If you know anything about the circadian rhythm, it’s probably that keeping it dialed is really important for a good night’s sleep. (If you don’t know anything about the circadian rhythm, it’s the body’s internal 24-hour clock—it’s what makes you feel sleepy or awake.) The secret to keeping that system humming is managing light exposure.

“Light is the primary cue to the circadian system,” Lynne Peeples, science journalist and author of The Living Clock: Living in Sync with Our Circadian Rhythm, told the Daily Beast in an interview. “The system expects bright blue-rich light during the day, and it expects the night to be dark—aside from maybe a flicker of warm firelight, moonlight, or the equivalent.”

The light’s color is key, because our bodies are wired to see blue light as a daytime cu

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