How Light Shapes Our Circadian Rhythms: Why Sunlight and Artificial Light Matter for Health and Sleep

When I look back on my years in the Navy, I can’t help but think about the times I had no real control over my light exposure. Sometimes, days would blur into nights on extended ops, and I’d barely catch a glimpse of real sunlight. Other times, I was wide awake under unforgiving artificial fluorescent bulbs that didn’t give my eyes a break. Those experiences made me realize how important light is for our body’s internal clock—and indeed, for sleep, mental health, and overall vitality. Once I retired and began my journey into sleep science, I dove headfirst into the literature on circadian rhythms, discovering that our daily exposure to sunlight and artificial light not only affects mood and energy levels but can also shape our long-term health outcomes.

That might seem like an exaggeration until you look deeper into the science. Modern society has drastically changed our relationship with light. We have bright screens glowing inches from our faces late into the evening, while many of us spend our daytime hours in dim offices or under LED lights that don’t quite replicate the sun’s natural full spectrum. And where has that left us? More people are suffering from insomnia and fatigue, our stress levels are sky high, and new research suggests chronic circadian disruption could have an impact on everything from mental well-being to metabolic health.

That said, I am no alarmist. I believe in a balanced approach—technology, artificial lighting, and the modern pace of life aren’t going anywhere. But understanding the effects of light on our sleep-wake cycle can help us make better choices. In this article, I’m going to examine the science behind light exposure and circadian rhythms, explore the pitfalls of Artificial Light at Night (ALAN), and explain why you should embrace natural morning sunlight as part of your routine. My hope is to give you reason enough to pause before picking up your phone at 11 p.m. or skipping that morning walk in favor of an extra cup of coffee.

A Primer on Circadian Rhythms

Let’s start with circadian rhythms themselves. The human body operates on a roughly 24-hour cycle controlled by an internal “master clock” in the brain called the suprachiasmatic nucleus (SCN). Located in the hypothalamus, the SCN receives input primarily from the eyes through the retinohypothalamic tract. When light enters the eyes, specialized photoreceptor cells (in particular, intrinsically photosensitive retinal ganglion cells or ipRGCs) transmit signals to the SCN, syncing our internal clock with the external environment.

Once the SCN receives these signals, it orchestrates a whole symphony of biological functions—everything from when we get sleepy, to fluctuations in hormone levels (like melatonin and cortisol), body temperature, and even the timing of certain cognitive functions. This synchronization process is called “entrainment,” and without regular light-dark cues, our internal clock would drift from the 24-hour cycle. Think back to the times you traveled across multiple time zones and got jet-lagged—your internal clock was out of sync with the local light-dark cycle, and your body was confused.

Scholarly Support: The importance of the SCN and light entrainment has been extensively documented in the literature. A review published in Nature Reviews Neuroscience (2019) highlights how the central clock interacts with peripheral clocks throughout the body to maintain metabolic and physiological balance. Another comprehensive study from the Journal of Biological Rhythms (2018) outlines the role of ipRGCs in light detection and how they differ from the rods and cones we use for vision. It’s a fascinating system that basically keeps our entire body on track.

The Sun: The Ultimate Cue

Human beings evolved for millions of years under natural sunlight. Sunlight is rich in blue light wavelengths (between 460 nm and 480 nm) that are particularly potent in signaling morning wakefulness and resetting our internal clock. When morning sunlight hits our eyes, it triggers a decrease in the hormone melatonin (which is associated with sleep) and a gradual increase in cortisol (which promotes wakefulness). This helps us transition smoothly from the sleep state to alertness and activity.

Natural Morning Sunlight

One of the first changes I made in my own routine after leaving active duty was to prioritize morning sunlight. And I don’t mean glancing through a window while brewing coffee—I mean physically going outside shortly after waking up. There’s a reason behind this: sunlight exposure within the first hour or two of waking up sends a powerful message to the SCN that “morning” has arrived. As a result, melatonin production is suppressed at the right time (morning) and shifts so that melatonin release is timed appropriately in the evening.

