In a finding that may someday offer help for those suffering from jet lag, researchers have found that the color of light -- for example, subtle differences in hues at dawn or dusk -- influence how our brains measure the time of day.
In animal studies, they found color's impact on the brain's internal "clock" can have an effect on physiology and that animals will adjust their behavior accordingly.
While light intensity, known as irradiance, changes with the rising and setting of the sun, there are also slight differences in the character of the light's color, with light at twilight hours being bluer than during daylight hours, researchers at the University of Manchester report in the journal PLOS Biology.
It may be color, as much as the intensity of light, that lets our brains know what time of day or night it is, they suggest.
In lab experiments, mice where exposed to different visual stimuli while the researchers recorded the electrical activity in the area of their brains that serves as the biological clock.
A significant portion of neurons in that region proved more sensitive to alterations of color -- particularly between yellow and blue -- than to changes in intensity, they found.
In further experiments using artificial light in which only the intensity, not the color, was cycled, the mice -- normally nocturnal animals who would become active only after dusk -- became active well before then, suggesting their body clocks weren't properly matched to the day-night cycle, the researchers reported.
"This is the first time that we've been able to test the theory that color affects our body clock in any mammal," says Timothy Brown of the university's Faculty of Life Sciences.
"What's exciting about our research is that the same findings can be applied to humans," he says, noting the study has revealed a new sensory mechanism for estimating time of day likely found in all mammals capable of color vision.
That suggests manipulating light and its color could fool our brains and thus our body clocks and could possibly help mitigate the effects of jet lag, they said.
"So, in theory, color could be used to manipulate our clock, which could be useful for shift workers or travellers wanting to minimize jet lag," Brown says.
