PART 1: Sleep, Stress, and Your Body’s Clock

Written By Shari Dicks

Part 1 of 2

Sleep, stress, and mood feed each other. When you sleep badly, the next day feels harder, stress hits harder, and your mood drops. When you're stressed or low, your mind races at night and sleep doesn't come easily. Most sleep advice focuses on bedtime: a dark room, no screens, a calm routine. Those help. But a lot of what decides how you sleep, and how you feel, happens long before bed.

Your body runs on a daily rhythm. An internal clock decides when cortisol, your main stress hormone, rises to wake you up, when it falls so you can wind down, and when your body releases melatonin, the hormone that helps you fall asleep. When that rhythm is steady, it's easier to feel awake during the day and settle at night. When it's off, you can end up wired at bedtime and dragging in the morning.

The main thing that keeps that clock on time is light. The light you get in the morning, the light you get late in the day, and the lamps and screens in your evening all tell your body what time it is. That makes light one of the simplest tools we have for better sleep, a steadier stress response, and a steadier mood, and one most of us never think about.

Andrew Huberman explains this in his book Protocols, which I've been listening to. The research behind it is solid, and the light chapters are some of the most useful material I've come across on sleep. He comes back to light again and again, in the sleep protocols and again in the light protocols, because it matters that much. The message gets through.

I also rolled my eyes a lot. Not because the science is wrong, but because so much of it feels like it was written by somebody who is living by themselves and sets their own schedule. Get outside within an hour of waking. Turn off the overhead lights at night. Keep screens out of the evening. It's protocol after protocol, and reading them can make you want to throw your hands in the air and laugh.

My life right now: I'm in perimenopause. I have two teenagers with late schedules and a school day that can start at 6 a.m. I have a dog and cats who need to be fed and walked. I share a bed with my husband. Some nights I'm not home from driving kids around until 9:45. My time is not my own, and I know a lot of women reading this can say the same.

Perimenopause also makes sleep more fragile, and it's made me realize how much I need to prioritize it. And I've struggled with chronic depression for as long as I can remember. I definitely struggle with seasonal affective disorder, and January is notoriously brutal for me. That's a big part of why light matters to me. It isn't only a sleep tool. Intentional light exposure has real research behind it as a therapy for depression and seasonal affective disorder. All of that makes the parts I can control matter more, not less.

So this post does two things. It explains, in plain language, how your daily rhythm shapes your sleep, your stress, and your mood, and how light keeps that rhythm on time. Then it offers the realistic version of each piece, the one that fits into a real house with real people in it.

Cortisol is not the villain

For a long time, I only knew cortisol as a stress hormone and the thing that gave you belly fat. That's most of what the wellness world tells us about it, and it leaves out the most important part.

Cortisol is not good or bad. It rises and falls on a daily rhythm. It's meant to be high in the morning, when it helps you wake up, feel alert, and get moving. It's meant to drift lower through the day and be at its lowest at night, so your body can rest. Timing is what matters.

That timing is why cortisol matters for sleep. When it rises and falls on schedule, you have energy when you need it and your body can let go at night. When the rhythm gets thrown off, you can feel flat in the morning and keyed up when you're trying to fall asleep.

The biggest rise happens right after you wake up. Researchers call it the cortisol awakening response: a sharp climb in cortisol over the first 30 to 60 minutes of your day. That morning surge is healthy. It's your body getting ready for the day.

Light makes that morning rise stronger. In a study published in 1999, people who sat in bright light for an hour after waking had about 35% more cortisol than people who stayed in dim light. The same light in the evening had no effect on cortisol. The timing changed everything.

Cortisol also helps us handle stress, and Huberman makes a point I find really valuable: the goal isn't only to manage stress. It's to build our capacity for it. Researchers call this hormesis. Short challenges followed by recovery, like a good workout, can make the body more resilient over time. The recovery part matters as much as the challenge, and sleep is a big part of recovery. That's different from stress that never lets up, and if you're already carrying a lot, adding more isn't the answer. Cortisol is something to work with, not something to fight.