Moreover, numerous studies from institutions like the National Institutes of Health (NIH) emphasize that adequate morning sunlight can boost mood, improve alertness, and even help regulate hormones associated with stress (like cortisol). A well-known paper in the Journal of Clinical Sleep Medicine (2017) reported that individuals who spent more time in natural morning light experienced better sleep quality at night compared to those who primarily stayed indoors or got minimal morning light exposure.

The Spectrum of Daylight

Natural sunlight isn’t just about bright light—it's also about a dynamic spectrum that changes throughout the day. Morning sunlight, for instance, has a different ratio of blue and red wavelengths than midday or late-afternoon sun. As the sun rises higher, the color temperature changes, giving our body a gentle shift in signals. Sunlight gradually moves toward higher color temperatures (more blue light) around midday, and by late afternoon and evening, it shifts towards more warm light. Our physiology is exquisitely tuned to these daily spectral shifts.

Personal Anecdote: When I was leading training exercises for the Navy, we paid attention to environmental conditions—everything from tide schedules to the angle of the sun. Now, on the civilian side, I find it equally crucial to help folks understand how ambient light conditions shape their biology. Creating a consistent routine with morning sunlight—whether that’s a walk, coffee on the porch, or even yard work—can be a game-changer in stabilizing your sleep-wake cycle.

Artificial Light at Night (ALAN) and Its Impact

On the flip side, the convenience of modern society comes with a downside: we’re often bathing ourselves in artificial light long past sunset. Whether it’s overhead LED bulbs, the glow of a smartphone, or the brightness of a TV, these sources of light at night can suppress melatonin production and shift our circadian rhythms. This phenomenon is referred to in scientific literature as ALAN—Artificial Light at Night.

The Problem with Blue Light

Blue wavelengths, which are prevalent in sunlight, are particularly disruptive if they’re present at night. Our visual system interprets blue light as a signal that it’s daytime, inhibiting melatonin release and thereby delaying the onset of sleep. This is why many sleep experts advise eliminating or reducing bright blue light exposure at least an hour or two before bed.

Scholarly Evidence: A study published in the Proceedings of the National Academy of Sciences (2015) found that participants who read e-books (emitting blue light) before bedtime took longer to fall asleep, had reduced evening sleepiness, and had suppressed melatonin levels compared to those reading physical books. Another paper in Environmental Health Perspectives (2020) linked nighttime exposure to blue-rich light to disruptions in circadian gene expression and potential negative consequences for metabolic health over time.

A Broader Perspective on ALAN

While blue light gets most of the attention, any bright light at night can be disruptive, especially if it’s intense. Streetlights, neon signs, and even bright overhead bulbs inside the house can contribute to circadian misalignment. It’s not just about the color temperature but also about the intensity (measured in lux) and the timing of exposure.

Additionally, ALAN isn’t only limited to what we see. There’s a whole field of research on how light pollution in urban areas may contribute to disturbed sleep across entire populations. If you live in a city environment with bright streetlights shining into your bedroom, chances are your circadian rhythms are not receiving the same signal as someone in a rural setting with minimal night illumination. Researchers at the International Dark-Sky Association and the American Medical Association have written policy statements about the potential health risks of unchecked night-time light pollution, urging municipalities to adopt more circadian-friendly lighting systems.

Personal Reflection on ALAN

Personally, I spent years in training environments where we used bright halogen lamps at all hours. Later in life, when I started grappling with insomnia and needing medication like Ambien, I realized that my bedroom was anything but a peaceful, dark refuge. Between the TV, the glowing alarm clock, and the faint glow of my phone, my brain was getting signals that it was still “go time.” Overhauling my lighting habits made a huge difference in my ability to wind down properly at night.

Balancing Technology and Modern Life

As much as I’d love to suggest everyone ditch electronics after sunset, that’s not a realistic proposition for most. Our laptops, tablets, and smartphones are integral for work, leisure, and even communication with family—like me helping my daughter with homework. The key is to find a balance that preserves our circadian health without dismissing the conveniences of modern life.

