The effect of exposure to sunlight on night vision.

Reports from North Africa and the South Pacific during the last war suggested that night vision deteriorates after exposure to very strong sunlight, particularly on coral islands. Derman (also reference 7) re­ ported SO cases of night blindness in the Turkish army, apparently due to bright light. In view of the military importance of this problem, it was decided to investigate the effects of sunlight in a quantitative manner. The problem is a three-fold one. First, is the onset of dark adaptation delayed after ex­ posure to bright sunlight? Second, is the process slowed up so that the threshold is still above normal even after an hour or two in darkness? Third, is the effect of daily exposure cumulative? The first question has already been an­ swered. The speed of dark adaptation is strongly influenced by the brightness of the preceding light adaptation.· 4 · 1 0 Thus, after light adaptation to 100 millilamberts (ml.), the rod portion of dark adaptation appears almost at once, whereas after exposure to