What keeps cortisol on its rhythm is a clock, and light is what sets it.

Your clock: the SCN, explained simply

Deep in your brain is a tiny cluster of cells called the suprachiasmatic nucleus, or SCN. It's your master clock. It sets the timing for your whole body: when cortisol rises, when melatonin comes in at night, when your body temperature rises and falls, and when you feel alert or sleepy.

Your clock isn't perfect on its own. Left alone, it runs a little longer than 24 hours, about 24 hours and 11 minutes on average. So every day it needs a signal from the outside world to line back up with the real day. Its main signal is light.

Your eyes have special cells whose job isn't to help you see. Their job is to measure how bright it is and report that to your clock. These cells contain a light-sensitive pigment called melanopsin. They respond most to the blue-ish light that's plentiful in daylight, and they need a lot of light to respond fully, far more than ordinary indoor lighting gives them. That's a big reason outdoor light matters so much.

When those cells pick up bright light in the morning, the message is: the day has started. The clock sets itself from that signal, and it schedules the rest of your day from there, including when melatonin comes in that night.

It helps to know what melatonin actually does. It isn't a sleeping pill your body makes. It's more like a signal that says it's nighttime, which opens the door to sleep. The earlier and more clearly your clock gets its morning signal, the more on time that nighttime signal tends to be.

Timing works in both directions. Light in the morning pulls your clock earlier. Bright light late at night pushes it later. That's why the same bright light can help you at 7 a.m. and work against you at 11 p.m.

This was the part that clicked for me. Morning light doesn't help you sleep because of the cortisol boost on its own. It helps because it sets your clock, and your clock schedules both the morning cortisol rise and the evening melatonin. Light in the morning is really an investment in your night.

The "first hour" advice is a target, not a deadline. Light earlier in the morning has a stronger effect, and getting it at roughly the same time each day helps your clock stay steady. But light at 90 minutes still counts. Light at two hours still counts. If you miss the first hour, you haven't missed your chance.

One more thing that matters for women: a 2024 study found that women's bodies responded more strongly than men's to bright light, though not to dim or moderate light. Bright light could be an especially strong lever for us, in the morning and at night.

Light as a therapy for depression and SAD

The same clock that times your sleep is tied to your mood. When the days get shorter in fall and winter, less light reaches it, and for a lot of people, mood drops with the light.

Seasonal affective disorder, often called SAD, is a form of depression that comes on in the fall or winter and usually lifts in the spring. If the dark months are hard for you too, you're not imagining it.

This is where intentional light exposure stops being a wellness tip and becomes a real treatment. Light therapy uses a light box, a lamp made to be much brighter than ordinary indoor lighting. Brightness is measured in lux. Most of the research uses a 10,000 lux light box for about 30 minutes, soon after waking.

For seasonal depression, light therapy is a first-line treatment. It has been tested in more than 70 controlled studies, and clinical guidelines recommend it as a first choice. In one 2006 trial, people with winter depression got either 30 minutes of 10,000 lux light each morning or a common antidepressant, fluoxetine (Prozac). The two worked about equally well. About half of each group reached remission, meaning their symptoms largely went away. The light worked a little faster and caused fewer side effects.

Morning matters. Light therapy seems to work partly by moving the body clock earlier, which is exactly what morning light does. When researchers compared times of day for winter depression, morning light worked better than evening light. In one study, about 60% of people improved markedly with morning light, compared with about 30% with evening light.

It helps beyond winter, too. In a 2016 trial of people with depression that wasn't seasonal, 30 minutes of 10,000 lux light each morning worked better than a placebo, both on its own and combined with an antidepressant. The combination worked best. A 2024 review in JAMA Psychiatry pulled together 11 clinical trials with more than 850 people with nonseasonal depression. When bright light therapy was added to their treatment, about 41% reached remission, compared with about 24% of people who didn't get it.

