How our eyes are the key to unlocking our circadian clock
Sunrise and sunset are glorious natural wonders that happen every morning and every night. The rising and setting sun protrude gorgeous light that bounces off the clouds to create magical colors and shades, producing works of art twice a day. Yet because of our hectic, busy schedules, viewing the sunrise or sunset can feel like a special occasion, something we have to set aside time for. Our routines and jobs and responsibilities make us think that it’s something that can’t happen every day, twice a day.
It’s time we change that – science tells us that we must.
A reminder on the relationship between sleep and light
If you tuned into last week's blog post, you’ll know the benefits of getting sunlight into your eyes in the morning – how it sets your circadian clock and wakes you up for the day. Just as morning sunlight viewing starts your waking hours off right, evening sunlight viewing starts your sleeping hours off right. And it’s equally as important to keep your circadian rhythm happy and healthy.
Not just any evening light: sunset
This might sound familiar because setting and maintaining our biological, circadian clock is pretty symmetrical between AM and PM. According to many peer-reviewed studies, the ideal light to set our clocks in both the morning and night should enter our eyes at a low solar angle. This is because the necessary neurons for this process reside mostly in the bottom half of our retina and therefore, they view our upper vision field (look into “retinal optics” if you’re interested in learning more about this). The colors and angle of light around sunrise and sunset are exactly the light that our bodies were designed to react to. It should be viewed outside as it's fifty times less effective to view the light through a window (more on this later). Two to ten minutes of sunlight viewing is sufficient to activate our clocks.
At sunset, our melanopsin ganglion cells, the aforementioned neurons in our eyeballs responsible for setting our internal clock, signal to our brains, and thus our clock, that it’s the end of the day. A great study published last year tells us that viewing sunset light in the evening protects the mechanisms in our brain and body against the negative effects of light’s tendency to alter our melatonin levels later in the night.
These two signals – morning and evening sunlight viewing – and their ability to let our bodies know when it’s morning and night are extremely powerful for our overall health and wellness.
A closer look at eyes
To best understand why viewing sunlight outside is so crucial to systems throughout our entire bodies, we must dive deeper into the science behind our eyes.
Let’s look at a tangential example – in order to properly digest food and receive the nutrients it provides, you insert food into your mouth, chew it, swallow it, and your internal organs then distribute the nutrients throughout the entire body. The mouth is the receptacle for the information food adds to our bodies. Our eyes are the receptacle for the information light adds to our bodies.
Every cell in our bodies needs light information. They get that information through our eyeballs, specifically in the morning and evening. An amazing, repeated study from Science explained how there are no extraocular photoreception mechanisms in humans – light through eyeballs is the only way for our bodies to get this information. In fact, inviting light information to set our central clocks was the original purpose for our eye sockets – all other vision, such as pattern and color, came much later in the evolution of humans.
Eyes are fascinating, complex body parts with countless functions, but as it relates to our sleep, their ability to receive light information is central to setting the circadian clocks that dictate our sleep and contribute greatly to our overall health.
Hacks for optimal evening light viewing
Once you’ve completed your evening sunset viewing outside, there are ways to further avoid improper activation of those melanopsin ganglion cells. Light placement is key – it’s better to place the lighting lower in your physical environment. Lights at the table level or on the floor are far more conducive to these processes than overhead lighting, especially fluorescent overhead lighting, which you should try to avoid completely after the sun goes down. In order to keep your circadian rhythm in tip-top shape, it’s best if you’re able to avoid screens after sunset entirely. But if you find yourself scrolling on your phone or catching up on the latest Netflix show, it's recommended to wear blue blockers and dim the screen.
Starting and ending your day with sunlight shouldn’t be a rarity – it should be an everyday habit. Not only does the pure beauty they emit elicit joy and wonder, it will also ensure your circadian clock is tick-tocking at the proper rhythm, leaving you with your very best sleep.