Influence of Stimulus Duration and Area on the Spectral Luminosity Function as Determined by Sensory and VECP Measurements

Abstract

Spectral luminosity functions were determined by measuring the radiation power of monochromatic test lights of 2° and 10° in diameter during exposure to white light of 30, 000 td. Criterion was (a) the achromatic threshold, (b) the chromatic threshold, (c) a small constant amplitude in the visually evoked cortical potential (VECP). With a test light duration of 10 ms the achromatic threshold exhibited a spectral luminosity function similar in shape to the CIE Vλ-curve, except for a slightly increased sensitivity in the shortwave region of the spectrum. Using the chromatic threshold as index, a general loss of sensitivity was found, i.e. a small (0.1 log unit) photochromatic interval in the longwave and a large (0.5 log unit) photochromatic interval in the middle and shortwave region of the spectrum relative to the achromatic threshold sensitivity. The spectral luminosity function obtained, using the VECP threshold amplitude criterion as index, was different from that using sensory criteria and exhibited an increased sensitivity near 600 nm and a loss in the green part of the spectrum.