A waxing crescent moon is seen behind a streetlight with a newly installed LED fixture in 2011 in Las Vegas. The city was replacing 6,600 existing lights with the energy-efficient LEDs. It has since replaced tens of thousands more. Ethan Miller/Getty Images hide caption

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Age takes a toll on our internal clocks. Universal Stopping Point Photography/Getty Images hide caption

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As Aging Brain's Internal Clock Fades, A New Timekeeper May Kick In

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Gulping down coffee to stay awake at night delays the body's natural surge of the sleep hormone melatonin. Hayato D./Flickr hide caption

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Caffeine At Night Resets Your Inner Clock

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All in the name of science: Volunteers hike in Colorado during their one-week hiatus from electrical lighting. Courtesy of Kenneth Wright hide caption

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Don't Blame Your Lousy Night's Sleep On The Moon — Yet

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