I’m extremely interested in showing you tiny changes that you can easily make, that deliver massively outsized returns for your health.
And when it comes to sleep, exposure to light has a huge impact and I want to show you some small changes that you can implement.
I’m not talking about blue light from your phone. Instead, I want to cover how a certain kind of light at a precise time of day has an outsized impact in improving your sleep.
Table of Contents
The Impact of Light on Sleep
Scientists first became aware of how light connects to sleep about 100 years ago. The first researcher to concentrate on sleep, Nathaniel Kleitman, even spent a month deep within a cave to see how the absence of light affected sleep cycles.
And one of the things we’ve discovered is the significance of outdoor light. A European study from 2003 looked at when people go to sleep and the amount of time participants had spent outdoors. They discovered a strong relationship. More time outside correlated with an earlier bedtime [1].
But this isn’t the only effect of outdoor light. Exposure also increases sleep duration and boosts sleep quality [2].
In one study, researchers compared two groups of office workers. One group worked in a space without windows while the other group had them. The group without windows had poorer overall sleep quality with more sleep disturbances. They also slept for a shorter time on average [3].
But those office workers without windows weren’t working in the dark. Why is daylight — as opposed to artificial light — significant? One key factor is brightness. Outside, light intensity can range from 10,000 lux to several times that. In contrast, indoor light is often below 400 lux [1].
We’ll come back to why this matters in a moment.
It’s also important to understand that the timing of light exposure matters, too. A study of college students measured the impact of bright light in the morning. The researchers found it improved a variety of measures of sleep quality [4].
So this study shows us that morning light is effective. But it didn’t compare the impact of light exposure at different times of day.
Another study that focused on office workers took timing into account. Scientists had participants wear a monitor that measured light exposure throughout the day. Consistent with other studies, high levels of the right kind of light during the whole day were associated with better sleep [5].
They also discovered that those getting high light exposure specifically in the morning had better sleep compared to those who didn’t [5].
And a new study from last year adds one more piece of evidence. Researchers took a look at how the timing of sunlight exposure related to sleep quality. They found again that morning sunlight exposure seemed decisive for sleep quality that night [6].
So the evidence shows getting bright light — like that found outside — in the morning can significantly boost markers of sleep quality.
But is this a big deal? What does better sleep end up meaning for our health?
Research has connected getting adequate sleep to a surprising number of health outcomes.
A study investigated sleep in relation to the development of metabolic syndrome. This is a cluster of conditions that raise our risks for heart disease, stroke, and type 2 diabetes. They tracked 3,000 people for five years. Individuals who slept 6 hours or less a night were most likely to develop metabolic syndrome [7].
Sleep also seems to impact the immune system. In one study, participants tracked their sleep and then were exposed to a cold virus. Those who got less than 7 hours on average were nearly 3 times more likely to catch a cold than those who got 8 hours or more [8].
All this means we should be doing everything we can to improve our sleep. So we’re going to look at exactly how to get that morning sun the research highlights as crucial.
Mechanisms
But first, let’s take a closer look at the mechanism involved. Why is sunlight, especially in the morning, linked to our sleep quality? Understanding this will help us take the most strategic approach.
Humans, just like other animals, follow a cycle over the course of a 24-hour day. Called the circadian rhythm, it consists of a daytime, awake period and a nighttime, asleep period. This cycle affects a ton of important body processes, like digestion, hormone production, and cellular repair. It’s controlled by a master clock in our brains. And this clock gets set by light — and its absence — through special receptors in our eyes.
So how does this clock control the cycle of sleep and waking? It does so partly by regulating melatonin production. Melatonin is a hormone that promotes sleep. When the receptors in our eyes detect the right kind of light, that sends a signal to the clock to shut off melatonin production. At the same time, light triggers the release of cortisol and other hormones that increase alertness. With growing darkness, this process reverses.
But what makes morning light special? The light receptors in the eye responsible for signaling the master clock that controls our circadian rhythm are tuned to short wavelengths of light. In other words, they are more sensitive to blueish light [2].
And while natural light has a broad spectrum of wavelengths, the relative amounts shift during the day. In the morning, there is more short-wavelength blue light. In the afternoon, the spectrum shifts to more red light [9].
So that means the kind of light that tells our brains it’s time to be awake is strongest in the morning sunlight. And sunlight also gives us a much brighter light source than indoor lighting.
A recent study brought these dynamics of light color and light intensity together to demonstrate their impact. Researchers tested the effects of bright white light, very dim white light, red light, and blue light on cortisol levels. This is a key hormone that rises in the morning to move us into daytime mode.
