PROBLEM TO BE SOLVED: To provide a system for improving scotopic vision consisting of a photoradiation method for improving the visibility and a target when a person acts in a dark place and when the person detects, confirms and observes a target by visual sense.SOLUTION: Light 6 with a wavelength being hard to perceive and exerting no influence on light adaptation and dark adaptation is applied, and the visibility is improved by self-luminescence of a target 3 having a substance activated by receiving the light. The photoradiation method and an irradiation device 1 applies light with a wavelength being hard to cause light adaptation and requiring a short time to cause the dark adaptation. The light is defined as a light source for perceiving another target 3.
