Our Biological Clock Depends on the Color of Light and Not its Brightness

Our biological clocks may not be impacted by the time of day, but instead may be affected by the color of light that we experience. Scientists have found that there is a neuronal mechanism for how our internal clock can measure changes in light color that accompany dawn and dusk.

The researchers examined the change of light around dawn and dusk in order to analyze whether color could be used to determine the time of day. Well-known changes in light intensity occur as the sun rises and sets, but there are also changes in color. For example, twilight light is bluer than during the day.

After measuring the light, the scientists then recorded electrical activity from the "brain clock" of mice that were shown different visual stimuli. In the end, they found that many of the neurons were more sensitive in changes of color between blue and yellow than to changes in brightness.

The researchers then simulated an artificial sky that recreated the daily changes in color and brightness. When mice were placed under this artificial sky, the highest body temperatures occurred just after dusk, when the sky turned a darker blue. If only the brightness of the sky changed, though, the mice became more active before dusk, which meant that their body clock wasn't properly aligned to the day-night cycle.

"This is the first time that we've been able to test the theory that color affects our body clock in any mammal," said Timothy Brown, one of the researchers, in a news release. "It has always been very hard to separate the change in color to the change in brightness but using new experimental tools and a psychophysics approach we were successful.

The findings are published in the journal PLOS Biology.

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