Does the color temperature of nighttime light affect mouse activity?

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The spectral properties of light are important both for laboratory studies of circadian rhythms and for understanding artificial light at night in the field. Yet the trade-offs between light intensity and spectrum in masking behaviors remain largely unknown, even in well-studied organisms.

Researchers used a custom LED illumination system to expose wild-type house mice (Mus musculus) at night for one hour. They tested every combination of four intensities (0.01, 0.5, 5 and 50 lx) and three correlated color temperatures (CCTs: 1750, 1950 and 3000 K).

At 50 lx, light substantially suppressed cage activity, with consistently greater suppression at the higher CCT: 91% at 3000 K versus 53% at 1750 K. At the lowest intensity, 0.01 lx, mean activity increased most at the lowest CCT: by 12.3% at 1750 K versus 3% at 3000 K. Multiple linear regression confirmed that both CCT and intensity influenced activity changes; the scaled effect size of intensity was 3.6 times that of CCT. Activity suppression was significantly lower in male than in female mice.

At 50 lx, an assessment of light-evoked cFos expression in the suprachiasmatic nucleus found no significant difference between high- and low-CCT exposure. The researchers concluded that the significant differences by spectral composition show the need to account for light spectrum in circadian studies of behavior. They also concluded that spectral controls can mitigate some, but certainly not all, effects of light pollution on species in the wild.