夜間視力と光と影との関係

Night Vision and Relations of Light and Shadow

Night vision differs greatly according to one’s position relative to a luminous body and shadow: When a luminous body, such as the moon, is faced, vision is decreased. When the light is behind, vision is increased. When a luminous body is overhead, the mean of increase and decrease is the same. Even though facing the light, if it does not strike the eyes directly, it injures vision but little. One can see when looking from darkness into light, but not when looking from light into darkness. While holding the light yourself, only your own surroundings can be seen. When a light is behind an object, the latter’s outlines are clearly visible. A black object or a moving object covered by shadow, is difficult to see. Small objects seem far away, and large ones seem near. Bright objects appear near, and obscure ones, far away. The above facts teach one that, when covered by dark objects, or when moving in the shadow, to look at the bright side from the dark as much as possible, and not have the light directly in front.