Morning, midday, and evening—what the sun does at each stage, and what happens when we get it wrong

The whole light situation landed on my radar through conversations about vitamin D3 supplementation. It’s one of the most commonly discussed supplements in the metabolic health space—long before I understood any of the deeper science, it was always something I heard people talking about for improving general health. Take your D3. Get your levels checked. Supplement through the winter.

At some point, I had to think to myself: we haven’t been able to supplement vitamin D for our entire existence as humans.

Where do we get it? We get it from the sun.

That question opened a door I wasn’t expecting. Once I started digging into what the difference is between supplementing vitamin D and getting it from actual sunlight, the picture got a lot bigger than a pill bottle. Vitamin D is more of a hormone than a vitamin—it’s synthesized through a process that begins when UVB radiation hits the skin, converts 7-dehydrocholesterol into previtamin D3, which then travels to the liver and kidneys for activation. There are many factors involved when getting vitamin D from sunlight out in nature that cannot be captured in a pill—the infrared light that primes the skin for UV exposure, the nitric oxide release that supports cardiovascular function, the beta-endorphin production that influences mood, the melatonin synthesis that occurs through a separate pathway in the skin itself.

That rabbit hole led me to something I think deserves more attention than it gets in the health and wellness space: the sun at different times of the day serves different purposes, and our bodies were built to receive all of them.

Morning light—setting the clock

Early morning sunlight—direct, outside, within the first hour or so of waking—does something no supplement can replicate. It anchors the cortisol awakening response and sets up appropriate melatonin release 12 to 14 hours later.

When light in the blue-dominant spectrum of early morning hits the intrinsically photosensitive retinal ganglion cells in your eyes, it sends a signal through the retinohypothalamic tract to the suprachiasmatic nucleus—the master circadian clock in the brain. That signal tells the body: it’s daytime. Cortisol rises appropriately (this is the one time of day you want it elevated), body temperature begins to climb, and the internal clock starts counting down toward the melatonin release window in the evening.

I don’t typically get a lot of pushback on whether or not this makes sense when I explain it to people. The logic clicks—of course the body uses light to set its clock; it’s been doing that for all of human existence. The challenge isn’t understanding; it’s the habits.

A lot of people have fallen into patterns of staying up late or being night owls, which usually means they’re also sleeping in. That’s hard to get away from—especially when someone has spent years in that rhythm and their social life, work schedule, or identity is built around it. What I’ve found, though, is that it doesn’t seem to take long to reset someone’s circadian clock once they commit to the morning light exposure. Getting over the hump by viewing morning sunlight for a couple of days in a row seems to pretty effectively shift when a person is getting tired in the evening and when they begin to naturally wake up in alignment with sunset and sunrise.

The key is consistency over duration. Ten to fifteen minutes of outdoor light exposure in the morning—not through a window, not while wearing sunglasses—is the threshold most research points to. On overcast days, you may need longer, as cloud cover reduces the light intensity reaching the retina; the exposure still counts, it just takes more time to deliver the same signal strength.

Midday light—the vitamin D window

The midday sun—roughly 10 AM to 2 PM depending on latitude and season—is when UVB radiation is strong enough to trigger the vitamin D synthesis process in the skin. This is the window most people think of when they hear “get some sun,” and it’s the window that matters most for vitamin D production.

How much exposure you need varies based on skin tone, latitude, time of year, and body surface area exposed. Someone with lighter skin at a lower latitude in summer may need only 10 to 15 minutes of midday sun exposure on uncovered arms and legs. Someone with darker skin, at a higher latitude, or during winter months may need substantially more—or may not be able to produce adequate vitamin D from sun exposure alone during certain seasons.

This is where supplementation enters the picture, and I think it’s important to frame it accurately. I don’t think D3 supplementation is a replacement for the sun—that’s why it’s considered a “supplement,” right? It fills a gap when the real thing isn’t accessible. In situations where someone genuinely can’t get adequate midday sun exposure—due to geography, work schedule, indoor lifestyle, or seasonal limitations—D3 supplementation serves as a necessary bridge. D3 paired with K2 is the combination I see most benefit from in practice; K2 helps direct calcium to bones and teeth rather than allowing it to accumulate in soft tissues and arteries.

