The Scotopic Visibility Function

Abstract

The scotopic (dark-adaptation) visibility of radiation through the spectrum has been determined for fifty observers under 30 years of age. A modified photometric matching method was used at a very low brightness (3×10-6 candles/ft2 or 3.2×10-9 stilbs). A subsidiary investigation showed that the ultimate scotopic curve was approximated closely. Another demonstrated the effect of age, showing a progressive decrease in sensitivity at the blue end of the spectrum with increasing age, the effect first becoming noticeable at about 30 years of age. A detailed comparison of the present results with those of previous workers is made and reasons for discrepancies are discussed.