Mesopic vision characteristics at decreased contrast in fog

Perception of different color contrast stimuli was studied in the presence of light scattering in a fog chamber in Clermont-Ferrand and in laboratory conditions where light scattering of similar levels was obtained. Blue (shortest wavelength) light is scattered in fog to the greatest extent, causing deterioration of vision quality especially for the monochromatic blue stimuli. We have done spectral measurements of the light source in different density fog conditions and no spectral changes were found produced by the fog. Psychophysical measurements of the acuity in fog were done for two subjects with optotypes analyzed for red and blue stimuli.