Bipolar disorder is different. For people with bipolar disorder, bright morning light can tip mood too far the other way, into mania or a mixed state. Researchers have found that light at midday, used under a doctor's care, can help bipolar depression. In a 2018 trial, about 68% of people who got midday bright light reached remission, compared with about 22% who got a placebo light. For bipolar disorder, light therapy should only happen with a doctor guiding it.

Light therapy is a real treatment, so it deserves real guidance. It's used alongside other care, not instead of it. If you live with depression or SAD, light is worth bringing up with your doctor or therapist. You can ask whether light therapy makes sense for you, what kind of light box to use, how long to use it, and what time of day.

Morning light, the realistic version

Morning light is the strongest signal you can give your clock, for sleep and for mood, so it's the best place to start.

The ideal version is to get outside within an hour of waking and let daylight reach your eyes.

How long? Huberman's general guide is about 5 to 10 minutes on a clear morning, 10 to 20 minutes when it's cloudy, and 20 to 30 minutes when it's heavily overcast. These are estimates, not exact cutoffs, but they're a helpful place to start.

Cloudy days still count. Huberman makes this point by comparing a cloudy morning to midnight. Even a gray, overcast day is enormously brighter than the night, and your clock can tell the difference. To put numbers on it: indoor lighting is usually a few hundred lux. Daylight outside, even on a cloudy day, is usually thousands of lux. A bright, sunny day can reach 100,000 lux. At night, even under a full moon, it's less than 1 lux. On cloudy days you just need a little longer.

Why outside instead of behind a window? Light through a window is much weaker by the time it reaches your eyes. Huberman estimates it's about 50 times less effective than being outside. Researchers who measure daylight indoors say the bigger loss isn't the glass itself. It's being inside: how far you are from the window, how big it is, and which way you're facing. A bright spot right next to a big window is better than nothing. Stepping outside is far better. The same goes for a car windshield.

Protect your eyes. Never look directly at the sun. You don't need to. Just being outside with your eyes open to the daylight is enough. Blinking and squinting are normal, so don't fight them. Huberman suggests skipping sunglasses for these few minutes if it's safe and comfortable for you. Regular glasses and contact lenses are fine.

In summer, the ideal works for me. I take the dog out first thing, and the sun is already up. In fall and winter, my mornings don't match it. It's pitch black when I go out with the dog. By the time the sun comes up, I've fed the animals, made sure whoever needs to be up is up and fed, and I'm driving to school.

That's why I bought a 10,000 lux light, the same kind of light box used in the research. It brings some of the brightness of being outside into your house, close to your face, where those light-measuring cells in your eyes can pick it up.

Getting outside within an hour can feel impossible, sometimes because the sun isn't up and sometimes because I have 5,000 things to do. Having a 10,000 lux light in my bathroom while I wash my face, or in the kitchen while I feed the animals and make my coffee, feels much more doable. I'm putting it where I already am.

I also think there's real value in feeling like I'm doing something good for my body, even before I know how well it works. Psychosomatic things are still real. They're still helpful.

If you're thinking about a light box, a few things to know:

  • Check the distance. A 10,000 lux rating only applies at a certain distance from the light, often about 12 to 24 inches. The farther away you are, the less light you get.

  • Plan on about 30 minutes. That's what most of the research uses, in the morning, soon after waking.

  • Look for UV filtering. You want bright light, not ultraviolet light.

  • Place it off to the side. It should be in your field of view, slightly above eye level, not something you stare directly into.

  • Talk to your doctor first if you have any eye conditions, take medication that makes you more sensitive to light, or have bipolar disorder.

And the free versions count:

  • A morning walk, even a short one. I try to fit in a walk with the dog after school drop-off.

  • The drive to school or work with the window rolled down.

  • Coffee or breakfast on the porch or front step, or with the door open.

  • Stepping outside for a few minutes once the sun is up, even if it's later than the first hour.

Your morning coffee

Coffee is part of how most of us manage our energy, so it's worth knowing what its timing does to your sleep.

I delay my morning coffee a bit. I usually have it after the school run. Huberman suggests waiting 90 to 120 minutes after waking, so I looked at the research.

