Relative importance of intensity and spectrum of artificial light at night in disrupting behavior of a nocturnal rodent

The influence of light spectral properties on circadian rhythms is of
substantial interest to laboratory-based investigation of the circadian
system and to field-based understanding of the effects of artificial light
at night. The tradeoffs between intensity and spectrum regarding masking
behaviors are largely unknown, even for well-studied organisms. We used a
custom LED illumination system to document the response of wild type house
mice (Mus musculus) to 1-hr nocturnal exposure of all combinations of four
intensity levels (0.01, 0.5, 5, and 50 lx) and three correlated color
temperatures (CCT; 1750, 1950, and 3000 K). Higher intensities of light
(50 lx) suppressed cage activity substantially, and consistently more for
the higher CCT light (91% for 3000 K; 53% for 1750 K). At the lower
intensities (0.01 lx), mean activity was increased, with the greatest
increases for the lowest CCT (12.3% increase at 1750 K; 3% increase at
3000 K). Multiple linear regression confirmed the influence of both CCT
(p<0.001) and intensity (p<0.001) on changes in
activity (r2=0.66, F9,171=3.33; p<0.001) with the scaled effect
size of intensity 3.6 times greater than CCT. Activity suppression was
significantly lower for male than female mice (p<0.0001).
Assessment of light-evoked cFos expression in the suprachiasmatic nucleus
at 50 lx showed no significant difference between high and low CCT
exposure. The significant differences by spectral composition illustrate a
need to account for light spectrum in circadian studies of behavior and
confirm that spectral controls can mitigate some, but certainly not all,
of the effects of light pollution on species in the wild.