The goal isn’t to choose between sunlight and supplementation; it’s to get as much of the real thing as your situation allows and supplement what you can’t cover. For some people, that means D3 year-round. For others, it means supplementing only during winter months when UVB availability drops below the threshold for skin synthesis. In either case, it comes down to doing the best you can until your situation changes with work or responsibilities—assuming you want to change those things. For a deeper dive on how all of this connects to fixing broken sleep, I’ve written a comprehensive guide.

Evening light—the wind-down signal

As the sun moves toward the horizon, its light shifts toward the red and amber end of the spectrum. The blue wavelengths that dominate morning and midday light are scattered by the atmosphere, and what reaches us is a warmer, dimmer signal that the body reads as the beginning of the wind-down.

This is when the suprachiasmatic nucleus begins transitioning toward melatonin production. Viewing the sunset—or at minimum, being exposed to the naturally dimming light of late afternoon and evening—reinforces the circadian signal that started with morning light exposure. The day has a beginning and an end, and the body is designed to register both.

For the majority of human existence, this is how it worked. When the sun went down, the light went away. The body shifted into recovery mode. Melatonin rose. Sleep architecture organized itself around the darkness.

The problem, obviously, is that we no longer live in that environment.

What artificial light disrupts

The modern environment is saturated with light that the body wasn’t built to process at the times we’re experiencing it. Overhead LEDs, screens, televisions, and ambient lighting all emit wavelengths—particularly in the blue spectrum—that the retinal ganglion cells interpret as “it’s still daytime.” The circadian signal that was supposed to trigger melatonin production gets delayed or suppressed entirely.

This isn’t a subtle effect. Research consistently shows that evening exposure to blue-dominant light delays melatonin onset by 90 minutes or more, reduces total melatonin production, and shifts the circadian phase later—essentially telling the body that evening is actually afternoon. Over time, this chronic circadian disruption has been associated with disrupted sleep architecture, impaired glucose metabolism, increased inflammatory markers, and hormonal signaling changes that compound the metabolic challenges many people are already carrying.

I try to keep things as simple as possible when explaining this to clients and patients. When it comes to the photoreceptor issue, I often tell people to compare two nights: a night of watching TV with blue-light-blocking glasses on, and a pre-planned night where after the sun goes down, no artificial lights are on and you just go to bed. It’s a little oversimplified, but people always notice a difference. That experiential data tends to land harder than any mechanism I could explain.

Blue-light glasses—helpful, but not the whole picture

This brings up a point that I think is worth its own section, because it’s a place where well-intentioned people often stop short.

Blue-light-blocking glasses have become popular, and for good reason—they reduce the amount of blue light reaching the retina, which helps preserve the melatonin signal in the evening. If you’re going to get a pair for use after dark, it would be ideal to get deep red lenses. The standard amber or yellow “blue-light” glasses filter some of the spectrum, but you generally don’t want to be able to perceive the color blue through the lenses. If you can tell something is blue while wearing them, then blue is making it into your eyes and the filtering is incomplete.

Here’s the part that gets less attention: it’s not just about your eyes.

Your skin is covered in photoreceptors. Opsins—the same class of light-sensitive proteins found in the retina—are expressed in skin cells throughout the body. Research has identified these photoreceptors in keratinocytes, melanocytes, and other skin cell types, where they respond to light wavelengths and influence local biological processes including melanin production and circadian gene expression.

What this means practically is that wearing glasses addresses the eyes, but it doesn’t address full-body light exposure. If you’re wearing your blue-light-blocking glasses while sitting in a brightly lit room in shorts and a t-shirt, your skin is still receiving the signal that it’s daytime. The glasses help—I’m not discounting them—but they’re one layer of a more complete approach.

