First, some circadian basics: Every time we see light—the natural daylight of the sun, the warm hue of a light bulb—it either reinforces or disrupts our inner clock. “Light-dark patterns are the single most important cue for our clocks,” explains Brant P. Hasler, Ph.D., a faculty member at the University of Pittsburgh Center for Sleep and Circadian Science. “Nothing else even approaches it.”
Ideally, the schedule of your internal clock will sync up with your external clock and you’ll be exposed to stimulating sun during the day and calming darkness at night. Of course, this isn’t always possible—especially if you’re working night shifts, studying long hours at school1, or traveling across time zones. “Circadian misalignment also occurs when an individual’s chronotype is at odds with their environment, e.g., when someone who is an ‘owl’ and prefers to be active in the evening is forced to be at work early in the morning,” adds Sofia Axelrod, Ph.D., a circadian clock researcher.
Misalignment between your light exposure and your body clock can have a negative impact on your sleep2, blood sugar management3, cardiovascular system4, and even skin health5. Well-timed light, on the other hand, has been shown to improve mood6 and overall life satisfaction7 (though it’s not always clear whether these benefits are the result of the circadian system or a direct effect of the light itself).
In the last few years, Axelrod has seen this circadian research begin to impact our medical system. For starters, it’s caused more sleep doctors to recommend keeping a dark bedroom in order to improve sleep quality—and reduce your risk of obesity, diabetes, and high blood pressure8 too. (One study published in PNAS found that just one night of moderate light exposure was enough to increase heart rate and next-morning insulin resistance9 compared to a night of dim light exposure in healthy adults.)
It’s also caused people to be more selective about their cellphone use, at least in the hours before bed, since the artificial blue light from our phones is stimulating and can be detrimental to sleep10.
More recently, the conversation around daytime light exposure has also picked up on social media. (Just look to the #circadian hashtag on TikTok—a compilation of videos of people getting out in the sunshine for the sake of their sleep and mood that has amassed 680.8K views.)
“Morning light is probably the most important for most people in order to keep their clocks on track,” says Hasler, since the average time it takes our internal clocks to go through a full cycle is 24.2 hours (cycles can range from less than 24 hours to over 25 hours). This means that we need to essentially turn our clocks back by 12 minutes each day, which morning sun exposure can help with. Evening light works against this.
As licensed clinical psychologist Aric Prather, Ph.D., explained on his episode of the mindbodygreen podcast, it can also be beneficial to “bundle” your morning sun with other healthy practices like walking and having social interactions.
However, Hasler caveats, “While morning light seems particularly important, it’s not like the light the rest of the day is not important” since natural sun exposure throughout the day seems to have a positive impact on our sleep and mental alertness.
Clearly, optimum light is something we should always be striving for, but the demands of modern life don’t make it easy. That’s where making small adjustments in the place you do have control over—your home—can have a bright impact. “I see a huge untapped potential in the application of circadian rhythms research in our lives,” says Axelrod.