesireble visual environment. The recommended color boundaries in the chromaticity diagram for the light signals of road traffic control in Japan are considerably different from the CIE recommendation especially as concerns the “blue signal”. The apparent hue of the lights in that “blue” region has never been evaluated quantitatively. We investigated the hue of those lights employing the color naming method for 3 subjects. The results showed that most of the lights are not blue, but greenish-blue or bluish-green. They are not psychophysically unique hues. The same method was used to evaluate the apparent hue of the “blue signal” s in the city road. Resulted responses pointed out that a variety of hues, from pure blue to yellowish-green, are existed. Because a blue light has some disadvantage for signal light considering the characteristics of our color visual systems, the green light and the term “green signal” should be most suitable for the traffic control signal.