The reasoning behind it doesn't hold up well. The idea is that waiting lets your body clear a sleep chemical called adenosine and avoids an afternoon crash. Adenosine builds up the longer you're awake, and it's part of what makes you feel sleepy by the end of the day. Caffeine works by blocking it. But a 2024 review of caffeine research found no real evidence that delaying coffee prevents an afternoon crash. The adenosine changes after waking happen within minutes, not over hours. And for people who drink coffee every day, caffeine's effect on cortisol becomes much smaller.

So if you like waiting and it feels good, keep doing it. If you need your coffee right away, the research doesn't give you a reason to worry.

The timing that does matter is later in the day. In one study, the caffeine in about a double espresso, taken three hours before bed, pushed people's internal clocks about 40 minutes later. In another, a large dose of caffeine, about what's in two to three cups of coffee, taken six hours before bed still cut sleep by more than an hour. Your afternoon coffee affects your night more than your morning coffee does. If sleep is hard for you, moving your last cup earlier in the day is an easy thing to try.

Sunset and the evening wind-down

Evening is when your body is supposed to start winding down: cortisol at its lowest, melatonin starting to rise. The light you get in the evening can either support that or work against it.

The sunset signal. As the sun gets low in the late afternoon and evening, its light shifts. It gets warmer, with more of the red and orange end of the spectrum. Huberman explains that viewing that light around sunset tells your clock that evening is coming, and that it can help protect you from the effects of the artificial light you get later at night.

The research on this is still growing. In a 2019 study of young women, those who got bright light in the early evening were less affected by the room light they were exposed to later that night. Your clock also seems to keep a memory of the light you've had in the days before. In another study, a week of bright days made people's melatonin less sensitive to light at night. Studies in mice have found that the brain's clock tracks the changing colors of dawn and dusk, not just how bright it is. Whether that works the same way in people is still being studied. The practical version is the same either way: if you can, step outside for a few minutes in the late afternoon or around sunset. As with the morning, there's no need to look at the sun.

Why evening light matters so much. In one study, ordinary room light in the hours before bed delayed the release of melatonin in 99% of the people studied. It also shortened the amount of time their bodies were releasing melatonin by about 90 minutes. That wasn't bright light. That was regular household lighting.

Short and long wavelengths, in plain terms: light comes in different colors, and color is measured in wavelengths. Short-wavelength light is on the blue end. It's strong in daylight, phone and computer screens, white LED bulbs, and most overhead lighting. Those melanopsin cells in your eyes are most sensitive to it, so your clock reads blue-heavy light as daytime. Long-wavelength light is on the red and amber end, like firelight or candlelight. Your clock is much less sensitive to it, so it reads as night.

Brightness matters as much as color. Dim light of any color is gentler than bright light.

A note on "warm white" or "soft white" bulbs: they look orange-ish, but most of them still contain blue light, because of how white LEDs are made. They're better than bright overhead lights, but they're not the same as true amber or red light.

Blue light blocking glasses. Huberman recommends wearing glasses that block short-wavelength light in the evening, and he specifically recommends Roka's red-lens glasses. It's worth knowing that he has been a scientific advisor to Roka and that Roka has sponsored his podcast.

The research on these glasses is mixed. A 2023 Cochrane review, which pulls together all the available trials, found the evidence on sleep too uncertain to say much either way. The clear or lightly tinted "blue light" lenses sold for screen use don't block much. Deeply tinted amber, orange, or red lenses block far more, and they have some support in small trials, especially for people with insomnia. One 2018 study found that people with insomnia slept better when they wore amber lenses for two hours before bed.

If you want to try them, look for deeply tinted amber, orange, or red lenses and wear them for the couple of hours before bed. They don't have to be expensive. And don't wear them during the day, when you want all the daylight you can get.

My realistic version: I can't turn off every light in a house with three other people in it. What I can control is my own space. I keep the lights off in my room. I ordered red nightlights that turn on when the lights go off, so I can wash my face and do my whole bathroom routine without the bright overheads. I'd rather use lamps than overhead lights in the evening when I can. Dimmer, warmer light at night also just feels calmer, and that matters when you're trying to settle.

