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The Role of Light Color, Not Brightness, in Circadian Clock Entrainment

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Research by scientists at The University of Manchester has revealed that the color of light has a major impact on how our body clock measures the time of day.

The study tested the impact of color specifically and demonstrates that color provides a more reliable way of telling the time than measuring brightness.

In research published on April 17 in journal PLOS Biology, the researchers looked at the change in light around dawn and dusk to analyze whether color could be used to determine time of day. Besides the well-known changes in light intensity that occur as the sun rises and sets they found that during twilight, light is reliably bluer than during the day.

The scientists next recorded electrical activity from the body clock while mice were shown different visual stimuli. They found that many of the cells there were more sensitive to changes in color between blue and yellow than to changes in brightness.

The scientists then used measurements of the changes in the color spectra taken from the top of the University’s Pariser Building, to construct an artificial sky which recreated the daily changes in color and brightness.

Mice were placed beneath the sky for several days and their body temperature was recorded. As expected for nocturnal creatures, the highest body temperatures occurred just after night fell when the sky turned a darker blue—indicating that their body clock was working optimally.

When just the brightness of the sky was changed, with no change in the color, the mice became more active before dusk, demonstrating that their body clock wasn’t properly aligned to the day-night cycle.

Dr Timothy Brown from the Faculty of Life Sciences led the research. He says in a release: “This is the first time that we’ve been able to test the theory that color affects the body clock in mammals. 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.”

He continues: “What’s exciting about our research is that the same findings can be applied to humans. So in theory color could be used to manipulate our clock, which could be useful for shift workers or travelers wanting to minimize jet lag.”

Photography by David Gennard, The University of Manchester