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How Body Clocks Tell Time Using Color
When the sun rises, your body clock nudges you awake. And when the sun sets, you may catch yourself yawning.

While we have long thought that it was the brightness of the light that did this, British researchers have determined it is the color of the light--not its intensity--that ignites our body clock to measure the time of day.

Led by Dr. Timothy Brown of the University of Manchester, the team carefully studied the change in light at dawn and dusk. They found that in addition to the well-known changes in light intensity that occur as the sun rises and sets, the light is reliably bluer then than during the day.

Find out why your body clock is to play for your late-night snack attack.

Study No. 1: Using mice, the scientists recorded electrical activity from the rodents' body clocks while they were shown different visual stimuli. They discovered that many of the cells were more sensitive to changes in color between blue and yellow than to changes in brightness.

Study No. 2: Next, the British scientists used measurements of the changes in the color spectra taken from the top of one of the buildings at the University of Manchester to construct an artificial sky which recreated the daily changes in color and brightness. They placed mice beneath that artificial sky for several days and recorded their body temperatures. 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 only 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.

"This is the first time that we've been able to test the theory that color affects the body clock in mammals," said Brown. "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."

So what? Brown says the findings can be applied to humans, using color to manipulate our body clock, something that would be incredibly useful for shift workers or travelers wanting to minimize jet lag.

The study findings were published in the Open Access journal PLOS Biology.

Who is healthier...larks for night owls? They consume about the same amount of calories daily, yet one is heavier than the other.

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