Abstract

It was hypothesized that a field delivering an equal quantal flux at all visible wavelengths to the retina would provide a neutral background for measuring photopic spectral sensitivity. Foveal detection thresholds were measured for monochromatic lights ranging from 440 to 640 nm on backgrounds of different spectral composition. One-degree test fields were flashed for 1 s every 5 s on the following backgrounds: a field with the spectral characteristics of a 1000-W xenon-arc lamp; a field approximating source A of the International Commission on Illumination; a field equivalent to one delivering to the retina an equal quantal flux at all visible wavelengths; a monochromatic field of 470 nm. Backgrounds were presented at 10 and 1000 trolands. Spectral sensitivity determined on each of these backgrounds was compared with that measured in the dark. A background was considered to be neutral if the shape of the spectral sensitivity curve produced with it was (1) invariant with changes of the intensity of the background and (2) matched that from the dark-adapted condition. The equal quantal background came the closest to fulfilling these criteria. For both observers in the experiment, such a background appeared predominantly blue.

© 1986 Optical Society of America