Let’s Talk Light and the Circadian Rhythm
Light is a powerful regulator of our circadian rhythm, and modern life really messes things up!
I talk about light a lot with the families I support. The knowledge that light is a powerful regulator of the circadian rhythm is a basic part of my sleep hygiene recommendations. However, in February I participated in a sleep continuing education conference, and one of the presentations focused on light and the circadian rhythm. I had so many aha moments that I wanted to write this post to share a deeper dive into light and our circadian rhythm with you all.
So let’s take a deeper dive into our circadian rhythm, light, and our sleep.
Warning, this might be a bit science-y, but hopefully it will be nice and clear. Most of the info I’m sharing with you comes from a professional talk by Carrie Bennett, MS and also the work of Dr. Andrew Huberman.
First off, let’s define the circadian rhythm. The circadian rhythm is our brain’s internal clock. It regulates our day night cycle, sleep, hormones, gene expression, body temperature, and so much more. Two circadian linked hormones are important in understanding sleep, melatonin, and cortisol. The body releases Melatonin when the light begins to dim in the evening, and too much bright light in the evening can inhibit its release. Melatonin helps you feel sleepy, affects your sleep cycles, and influences cell repair. Cortisol is highest in the morning, helping you wake up and be alert throughout the day. It is also a stress hormone released when you are dysregulated. So we want melatonin overnight and cortisol during the day – and neither hormone around when it’s not supposed to be there.
The signal that kicks off our circadian rhythm is light, specifically morning light. And the signal that we are headed into nighttime is the dimming of the light. Throughout the day, our bodies expect a specific sequence of light wavelengths as the day progresses from sun rise, to mid-day, to sunset, and then nighttime. That sequence helps organize our circadian rhythm and in turn the functioning of our body systems. A healthy circadian rhythm relies on the right cues at the right time to stay in sync with the natural day night cycle.
Once upon a time, sunlight truly shaped our day. Our biology was in sync with the natural daylight cycle. Now it is not. Artificial light means that we are able to scramble the natural light patterns, and confuse our bodies, undermining our circadian rhythm, sleep, and health.
Sunlight has different wave lengths throughout the day including the classic rainbow colors, infrared, and ultraviolet. Through sensors in both our eyes and our skin, the body detects the distribution of light, syncing our body with the earth’s day night cycle. This is a key part of supporting your circadian rhythm. A healthy circadian rhythm isn’t simply a regular day night cycle for your body, but a regular day night cycle in rhythm with the actual day night cycle of the environment.
Dawn light: Before sunrise, the light is heavy on red and infrared frequencies. This light is soothing, healing, and anti-inflammatory.
Sunrise light: As the sun breaks the horizon, there is a spike in blue light. This blue light frequency sets the circadian rhythm. It’s this morning light that anchors the circadian rhythm and syncs all other bodily tasks.
Morning light: When the sun is between 10-30 degrees above the horizon, UVA light begins to appear. UVA light reacts with key amino acids to support the production of critical hormones that are key for energy, mental health, sleep, and cell repair.
Daytime light: Intensity peaks until solar noon and then gradually lessens as you move through the afternoon.
Sunset light: As the sun sets, we get back to the red and infrared light similar to dawn. The blue light fades as red and infrared light becomes present and shifts to dark. This shift signals the body to produce melatonin, which often peaks a couple hours later (assuming no artificial light interferes).
Nighttime: No blue light should be present. Even small exposures to blue light overnight can breakdown melatonin and trigger a cortisol spike.
The body needs exposure to light throughout the day, but the morning light is particularly important for supporting your circadian rhythm and sleep. For the body to register the appropriate wave lengths, you need to be outside, experiencing the light with naked eyes (meaning not through windows, glasses, or contacts). If you can’t get outside, open a window. The glass filters out some of the wavelengths, but light coming through the open window works when getting outside isn’t possible. It is this morning light that anchors your circadian rhythm. Ideally this anchor comes at sunrise, but morning light is key even if it’s not sunrise light.
Additionally, the morning UVA light is a powerful signal to your body. The UVA light reacts with key amino acids to create some very important hormones that regulate your mood, focus, energy, and sleep. One of these hormones is serotonin. Serotonin not only regulates your mood, but it is a precursor to melatonin. So making more serotonin in the morning allows your body to produce more melatonin at night.
Morning light is one way to positively affect sleep quality. Managing your evening light exposure is another key piece of supporting your sleep. The absence of blue light in the evening is essential to allow your body to produce melatonin. Blue light wave lengths are present in many light sources as well as being high in light from screens. Dim, warm lights in the evening are necessary to support melatonin production just as a dark overnight sleep space is important to maintain good sleep quality.
We disrupt our circadian rhythm in so many ways. We don’t get outside enough. We expose ourselves to high levels of blue light throughout the day and into the evening. Most people spend the majority of their day under artificial lights and in front of a screen, both of which confuse your circadian rhythm with the constant high level of blue light. In the evening, artificial lights, and screen use (TV, phone, computers/tablets) suppress melatonin production and increase cortisol – the exact opposite of what our body needs.
Fun fact from the professional presentation by Carrie Bennett, firelight suppresses melatonin by about 2%, old school incandescent light bulbs by about 40%, and bright LED lights by about 80%. Based on these numbers you can see how we’ve only made this problem worse as technology advances.
Disrupting our circadian rhythm undermines our sleep quality, but it also undermines our ability to repair during sleep. Remember melatonin helps you feel sleepy (along with sleep pressure) but it also supports key cell repair during deep sleep in the first half of the night. So we are talking about sleep quality but also about maintaining health.
Modern light is really bad for our sleep! What can we do to make light our friend to support better sleep (and better health)?
Some ways we can use light to support our circadian rhythm:
If you are awake before sunrise, use dim, warm colored lights, or wear blue light blockers.
If you are awake at sunrise, go outside for at least 3 minutes. Gaze towards the rising sun.
Get outside in the morning when the sun is between 10-30 degrees in the sky for that UVA light exposure. The Circadian app can help you figure this out.
If you miss sunrise, get natural light exposure as soon as you can, and ideally before the sun is 30 degrees above the horizon. Try for before 9am.
Get outside throughout the day to help your body sink with the light spectrum, even if it’s just a few minutes here and there.
Reduce high artificial blue wavelength light exposure during the day where you can. The constant source of blue wavelengths is confusing to our bodies. Choose natural light over artificial light if it is an option and try to filter out some of the blue light from your screens.
Watch the sunset when you can to give your body the signal that the day is ending.
Pick dim, warm colored lights in the evening. Bonus points if they are lower down – think table lamps verses overhead lights. Position in the visual field also affects how our body perceives the light.
Avoid all screens after sunset. If you are using them, use blue light blockers through filters on the device or wear blue light blocking glasses.
Create a dark room overnight. Even the smallest amount of light can disrupt the circadian rhythm.
And if you are sitting there, shaking your head, thinking there’s no way you can do all of that, I’m right there with you. It’s a bit overwhelming. So just focus on one thing at a time. Maybe it’s getting outside for regular morning light exposure as soon as you can after waking up. Or maybe it’s focusing on your evenings and changing out your light sources. Or mitigating screen use in the evening by some good blue light blocking options. These are all great starting points. Each small step towards more circadian rhythm friendly light choices adds up. Don’t let the pressure to do it all get in the way of just making one small change that feels manageable for your life right now.