Learn how light and dark affect sleep

Learn how light and dark affect sleep

Once you learn how light and dark affect sleep, it’s much easier to use these tools for all sorts of things. Working WITH your child’s body (instead of against it) can help you navigate sleep in the summer, adjust for daylight saving and make traveling easier, to name just a few. But I’ve gotten a bit ahead of myself. Let’s start with the basics of how light and dark affect sleep first. These basics have A LOT to do with how well you, your baby or your child, will sleep in general.

Here is the science stuff in plain English – but if you’re too tired to read the full blog, I’ve summarised the “too long; didn’t read” (TL;DR) at the end.

Humans are not nocturnal

Although there may be some “night owls” out there that disagree with me, human beings are not nocturnal creatures. We all know what nocturnal means, right? We use the word to refer to animals that sleep during the day and do most of their activities at night; the humble kiwi, bats, owls, opossums, and the Tasmanian devil for our friends across the ditch, are just some examples.

So, what’s the opposite of “nocturnal?”

We are!

Most of us are not nearly as familiar with the term “diurnal” (that’s the opposite of nocturnal BTW) yet, as humans, that’s exactly what we are. As a rule, we take care of business during the day, and get our much needed sleep in the dark; after the sun goes down. And we’re a significant minority in that regard. A little known fact is that around 80% of mammals evolved to sleep during the day, not at night. But that’s a side note, so let’s move on.

We’re built to be awake in light

Biologically, humans are built to do our modern-day version of hunting and gathering, awake, in daylight. We’re simply not built for the dark. For a start, our eyes don’t adapt to the dark very well, we don’t have echolocation skills like a bat, and we rely on the sun for our vitamin D.

But that’s OK, there are some great benefits that come with being daytime creatures. One of my favourite benefits is a thing called the circadian rhythm, or in layman’s terms, our body clock. It’s this internal rhythm that determines how light and dark affect sleep.

Benefits of the circadian rhythm

As you may already know, the circadian rhythm is the internal clock of the human body. This clock prompts us to wake up in the morning, and to go to sleep each night. And very much like an old fashioned mechanical clock, it has a LOT of moving parts. Except instead of gears and springs, it’s made up of stimuli and hormones.

The main hormones in our story of the circadian rhythm are melatonin and cortisol. If you have a baby or child who is not sleeping well, you have no doubt heard of both of these hormones; but there may be more to the story than you first realised.

Introducing Melatonin

Melatonin, often known as the sleepy hormone, is produced in the pineal gland of the brain, and one of its roles is to help the body relax, both mentally and physically. This hormone helps us both get to sleep AND stay asleep. Understanding how melatonin works helps us understand how light and dark affect sleep.

Melatonin production needs light

When your baby gets their needed 11-12 hour stretch of sleep (glorious sleep), you can thank their pineal gland for firing up those melatonin pumps. But you can also thank daylight, because exposure to the sun stimulates melatonin production. That’s production, mind you. There’s a little more to the secretion of melatonin. We’ll talk about that soon. But the buildup of the melatonin hormone itself is stimulated by exposure to sunlight. So, it’s not just an old wives tale, getting your baby outside into sunlight during the day really does help him or her sleep better at night!

Melatonin release needs dark

Melatonin is also called the Dracula hormone because it only comes out in the dark (cute, huh).

Once nighttime rolls around and the sun goes down, our eyes stop taking in light, and the brain responds by releasing those stores of melatonin that it built up during the day. This melatonin release signals our muscles to relax, tells the brain to ease back on the thinking, and allows us humans to drift peacefully off to sleep, hopefully for a long, restful night.

In summary, to get a good sleep, we need the presence of melatonin, the sleepy hormone. But for melatonin to be fully effective, it requires the presence of both sunlight (to produce it) and darkness (to release it). Thus light, and dark.

And then we wake to start our day.

Introducing Cortisol

If Melatonin is our sleepy hormone, then cortisol is our waking hormone. Come morning, blue light from the sun starts to permeate the thin skin of our closed eyelids and this signals the brain that it’s time to wake up.

Our brain helps us get out of bed, shake off those cobwebs, and get on with our tasks for the day. It does that, in part, by telling our adrenal glands to pump out some cortisol. In the early hours of the morning, our bodies are naturally primed to release cortisol.

For those of us sensitive to light, even a sliver of light through the curtains can wake us.

It’s not just a stress hormone

Cortisol gets a bad rap these days because people associate it with stress. This is especially true if you have a baby who isn’t sleeping at home. If you start investigating baby sleep, you’ll no doubt have seen cortisol bandied about because crying, stress, and cortisol all get packaged together. Its why people are up and arms about “sleep training” because it is linked with baby crying, which is linked with stress and cortisol. That’s not at all what sleep training is about these days, but that’s another blog.