Screens are harder. Some nights, I need to check an email to find out what time someone has to be at school the next morning, set alarms, and check that homework got done. So I try to keep it short, turn the brightness down, and do what I can.

The middle of the night

Light in the middle of the night can shift your clock more than light at almost any other time, and it's also when the right light matters most for safety.

Why it matters for your clock. Huberman talks about the temperature minimum: the point in the night when your body temperature is at its lowest, usually about two hours before you normally wake up. Bright light in the hours before that point pushes your clock later. Light after it pulls your clock earlier, which is part of why morning light works. A 2 a.m. bathroom trip usually lands before your temperature minimum, so flipping on a bright overhead light then is sending your clock the wrong message at the worst time. Melatonin also peaks in the middle of the night, usually between about 2 and 4 a.m., and bright light tells your body to stop making it, which can make it harder to fall back asleep.

Why it matters for safety. Getting up to use the bathroom at night gets more common in midlife, and with age it becomes a real safety issue. Waking up at night to urinate is a well-known risk factor for falls in older adults, and falls are the leading cause of injury deaths in adults over 65. One study found that balance and walking are measurably worse right after waking in the middle of the night, even in healthy adults in their 60s.

So the answer isn't stumbling to the bathroom in the dark. That same study found that bright room light didn't improve balance any more than dim orange light did. You don't need bright light to get there safely. You need enough light to see where you're going.

The realistic version: a dim red or amber nightlight, placed low, along the path from your bed to the bathroom and in the bathroom itself. Motion-activated ones turn on by themselves, so you never have to search for a switch. They light the way without telling your clock it's morning. Getting up slowly helps too. This is exactly why I use red nightlights, and if you have an older parent or anyone in your life who gets up at night, it's one of the simplest safety upgrades you can make.

Screens and teenagers

Teenagers are caught in the same loop of sleep, stress, and mood as the rest of us, and their schedules make it worse. When teens don't get enough sleep, it shows up in their mood, their focus, and their schoolwork.

Every parent of a teenager also knows this part: our kids are pretty sure we're the dumbest people in the world. I say that with laughter, in hopes of connecting. And still, I want to give them what I've learned, because it would only make them feel better. The question is how.

Start with their biology. During puberty, the body clock shifts later, by up to two hours. A teenager who isn't tired at 10 p.m. isn't being difficult. Their clock has actually moved.

This is where the system works against them. The American Academy of Pediatrics and the American Academy of Sleep Medicine both recommend that middle and high schools start at 8:30 a.m. or later. Many don't. A school day that starts at 6 a.m. is running directly against teenage biology. That isn't a teenager problem. It's a scheduling problem.

Their social lives really do live on their phones. Snapchat, TikTok, YouTube: that's where their friends are, and those apps are designed to be hard to put down. Asking a teenager to give that up at night is asking them to step out of their social world. It makes sense that they push back.

I have a very vivid memory of being a teenager in my bedroom, upset about feeling dismissed and unheard. I made a promise to myself, at 15, that I would never forget how I felt. It was almost a promise to my future kids: that I would remember they are people too, capable of feeling unheard, and that I would take them seriously. Every older generation feels a disconnect with the younger one. I want to acknowledge that, not pretend it isn't there.

So invitation works better than instruction. Some ideas worth trying:

  • Explain their biology. Teenagers respond to information more than rules. Knowing why their body works the way it does can make the choice feel like theirs.

  • Go first. Make it a household change, not a rule for kids. If parents' phones charge in the kitchen overnight too, it's a family habit instead of a punishment.

  • Talk about what they care about. Sleep and light affect energy, mood, skin, focus, and sports performance. Those are better reasons for a teenager than "because I said so."

  • Shrink the ask. Brightness down and night mode on in the evening. Notifications silenced after a set time, with a few chosen people still allowed through. Phone charging across the room instead of in bed. Small changes are easier to say yes to.

