Over the course of 2018-19, I was involved in a research and writing project, a part of which fundamentally changed how I view the key drivers of day-to-day wellbeing in our societies. I was initially looking at the primary promoters and disrupters of sleep, and with respect to the disrupters, there was a major focus on light exposure at night. It is becoming increasingly understood that night-time exposure to blue spectrum light is a fundamental disrupter of sleep across all ages in our society. But what I was soon to realise was that as problematic as night-time light exposure is, a bigger issue is our distinct lack of light exposure during the day – a problem very few people are aware of.
To understand these issues and their importance, we need to step back from simply focusing on sleep as a key health behaviour to focusing on our circadian biology. Humans operate via distinct rhythms and cycles. While apparent when we consider something like menstrual cycles in women, many of our other rhythms and cycles have become lost in what I call the linearity of our modern world.
The cornerstone of our fundamental rhythms is our circadian rhythm – our 24-hour rhythm that is, or should be, tagged to the sun rising and setting. We also have roughly 90-minute cycles inside of this 24-hour cycle (known as ultradian rhythms). A woman’s menstrual cycle is a good example of an infradian rhythm – a rhythm greater than 24-hours. Sadly, in our modern society, we often aim to flatten many of these rhythms, expecting to be able to work continuously across the day with consistent energy rather than understanding that our energy levels oscillate on roughly 90-minute cycles. Behaviourally, in this example, in our low ebbs we’ll reach for caffeine/nicotine/sugar to keep pushing through rather than altering how we are working to match our biology.
Virtually all rhythms we have operating in our physiology are a part of the 24-hour circadian rhythm (our master rhythm, if you like). In the normal run of things, this 24-hour cycle would be tagged to two key synchronising events each day – sunrise and sunset. Indeed, this is how our physiology is inextricably linked to our environment. In simple terms, blue spectrum light is the specific portion of sunlight which stimulates our wakening state during the day, starting at sunrise. In the evening, after the sun sets, the absence of this light – darkness – drives a shift from wakefulness to sleepiness.
Circadian biology research is beginning to understand that we have quite distinct daytime and night-time physiologies, with the switch between the two governed by our light exposure patterns. Exposure to bright natural light stimulates, as you would expect, our daytime physiology. In day mode, we are (or should be) alert, active, and hungry. These states are driven by our key day mode neurotransmitters – cortisol, dopamine, and serotonin. As the sun sets and relative darkness takes hold, we transition to night mode. Our body temperature begins to lower from its peak of early evening, our metabolism falls, and our drive for sleep increases (or it should do at least).
With the darkness comes an increase in our melatonin levels – the hormone most commonly associated with initiating sleep (though it has many functions throughout our body and, in my opinion, is one of the most misunderstood and underrated hormones we have). It is perhaps more accurate to think of melatonin not as a sleep hormone, but as a darkness hormone. It is becoming more common knowledge that the light from our ubiquitous electronic devices is emitted largely in the same blue light spectrum as sunlight. It is perhaps at this point that you can see where problems might begin to occur.
If relative darkness is required in order to allow melatonin to rise and begin orchestrating the various physiological processes which occur as part of our dark physiology (including sleep), yet we are spending our night-time exposed to blue light emitting devices (sunlight emitting devices, in effect), then you can see why sleep can be so hard to come by. Even relatively small exposures to such intense light can delay your melatonin pulse significantly, with some research suggesting that as little as 30-minutes with your phone, laptop, or TV (often all three simultaneously) beaming intense blue light into your eyes can shift your melatonin pulse curve sideways by about two hours.
To illustrate this in a more real-world way, if you would normally be ready for sleep at 10pm but decided to spend your evening bathing in blue light prior to this, don’t be surprised if you are still struggling to initiate sleep well after midnight. If you can fall asleep, you might find yourself getting bounced out of it early on and struggling to slip into anything deeper than a light slumber. You may eventually get into a deep sleep around 3-5am, but here you are potentially only a couple of hours away from the alarm clock going off.