Maybe you’ve heard that babies cry because their cortisol levels are elevated and it’s causing them stress. Or maybe they’re stressed and that makes them cry, and that spikes their cortisol levels. Some combination of stress, cortisol, and crying, right? Whichever direction it goes, these comments put cortisol in a bad light. Too much of anything can be a bad thing, but with cortisol it’s not all bad.

Cortisol is beneficial

The truth is cortisol is a very beneficial hormone.

Cortisol regulates metabolism, blood pressure, and blood sugar, it suppresses inflammation, and regulates the body’s stress response. It’s not some toxic stimulant that causes us to freak out. It has a wealth of benefits, one of which is that it perks us up and keeps us alert during the day.

Cortisol levels surge when exposed to morning light, effectively kickstarting the waking/alert process and helping the body stay on track with its optimal circadian rhythm (awake during the day and asleep at night).

Light and dark worked, until it didn’t

This whole intricate dance between light and dark, cortisol and melatonin, and waking and sleeping, evolved over an incredibly long time. Indeed, it all worked like magic until relatively recently.

It all started going wrong when we discovered that we could pass an electric current along a filament and “artificially” illuminate our surroundings. Yep, the lightbulb has a lot to do with sleep issues. Before that, we relied exclusively on fire, and fire emits very little blue light.

What’s the deal with blue light?

Blue light is the frequency of natural sunlight (it’s why the sky is blue). And light bulbs, depending on their hue, emit quite a bit of it. So do TVs, LEDs, computer monitors, iPads, smartphones, and all of those other screens that surround us these days.

The modern world literally floods our eyes with blue light.

Unfortunately, all that blue light coming at us in hours when we would normally be enveloped in darkness tells the brain that it’s still daytime. As such it inhibits the release of melatonin, and makes it that much harder to get to sleep.

How can we minimise light to sleep?

Since we can’t reasonably get rid of all of the sources of blue light around us, the best thing to do for sleep (our children’s and ours) is turn off those really intense sources of blue light. Turning off TVs and smartphones a couple of hours before going to bed AND making sure the sleeping area is as dark as we can get it, really helps.

When I say dark, I’m talking really dark. 10/10, can’t see your hand in front of your face kind of dark. Blackout blinds (or these Sleepy Sunday’s blackout sheets) can be a game changer for sleep, especially in the summer.

And if you really CAN’T turn out the lights, at least invest in some modern day solutions like those at *.

That’s the story of light and dark

The circadian rhythm, and its daily heroic effort to keep us running at peak performance, is a fascinating little piece of our physiology. With just a little support and help from our side, it can work wonders. Both in getting us out of bed with energy and enthusiasm, AND helping us feel relaxed and peaceful when it’s time to sleep.

Learning how light and dark affect sleep, means we can work with our bodies instead of against it. If you take this onboard, I guarantee you’ll start seeing, and feeling, the results of better sleep immediately.

In summary (TL:DR)

  • Humans are diurnal (not nocturnal), built for daylight.
  • Our circadian rhythm (or body clock) tells us when to wake and when to sleep and is largely dependent on the hormones melatonin and cortisol.
  • Melatonin is our sleepy hormone; it helps us get to sleep and stay asleep.
  • Sunlight is necessary for melatonin PRODUCTION. Thus, our children (and all humans) need sun exposure during the day. But darkness is needed for melatonin RELEASE to prompt sleep.
  • Cortisol is our waking hormone, released in the early morning. It has amazing benefits, including keeping us alert.
  • All worked well for our body clock, with melatonin and cortisol and light and dark until the development of the light bulb. The lightbulb emits blue frequency light (like sunlight) and tricks the brain into thinking it’s daytime. So do screens.
  • Blue light (from sunlight, screens and bulbs) inhibits melatonin and makes it hard to sleep.
  • To sleep better (and work with our bodies), we need to turn off screens and bright lights hours before bed and make the sleep environment as dark as possible.
  • Working with our bodies, instead of against it, can help us all sleep better and wake refreshed.

And finally

When I work one-on-one with clients to set up healthy sleep habits and/or solve sleep issues, light and dark, are just ONE of the many things we cover. But it’s this scientific knowledge of our bodies and sleep, and how humans are designed, along with the developmental needs of our babies and children, that helps me work with all ages. And I may be the only sleep consultant in New Zealand who does this!

If sleep is on your mind because you’re lacking it – please check out the resources on my website. If you haven’t already, download my free tips for babies, toddlers or adults (and teens).

And if you’d like to know more about how I work, my sleep packages, or what’s going wrong with sleep, then book a FREE initial sleep evaluation call. I always LOVE to talk sleep!

*This blog contains affiliate links which mean I receive a small kickback when purchases are made through these links. Thank you for supporting my small business.