  • Win the morning instead of fighting the night. Morning light pulls their clock earlier, which makes it easier to fall asleep at night. Windows rolled down on the drive to school, a few minutes outside before they leave, a bright light in the bathroom while they get ready. Morning light causes a lot less conflict than taking away a phone at 10 p.m.

  • Ask what they notice. "How did you feel today?" goes further than "I told you so."

One thing at a time

Better sleep, a steadier stress response, and a steadier mood don't require a perfect protocol. So much of this comes down to coming back to natural rhythms: bright light in the morning, dimness at night, the way our bodies have always worked. These choices are within our grasp. I also know how overwhelming it can feel. There's always a list of things we're supposed to be doing: eating enough protein, prioritizing sleep, getting social connection, taking care of our mental health, exercising every day. There isn't enough time in the day, and it can make you want to throw your hands up.

So pick one thing. What feels easy? What feels accessible? Start with that, and build from there.

A few places to start, if you want them:

  • A few minutes outside in the morning, whenever you can get them, cloudy days included.

  • A 10,000 lux light where you already are in the morning, if getting outside isn't possible.

  • A conversation with your doctor or therapist about light therapy, if you live with depression or SAD.

  • A few minutes outside in the late afternoon or around sunset.

  • Your last coffee a little earlier in the day.

  • Lamps instead of overheads after dinner.

  • Amber, orange, or red glasses for the couple of hours before bed.

  • A dim red or amber nightlight along the path to the bathroom, ideally motion-activated.

For me, right now, it's a 10,000 lux light in my bathroom for the mornings, and red nightlights for the evenings and middle-of-the-night bathroom trips.

Light is one piece of the story. Some nights, even when you do everything you can, sleep still doesn't come, and your mind won't stop. Part 2 is about those nights: what actually helps your nervous system settle, and why rest still counts even when sleep doesn't come.

Shari Dicks, Sixth House Healing

Sources

Cortisol, stress, and the body clock

Light as a therapy for depression and SAD

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  • Terman M et al. A controlled trial of timed bright light and negative air ionization for treatment of winter depression. Archives of General Psychiatry, 1998. https://pubmed.ncbi.nlm.nih.gov/9783557/

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  • Lam RW et al. Efficacy of bright light treatment, fluoxetine, and the combination in patients with nonseasonal major depressive disorder: a randomized clinical trial. JAMA Psychiatry, 2016.

  • Menegaz de Almeida A et al. Bright light therapy for nonseasonal depressive disorders: a systematic review and meta-analysis. JAMA Psychiatry, 2024. https://jamanetwork.com/journals/jamapsychiatry/article-abstract/2824482

  • Sit DK et al. Adjunctive bright light therapy for bipolar depression: a randomized double-blind placebo-controlled trial. American Journal of Psychiatry, 2018.

Morning light

Coffee

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Evening light, sunset, and glasses

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  • Walmsley L et al. Colour as a signal for entraining the mammalian circadian clock. PLOS Biology, 2015.

  • Mouland JW et al. Cones support alignment to an inconsistent world by suppressing mouse circadian responses to the blue colors associated with twilight. Current Biology, 2019. https://pmc.ncbi.nlm.nih.gov/articles/PMC6926481/

  • Gooley JJ et al. Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans. Journal of Clinical Endocrinology & Metabolism, 2011. https://pmc.ncbi.nlm.nih.gov/articles/PMC3047226/

  • Singh S et al. Blue-light filtering spectacle lenses for visual performance, sleep, and macular health in adults. Cochrane Database of Systematic Reviews, 2023. https://www.cochrane.org/evidence/CD013244

  • Shechter A et al. Blocking nocturnal blue light for insomnia: a randomized controlled trial. Journal of Psychiatric Research, 2018.

  • Roka, Our Story (Huberman as scientific advisor). https://uk.roka.com/pages/why-roka

The middle of the night

Teenagers

Shari Dicks
Next

PART 2: When Sleep Doesn't Come