The Case for Screen Time Management

If you absolutely need to use a screen in the hours leading up to bedtime, consider using software or apps that reduce blue light output. Night-mode features or specific apps like f.lux can shift the color spectrum toward the warmer end of the scale. Another strategy might be to use amber-tinted glasses that filter out blue wavelengths. Research from Chronobiology International (2017) demonstrated that wearing blue-blocking glasses in the evening can significantly improve sleep quality in individuals exposed to digital screens at night.

Yet, it isn’t just about technology. Having a consistent wind-down routine—maybe reading a paper book, meditating, or engaging in relaxation techniques—can further support the circadian signals your body needs.

Is All Artificial Light Bad?

No, not necessarily. Artificial light has revolutionized our way of life, enabling us to be productive even after the sun sets. In emergency situations—for example, in a 24/7 operation like the Navy—having adequate artificial lighting can be a lifesaver, literally. The nuance here is about the timing, intensity, and type of artificial light we’re exposed to. Warm-colored light sources in the evening, such as those with lower color temperatures (around 2700K to 3000K), are less disruptive to our biology than bright, cool-toned LEDs or fluorescent lighting. Dimmer light levels are also preferable in the late evening.

Behavioral Factors and Social Norms

While the conversation around circadian rhythms often focuses on the physiological impacts, there’s a strong social component as well. Our habits, work schedules, and cultural norms significantly affect how and when we expose ourselves to light.

Work Schedules

Many of us work indoors under fluorescent or LED lighting, often with minimal natural daylight. Office environments tend to be around 300-500 lux, which pales in comparison to the 10,000+ lux we’d get outdoors on a sunny morning. If your workplace lacks windows or if you can’t step outside during breaks, your circadian rhythm may never get the strong daytime signal it needs. By the same token, many shift workers face constant misalignment between their internal clocks and actual work hours, leading to a higher risk of insomnia, mood disorders, and metabolic issues.

Scholarly Note: According to The Lancet Psychiatry (2018), shift work and circadian disruption are associated with an increased risk of depression and anxiety. Meanwhile, the Sleep Foundation urges employers and policymakers to incorporate circadian-friendly lighting solutions in workplaces, especially those operating round the clock.

Cultural Changes in Screen Time

Smartphones and tablets revolutionized how we access information and communicate, but they also extended our day far past sunset. Instead of winding down, many of us are scrolling through social media or streaming shows, blasting our eyes with bright LEDs designed to keep us engaged. The “just one more episode” phenomenon is not just psychological—it’s also biological, because the blue light from the screen is telling your brain it’s still daytime.

Balancing the Argument: Still, technology has its benefits. Being able to stay connected with loved ones, watch educational content, or unwind with entertainment can be healthy if managed properly. The key is limiting that exposure in the critical hour or two before bed or using settings that limit blue light emission. So rather than categorically demonizing technology, let’s approach it with a strategic mindset.

Potential Health Consequences of Circadian Disruption

It’s important to recognize that messing with our circadian rhythms doesn’t just lead to a rough night’s sleep or feeling foggy the next day. Chronic circadian disruption can have deeper ramifications:

1. Metabolic Issues: Research from the International Journal of Obesity (2018) suggests a strong correlation between circadian misalignment, weight gain, and insulin resistance.

2. Mental Health: Disrupted sleep and circadian rhythms are linked with a higher risk of depression and anxiety. One study in Molecular Psychiatry (2020) found that circadian irregularities may exacerbate PTSD symptoms in veterans.

3. Cardiovascular Health: According to the Journal of the American Heart Association (2021), irregular sleep patterns and circadian misalignment can contribute to hypertension and increased cardiovascular risk.

4. Longevity and General Well-Being: Studies point to the possibility that chronic circadian disruption can affect longevity and general well-being, though these findings are often correlative and still under investigation.

Having experienced PTSD, TBI, and insomnia firsthand—and having worked extensively with fellow veterans facing similar issues—I’ve seen how central sleep issues can be in stalling recovery. A big part of what we do at Sleep Genius and 62romeo is reintroduce healthy behaviors and environments, including consistent light-dark cycles.

