Health experts have known for some time that exposure to light helps to regulate the body's internal clock. That's why humans get sleepy when it's dark outside and start to wake when it's light out. But new research has found that it may be more than light affecting our circadian rhythms; it may be the color of that light that really makes a difference.

For the study, researchers from the University of California, Santa Cruz took a look at how mice were affected by the color of the light they were exposed to. Specially, researchers wanted to know if the color of light affected the suprachiasmatic nucleus — the part of the brain that helps vertebrates regulate time using electrical and chemical signals.

To test this, researchers exposed mice to various colors and intensities of light while measuring nerve signals in the suprachiasmatic. Using an artificial sky, the mice were tested at various intensities of light, from bright light to complete darkness. And they were also tested when they were exposed to colors of light, such as the pinks and oranges that one might see during sunrise and sunset.

Researchers found that when the mice were exposed to light, as well as the various colors of light, they behaved perfectly normally. But when they were exposed to light that went from bright to dark without the color cues, their suprachiasmatic nerve signals lagged behind by about 30 minutes. Other physiological changes — such as a drop in body temperature — that might indicate the mice were ready to sleep also lagged behind by 30 minutes without exposure to colors.

So what does all of this mean for humans? It's possible that it doesn't mean a thing. But other sleep studies that have looked into changes within the suprachiasmatic have noted a strong correlation between reactions in mice and those in humans. And it also confirms the findings of another recent study that found that when young people (under aged 20) wore orange-tinted glasses at night while looking at the screens, they felt more sleepy than those that wore nothing or their regular, clear-lensed glasses.

And if humans are affected by the color — and not just the intensity — of light, it may help health experts create better treatment options from those who suffer from sleep disorders, even minor ones such as jet lag. 

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