Being ripped out of deep sleep leads to that groggy feeling called sleep inertia. What should have been a restorative night’s sleep was anything but. It’s a feeling akin to jetlag, and unfortunately what I have described above is the norm for many (most?) in our modern world. But it is not blue light exposure at night that changed my views on wellness. It was the lack of blue light during the day that did.
For everything to work as it should, yes, we need relative darkness at night – much more than we typically afford ourselves. But we also need bright light exposure during the day, and it was this fact that is the missing piece of the puzzle for many of us. We are living in what I have come to call a light inversion. Our days are too dim and our nights too bright.
Sunlight contains full spectrum light – everything from UV light (where UVB is what we use to make vitamin D in our skin with), through to infrared light (which gives us the feeling of warmth). In the middle is the visible spectrum light, including the blue spectrum light. Receptors in our eyes (intrinsically photosensitive retinal ganglion cells – ipRGCs) that make up the light-receiving part of our circadian rhythm system, contain a vitamin A-derived protein pigment, melanopsin, that is maximally sensitive to intense blue wavelength light such that we get from sunlight not long after sunrise (peaking at wavelengths of 480nm as would occur at solar noon on a clear blue-sky day).
The blue-light stimulation of these receptors stimulates neural pathways in our brain, eventually triggering the release of neurotransmitters (such as serotonin and dopamine) and hormones (such as cortisol) which help increase our wakefulness and alertness, our body temperature, as well as suppress the synthesis of our primary night-time physiology hormone, melatonin. As the intensity of blue light declines toward the end of the day, being replaced, at first by visible red light (690nm wavelength; such as is seen at sunset, or emitted by fire light), and eventually darkness – melatonin production is increased initiating our sleep processes and helping us to, hopefully, fall asleep. Coordinating and synchronizing these light- and dark-triggered circadian rhythm events day after day is a key part of our brain, the suprachiasmatic nucleus (SCN), more commonly known as the master body clock.
Now here’s the rub. An increasing proportion of people – children and adults – spend more time than ever in human history indoors, under artificial lights. Rarely do these lights come even remotely close to being sufficiently intense to regulate the systems outlined above. You wouldn’t need to think about it for long to come up with a very long list of occupations where people are indoors all day, including an increasing number in buildings with virtually no natural light. In my research, I came across stats such as; most Americans spending 90% of their daytime hours indoors, or prisoners in Australia spending more time outdoors than the average Australian teenager. I’ve no doubt that the situation isn’t any different here in New Zealand.
To get a sense of the problem here, I purchased a light meter and began taking measurements. The specific intensity of a given light source in a given space is measured in lux (lumens is the measure of the brightness of a light at its source). I began taking readings in various workplaces and public spaces over the course of 2018. I was most interested by the readings I took over the winter period when it might be perceived as not being particularly bright outside, especially on a heavily overcast day.
From relatively early in the day, even in the depths of winter, and even with dark clouds filling the sky, the light intensity outdoors was always several thousand lux. At sunrise, the morning might start out at under 1000 lux, but would rapidly increase. The lowest measurements taken on the darkest of days came in around 3000 lux, but most often the readings were upward of 50000 lux, and on bright summer days, well over 100000 lux. But move indoors and things change very quickly.
The brightest of indoor spaces I measured was around 600 lux. To give you a gauge on this, your lounge room with all the lights on might average 150-200 lux. I took a set of readings throughout a suburban shopping mall in July (mid-winter). It was around 250 lux on average. I wanted to get a feel for what this translated to outdoors. To get a similar reading outside, I had to wait until around 20 minutes after sunset. In other words, the workers in this mall spent their entire day working in weak twilight. It doesn’t take much to think what effect this might have on people if you kept them in weak twilight for significant portions of time.
No matter where I took readings and no matter what the cloud cover was outside, it was always 100 times brighter outdoors as a minimum. The lowest reading I took for a workplace was in a café in Dunedin – 50 lux! Incredibly dim. Now this might be tolerable for a customer who is in there for 10-20 minutes while they drink their coffee, but what about the effects on the staff who are there all day? I took readings in the Dunedin Public Library. Dark. Very dark.