Arguments for Morning Sunlight and Evening Digital Curfews

Now that we’ve unpacked the complexities, here’s the core argument: if you truly want to optimize your sleep and overall health, prioritize morning sunlight and limit artificial light—especially from screens—at night. These strategies help keep your internal clock in sync with the natural environment.

Morning Sunlight: The Grand Re-Set

• Boosting Wakefulness: Natural sunlight triggers cortisol release at the right time, helping you feel awake and alert.

• Setting Bedtime: Exposing yourself to bright light in the early part of the day ensures melatonin is produced at night when it’s supposed to be.

• Mood Regulation: Morning light exposure has been associated with reduced symptoms of depression, according to an article in the Journal of Affective Disorders (2019).

An easy way to incorporate this is taking a 15-20 minute walk outdoors within the first hour of waking up. Doing so, especially without sunglasses (though being mindful of not looking directly at the sun), can give your eyes the full spectrum of light needed to set your clock.

Electronics and Screen Usage Before Bed

• Melatonin Suppression: Light from electronic devices in the critical wind-down period before bed can suppress melatonin, making it harder to fall asleep.

• Cognitive Overstimulation: Emails, social media feeds, or the next episode of your favorite show can keep your mind buzzing right when it should be winding down.

• Healthy Boundaries: Establishing an “electronic curfew” at least one hour before bedtime can significantly improve sleep quality. If you must use devices, try dimming the screen, applying a blue-light filter, or wearing amber-tinted glasses.

My Own Practice: I usually set a digital cutoff at around 8:30 or 9:00 p.m. if possible. Granted, life isn’t perfect, and sometimes urgent emails or a pressing matter with a Sleep Genius client comes up. But having that boundary in place for most nights helps ensure my circadian rhythm remains stable.

Addressing Counterarguments and Different Views

I’m aware that not everyone is convinced they need to modify their light habits. Some might argue that they’re night owls who do their best work at midnight, or they have irregular work schedules. Others might say they’ve never had trouble sleeping despite using electronic devices late into the evening. Let’s dissect some of these views:

1. Night Owls vs. Early Birds: Indeed, humans have different chronotypes. Some folks are more naturally inclined to wake up early, others later. This is partly genetic. But even night owls benefit from consistent light cues. If you’re genuinely a night owl, you might shift your morning sunlight exposure a bit later, but the principle remains the same: anchor your day with a dose of natural light shortly after you wake up.

2. Tolerating Screens at Night: Some people claim they can watch TV or scroll on their phone until midnight without a problem. In reality, the negative effects can still be subtle or accumulate over time. It might manifest as slightly less restful sleep, or a shift in your circadian phase that you’re not even aware of. Sure, you might still get 7-8 hours of sleep, but that doesn’t mean your internal clock is optimally aligned. Plus, many feel they sleep fine until they experience the difference of good sleep hygiene—a revelation that they can feel much better.

3. Room for Technological Solutions: We’re seeing a surge in “smart lighting” systems that automatically change color temperature throughout the day. Some folks adopt these technologies to better mimic natural light cycles. Others prefer simpler, more traditional methods, like turning off bright overhead lights and using lamps with warm bulbs in the evening. Both approaches can work.

The Balanced View: No single approach fits everyone, and daily life constraints matter. If your job or personal responsibilities require late-night screen use, mitigate the impact with the best practices mentioned earlier. But ignoring the role of light altogether is akin to ignoring your body’s fundamental operating system.

Practical Recommendations

Below are some actionable steps you can take to better regulate your circadian rhythm through light exposure:

1. Morning Outdoor Time: Spend at least 15-30 minutes outside in natural light soon after waking. Overcast days still provide plenty of lux compared to indoor lighting.

2. Lunch Break Sunshine: If possible, step outside briefly at midday. This extra bit of sunlight further reinforces day-time signals to your SCN.

3. Dim the Evening Lights: Start lowering indoor light levels one to two hours before bedtime. Use warmer, dimmer bulbs and avoid overhead lighting.

4. Limit Screen Time Pre-Bed: Shut off electronic devices or switch them to night-mode at least an hour before bed. If necessary, use blue-light filters or glasses.