That said, it’s also not just about the blue. The brightness of light matters independent of its spectral composition. A very bright amber-tinted room can still suppress melatonin production, just less efficiently than a blue-dominant one. Dimming lights in the evening—regardless of their color temperature—is a meaningful step. The goal is to give the body a light environment that approximates what it would have experienced for most of human history: bright during the day, dim to dark in the evening.

Practical light hygiene for modern life

I recognize that most people can’t restructure their lives around the solar cycle—and I’m not asking anyone to. Jobs have hours. Kids have schedules. Life happens indoors under artificial light whether we like it or not.

What I’ve seen work in practice is a layered approach that prioritizes the highest-impact changes first:

Morning sunlight exposure — Get outside within the first hour of waking. Ten to fifteen minutes, no sunglasses. This is the single highest-leverage circadian intervention and it costs nothing. On days when you can’t get outside—weather, schedule, location—a 10,000 lux light therapy lamp used for 20 to 30 minutes during the morning hours can partially replicate the signal; it’s not the same as natural light, but it’s meaningfully better than nothing.

Midday sun when possible — Even a short walk during lunch provides UVB exposure for vitamin D synthesis and reinforces the daytime circadian signal. The skin exposure matters; rolling up sleeves and ditching the sunglasses for this window helps.

Evening light reduction — Start dimming indoor lights as the sun goes down. Switch to warmer-toned bulbs (2700K or lower) in living spaces used after dark. Red or amber salt lamps, candles, or low-wattage warm bulbs create an environment that the body reads as transitional rather than full-daylight. Deep red blue-light-blocking glasses if screens are being used. Reducing screen brightness to the minimum comfortable level.

Bedroom environment — Complete darkness for sleep. Blackout curtains, covering LED standby lights on electronics, removing or covering any light source. The research on even small amounts of ambient light during sleep and its effects on glucose metabolism and cardiovascular markers is striking enough to be worth taking seriously.

Of course, there are situations in which this kind of sleep and wake pattern isn’t possible due to people’s jobs or responsibilities. Shift workers, parents of infants, people with irregular schedules—I try to take all of that into account. The principles stay the same; the application gets creative. For someone working nights, strategic use of blue-light-blocking glasses during the shift, blackout curtains for daytime sleep, and morning light exposure on days off can help maintain circadian function within the constraints of an imperfect schedule. It’s about doing the best you can with what you have, and adjusting as circumstances allow.

Where this connects

Light is one of those topics that seems niche until you realize how deeply it connects to everything else. Circadian disruption worsens insulin resistance. Poor sleep from melatonin suppression amplifies the stress loop that so many people are already stuck in. Vitamin D insufficiency—whether from lack of sunlight or inadequate supplementation—affects immune function, bone density, mood regulation, and hormonal signaling. The modern environment that supports sickness and discourages health includes the light environment just as much as the food environment.

We didn’t evolve under fluorescent lights and blue-light-emitting screens. For most of human existence, the light we received was the light the sun provided—varied in intensity and spectrum across the day, absent at night. The body still expects that pattern. When it gets something radically different, the downstream effects show up in ways that most people never trace back to the source.

I don’t think this has to be complicated. Morning light. Midday sun when you can get it. Dim evenings. Dark sleep. That’s the foundation—and in my experience, it shifts things faster than most people expect.

I hope this connects some dots and gives you a practical place to start. Light is genuinely one of those levers where a small change in awareness leads to a meaningful change in how you feel.

Sources

  • Kováčová K, et al. “Daylight spectrum and intensity reduction and its impact on melatonin, cortisol, alpha-amylase, sleep parameters and sleepiness in humans.” Chronobiology International, 2025. 10.1080/07420528.2025.2556842

Rance Edwards is a National Board Certified Health and Wellness Coach (NBC-HWC) with over 2,000 clinical hours of experience, specializing in chronic disease management and lifestyle medicine.

If you’re wondering how light, sleep, and circadian health fit into your bigger metabolic picture, I’d love to talk it through. Book a free discovery call—no pressure, just a conversation about where you are and what might make a difference.