One interesting experiment I ran in Dunedin involved walking down the main street with the light meter. The shops there – being very old – have quite low overhangs. Given my newfound recognition and respect for light, I got the sense that even outdoors it was very dark. This was confirmed as I walked along the street, the light meter barely topping out over 250-300 lux, and often hovering under 100 lux. When there was a break in the buildings for a crossing, it would immediately jump up over 5000 lux (it was early in the morning in winter). Once safely across the road, the light intensity would drop back down again very quickly. Despite how dark it was, there were still plenty of people wearing sunglasses.
I went down to the University of Otago and while doing some writing in the main student library there, I decided to take some more readings. I was sat right next to the only windows in the library – south facing. Right by the windows it was 260 lux – still relatively dark. But step even a few meters back into the heart of the library, and the light levels drop away very quickly. Students spending their days here studying were sitting in under 100 lux of light. This becomes problematic when you start to piece together what we use our bright light exposure for.
As previously mentioned, there is much focus on melatonin as our primary ‘sleep hormone’ because of the association of low levels of melatonin and poor sleep architecture (such as delayed sleep onset or an inability to stay asleep for long). This often leads to people trying to boost melatonin levels via supplementation (either with melatonin directly, or its amino acid precursors) immediately prior to their intended sleep time, either as an everyday sleep aid, or when travelling between time zones and trying to stave off the worst of the associated jet lag. Melatonin, however, is most potent when produced endogenously as a downstream product of our daytime physiology and bright light exposure, specifically, its precursor, serotonin.
A neurotransmitter, serotonin is involved in regulating mood, appetite, memory and learning, and, important to this discussion here, sleep. Exposure to bright natural light (especially early in the morning) boosts serotonin production (in conjunction with the amino acid tryptophan and other vitamin and mineral co-factors consumed via a protein-rich breakfast), providing the raw materials for the melatonin required for our night-time physiology at the other end of the day. The converse is also true. The low melatonin leads to poor sleep train of thought is actually one of low morning light exposure plus a low protein intake (leading to low tryptophan and co-factor intake) leads to low serotonin production, which leads to low melatonin production, which leads to poor sleep. Already low melatonin can be further reduced by the already mentioned night-time blue-light exposure (light-induced melatonin suppression, LIMS).
The low melatonin story doesn’t end with sleep disruption. Indeed, melatonin performs a variety of functions in the human body. In addition to its regulatory role in our light-dark physiology, melatonin has antioxidative capacity, immunomodulatory potency, and appears to be protective against a variety of cancers, especially breast and prostate cancer. Melatonin receptors are also located in the ovaries, blood vessels, and intestinal tract. The binding of melatonin to its receptors on the pituitary gland and the ovaries appears to play a role in regulating the release of reproductive hormones in females. For example, the timing, length, and frequency of menstrual cycles in women are influenced by melatonin. Melatonin, in non-human mammals at least, also helps to signal the season and cue mating.
Serotonin, as a daytime neurohormone, is not the functional opposite to the night-time melatonin, however. Serotonin is not the day to melatonin’s night, as it were. That position is held by cortisol. Like serotonin, cortisol production is also stimulated by exposure to bright light such as sunlight and is the primary hormone responsible for waking us up and getting us going in the morning. In the context of typical health and wellbeing discussions, chronically elevated cortisol is often viewed negatively due to the association with it being a primary stress hormone. But we do require a strong, well-timed cortisol rhythm, where cortisol rises sharply from early in the morning (just prior to sunrise), peaks around mid-morning following bright sunlight exposure (while melatonin is low), then drops away over the remainder of the day and into the evening (as melatonin begins to rise once again).
Even dopamine, the neurotransmitter responsible for, among other things, motivating us to get out and get stuff done, is made in conjunction with bright light exposure. So, you can hopefully see the potential problems here. We spend a lot of time indoors. Too much time. It may also be dark when you go to work and dark when you come home. The very low levels of bright blue spectrum light we experience during the day is seeing our feel good and motivation biochemistry tank. With insufficient amounts of cortisol, serotonin, and dopamine in circulation, we’ll feel tired, fatigued, lethargic, apathetic, anxious, depressed… Sound familiar?