They found the bright white light and blue light boosted cortisol levels. The other lights did not [10].
Practical Stuff
So now it’s time to get practical. What strategies can we use to get more morning sunlight that has the ideal wavelength and intensity to improve sleep? How much do we need? And what about safety?
It might sound strange to talk about strategies here. Can’t we just go outside and stand in the sun? Well, personally, I find I have more luck starting a new habit if I have some specific ways to go about it. If that’s you, too, here are six things you can try.
1. Open your curtains as soon as you wake up.
You don’t have to be outside to get morning light. Let as much in through your windows as possible.
Also, consider using blackout or room-darkening curtains. We’ve been talking about the impact of morning sunlight and how it helps us wake up. The flip side is that we want to avoid light at night. Research has found that exposure to light during the hours of sleep is correlated with a host of negative health impacts [11].
We want to keep light in the bedroom to a minimum. Blackout or room-darkening curtains are an effective way to keep out unwanted light from outside your home.
2. Combine sunlight exposure with another task.
When we want to make something a habit, it’s a smart strategy to link it to something we already do anyway. We’re much more likely to consistently do it. Plus, this often allows us to take on a new habit without actually adding any time to our already busy schedules.
For example, consider eating your breakfast by a window or, if the weather is suitable, outside. Breakfast really is the most important meal of the day. Combining breakfast with morning sun exposure lets you kill two birds with one stone.
3. Park farther away from your place of work.
This forces you to walk a bit, and you’ll spend that time exposed to the morning sun.
4. Avoid using sunglasses for the first hour after you’re out of the house.
Let that wonderful morning light reach your eyes. Remember, the light receptors that regulate our circadian rhythm are in our eyes and brightness matters. Sunglasses will make the light less intense and blunt its impact.
5. Consider a light therapy device.
Natural morning light is ideal, but depending on your living situation or if you’re a shift worker, it can be difficult to have exposure to natural morning light. We can reap similar benefits in terms of sleep by using a light therapy device. One of the studies we looked at earlier, showing the benefits of morning light with college students, used a device like this [4]. These devices are specifically designed to have the right intensity of light to trigger a response. Look for a product with at least 10,000 lux.
How much light do we actually need? This is an area where we lack a strong consensus. One of the studies on sunlight exposure and sleep didn’t find a clear link between the length of light exposure and sleep quality [6].
On the other hand, there is a fair amount of research on the use of light therapy devices to treat seasonal depression, which is linked to light exposure. The theory about why this works is that depressed mood can be caused by problems with our circadian rhythm. Using light therapy helps to set that master clock properly. So it makes sense that the amount of light recommended for those suffering from seasonal depression could point us toward the right exposure, too. A typical recommendation is 30 minutes with a 10,000 lux lamp [12].
And a 2024 study found an hour or more in daylight during winter protected against depressive symptoms [13].
Taking the evidence together, somewhere between 30 minutes and an hour of morning sun is likely to be enough. It might be that even shorter doses are helpful, though. We’ll have to keep an eye on the research to zero in on the right number.
But talking about an hour in the sun is probably setting off alarm bells for some of us when thinking of UV radiation. So let’s consider safety.
First of all, this shouldn’t be an issue with light-therapy lamps, since commercially available options are generally designed to eliminate UV light, which is the wavelength we need to avoid.
But what about natural sunlight? Keep in mind that the impact on our sleep works through light receptors in our eyes. We should cover up and wear sunblock to protect our skin. That’s not going to interfere with the benefits. Plus, morning sunlight has less intense UV rays, so it’s not nearly as dangerous as midday sun. And for an extra measure of caution, clear UV-blocking lenses are available that won’t dim the light reaching our eyes.
Reference List
1. https://journals.sagepub.com/doi/10.1177/0748730402239679
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC6751071/
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC4031400/
4. https://pubmed.ncbi.nlm.nih.gov/36058557/
5. https://www.sleephealthjournal.org/article/S2352-7218(17)30041-4/abstract
6. https://journals.sagepub.com/doi/10.1177/13591053241262643
7. https://pubmed.ncbi.nlm.nih.gov/33621789/
8. https://pubmed.ncbi.nlm.nih.gov/19139325/
9. https://journals.sagepub.com/doi/10.1177/14771535211021064
10. https://www.tandfonline.com/doi/full/10.1080/10253890.2020.1803265?src=recsys
11. https://pmc.ncbi.nlm.nih.gov/articles/PMC9995772/
12. https://pmc.ncbi.nlm.nih.gov/articles/PMC543845/
13. https://www.sciencedirect.com/science/article/pii/S0160412023006864