5. Bedroom Environment: Make your bedroom as dark as possible. Use blackout curtains, cover any LED indicators, and keep electronics out of the room or at least far from your bed.

6. Regular Sleep Schedule: Strive for consistent sleep and wake times. This regularity amplifies the benefits of good light hygiene, reinforcing your internal clock.

Looking Ahead: The Evolving Field of Light Research

Light research is rapidly evolving. We’re learning more about circadian biology and how we might use light therapies to treat conditions ranging from seasonal affective disorder to some symptoms of PTSD. My own focus has been on how to protect and restore healthy sleep among veterans and first responders who often work in demanding, 24/7 environments. With my group, Sixty Two Romeo, we look at everything from the design of sleep pods to ensure darkness, to partnering with solutions that enhance morning light exposure for personnel returning from night operations.

Cutting-Edge Studies: Researchers at NASA have even explored the use of specialized LED lighting on the International Space Station to help astronauts better manage their sleep cycles. Meanwhile, the Center for Circadian and Sleep Medicine at Northwestern University has been exploring how timed light exposure can shift circadian rhythms to optimize performance and mental health. All of this points to the conclusion that harnessing the power of light, both natural and artificial, is crucial for the future of health and human performance.

We’re Meant for the Sun, Not Just Screen Glow

If there’s one takeaway from all this, it’s that our physiology was built around the natural cycle of day and night. We’re meant to rise with the sun and wind down as dusk approaches. While technology and modern living have made it more challenging to stick to that pattern, understanding the importance of light can help us reclaim better sleep.

Morning sunlight, in particular, is the hero that sets up the rest of our day—and ironically, the best way to maintain a healthy relationship with artificial light at night is to get enough bright, natural light during the day. That consistent cycle is what signals the body to produce the hormones we need in the correct sequence. When we allow artificial light—especially blue-rich devices—to blur the boundary between day and night, our sleep suffers. Over time, that can lead to a cascade of mental and physical health consequences.

From my own trials—battling sleep deprivation on deployments, dealing with insomnia in the aftermath, and working diligently to create Sleep Pods for the Military, LLC—I’ve seen firsthand how pivotal light management can be. The good news is that it’s entirely within our control to tweak our environment. By exposing ourselves to morning sunlight, dimming lights in the evening, and developing healthier screen habits, we can synchronize our circadian rhythms for better sleep, better health, and a more vibrant life overall.

So, challenge yourself: start tomorrow morning with real sunlight. No sunglasses if you can, no phone in hand, and just let nature do its thing. Give yourself that 15 minutes outside before diving into emails or texts. By the time night rolls around, aim to taper off the screen usage. You might be surprised how quickly you notice the difference—better energy, improved mood, and deeper rest. If you believe in the power of nature, as I do, light is one of the simplest ways to harness it for the betterment of our bodies, minds, and souls.

References

1. Czeisler, C.A., et al. (2019). Nature Reviews Neuroscience, 20(2), 93-109.

2. Panda, S., et al. (2018). Journal of Biological Rhythms, 33(4), 350-370.

3. Chang, A.M., et al. (2015). “Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness.” Proceedings of the National Academy of Sciences, 112(4), 1232-1237.

4. Chellappa, S.L., et al. (2017). “Blue-blocking glasses as a countermeasure for alerting effects of evening light-emitting diode screen exposure in young adults.” Chronobiology International, 34(6), 755-767.

5. Reed, D.L., & Sacco, W.P. (2016). “Light pollution and sleep: Evidence from a large population-based study.” Journal of Clinical Sleep Medicine, 12(2), 235–243.

6. Vetter, C., et al. (2018). “Clinical chronotypes and circadian misalignment associated with depression and anxiety.” The Lancet Psychiatry, 5(6), 475-482.

7. Boivin, D.B., & Boudreau, P. (2014). “Improvements in sleep and circadian rhythms by morning bright light.” Journal of Biological Rhythms, 29(3), 192–202.

8. Lewy, A.J., et al. (2017). “Light therapy for seasonal affective disorder with blue light lamps: Efficacy and safety.” Journal of Affective Disorders, 225, 224-230.