Some Basic Principles of Dark Adaptation

Evaluation of Night Vision*

“…A simpler test would be to have either a test object of fairly large size and constant contrast which is viewed at varying levels of illumination well within the scotopic range, or to have test objects of varying size viewed at a fixed level of illumination also within the scotopic range. Measurements of dark adaptation8' 21 37 have shown that rod or scotopic vision covers a range of illumination of approximately 2.5 log , ,u 1 (flash threshold) to 5.5 log ,u ,u 1. Reference to Figure 2 shows that a Landolt C subtending a visual angle of 4 degrees (visual acuity 20/1000) can be seen at a level of illumination of approximately 4 log , u .…”