Samenvatting
The values of the relevant factors which determine the visibility of a stationary object to a test-subject have been measured for threshold situations bordering between visibility and invisibility of the test-object. In this way the visual power of test-subjects has been expressed in a threshold-relationship between the four factors D ( the size of the detail to be distinguished ) , C ( the luminance contrast between the object and its surroundings) B ( the luminance of the field of view) and t ( the time during which the object is exposed to view). The objects used were Landolt rings, darker than the surroundings.