JOHNSEN, S.*; KELBER, A.; WARRANT, E.J.; SWEENEY, A.M.; WIDDER, E.A.; LEE, R.L.; HERNANDEZ-ANDRES, J.; Duke University; Lund University; Lund University; Duke University; Harbor Branch Oceanographic Institution; U.S. Naval Academy; University of Granada: The color of night: twilight and nocturnal illumination and its effects on color perception

Recent studies have shown that some nocturnal insect and vertebrate species have true color vision, even under starlight. Given this, their vision would be affected by changes in the spectral quality of twilight and nocturnal illumination, due to the presence or absence of the moon, artificial light pollution and other factors. We investigated this in the following manner. First we measured the spectral irradiance (from 300 to 700 nm) during the day, sunset, twilight, full moon, new moon, and in the presence of high levels of light pollution caused by high pressure sodium lamps. The spectra were then converted to both human-based chromaticities and to relative quantum catches for the nocturnal hawkmoth Deilephlia elpenor , which has color vision. The reflectance spectra of various flowers and leaves and the red hindwings of D. elpenor were also converted to chromaticities and relative quantum catches. Finally, the achromatic and chromatic contrasts (with and without von Kries color constancy) of the flowers and hindwings against the leaves were determined under the various lighting environments. The twilight and nocturnal illuminants were substantially different from each other, resulting in significantly different contrasts. The addition of von Kries color constancy significantly reduced the effect of changing illuminants on chromatic contrast, suggesting that, even in this light-limited environment, the ability of color vision to provide reliable signals under changing illuminants may offset the concurrent 3-fold decrease in sensitivity. Given this, color vision may be more common in crepuscular and nocturnal species than previously considered.