A Fundamental Study to Investigate the Effectiveness of Flashing Light as Visual Signal

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In this study, the effective intensity of a monochromatic flashing light was measured by changing color, intensity and flashing duration of a light, and background luminance.The effective intensity, Ie, which was obtained by visual experiment, was compared with calculated effective intensity, Is, by Blondel & Rey-Douglas's formula.When the background luminance is O[cd/m^2] and the intensity of the flash is at threshold level, the Ie/Is is substantially greater than 1 for the flash of short time duration.As the duration becomes longer, the Ie/Is decreases monotonously and gradually approaches 1.As the intensity rises to the low or medium level, the Ie/Is decreases once as the duration increases from 100[mus] to 6[ms], and increases within the duration of 6 to 50[ms]. For the duration over 50[ms], it decreases again and approaches 1 gradually.Therefore the time durations at which the Ie/Is takes minimum and maximum value exist.When the background luminance is raised to 1 or 10[cd/m^2], the Ie/Is takes minimum and maximum even at threshold level.These durations are related to the response time of the visual system, and are shortest for the white flash, followed by blue, yellow, green and red.In addition, for the flash of short duration, the effective intensity of the red flash is the highest, and becomes lower in the order of white, yellow, green and blue.In particular, the flash with duration of shorter than 1[ms], which has higher effective intensity than the estimated value, is superior as visual signal for its brightness and conspicuousness.