At night, the light intensity
outdoors is generally well under 10 lux and mostly under 1 lux, even with
bright moonlight. Meanwhile, indoors,
with all the LEDs burning bright (modern household lights, electronic device
screens, etc), it can be 200-300 lux in some rooms. During the day, this light intensity, relative
to the outdoors, is very dark. But now,
at night, 200 lux is 200 times brighter than 1 lux. Now this isn’t to say we should be sitting in
the dark, huddled around candles, but it illustrates the light inversion we
have in our modern world
– our days are relatively dark, while our nights are relatively bright. This is undeniably messing with our heads,
Recent research has suggested that spending too much time in relatively low light rooms could be changing the way our brains process information and impairing the growth of new neural connections. “Are Dim Lights Making Us Dimmer?”, read the headline of one report I reviewed. Our increasingly indoor lifestyles are also thought to be behind the global short-sightedness (myopia) epidemic, where up to half of young adults in the United States and Europe, and up to 90% of Asian teenagers are affected – over double the prevalence of 50 years ago. The strongest environmental risk factor for this large-scale loss of visual acuity across our populations of teenagers and young adults – the lack of bright natural light exposure associated with being indoors most of the day.
Many readers might be aware of, and perhaps even experienced, the phenomenon known commonly as the winter blues (Seasonal Affective Disorder – SAD). There seems a clear link between light exposure and a change in our mood, outlook, and wellbeing. A decline in serotonin levels with the reduced light exposure (length and intensity) and a concomitant increase in daytime melatonin levels, often in conjunction with dietary factors such as an insufficient specific amino acid intake, is at the heart of the winter blues we can often feel ourselves slip into. Living far from the equator appears to be a key risk factor for experiencing seasonal affective disorders, adding further support to the suggestion that changes in natural light exposures are fuelling this phenomenon.
The symptoms of winter-onset SAD include low energy levels, tiredness, cravings for foods high in carbohydrate (driving increases in body fat), sleeping problems, difficulty in concentrating, feelings of hopelessness or worthlessness, and suicide ideation. Summer individuals can experience a summer variant of seasonal affective disorder, but rather than depression, summer-onset SAD, driven by excessive light exposure (such as might be experienced during the “white nights” of high latitude countries in the summer months), is more likely to be characterized by anxiety and mania – easily over-stimulated, hyperactive, and displaying obsessive-compulsive type tendencies.
These extremes give us insight into the effects of light – too little, too much, poorly timed – on our mood and behaviour. While both winter- and summer-onset SAD may represent extremes, most of us function and experience variances in our moods along a continuum of light exposures. It’s hard not to see that rates of depression and anxiety are increasing while our light and dark exposure patterns are perhaps at their most extreme they’ve ever been in human history.
Like many of the common biological and evolutionary mismatches, the types of light exposures we experience now are relatively novel to us and our biochemistry. Electric lighting, on an evolutionary scale, is new enough. But as soon as you start considering urban life, work hours, LED lights, and our screen exposures, we are now considering something so very new to us and our delicately balanced brain chemistry. We have, in no uncertain terms, disconnected ourselves from the light and dark cycles of the planet. We cannot expect to do this without consequence.
It is at this point, as I wrap up, that we think about the practical solutions to dealing with this. The first thing for most people, as always, is awareness. I encourage people to install a light meter app on their phones (given most phones have cameras, they already have a light meter installed – a simple app, such as Lux Meter, will allow access to this tool). Once you have this, you can begin to map your world, as it were.
Take some readings in the places you hang out. At your desk. If it is too dark, see if you can get one closer to a window. At your coffee shop. If too dark, find another, or better still, sit outside. Look for ways to get your eyes out into the bright light as often as you practically can, from as early in the day as you practically can. Get away from buildings and walk more in the open if possible. Don’t wear sunglasses first thing in the morning – it will feel bright at first (possibly a sign that your melatonin levels are still too high), but you will quickly adjust. An important piece of research I found as part of this project, suggested that it is our daytime bright light exposure which is more important for setting our melatonin pulse at night than avoiding blue light at night, with the bright light exposure during the day mitigating most of the blue light at night effect. That said, still use the light meter to measure your light exposure at night and take steps to darken your night as much as possible.
There is a lot of focus on sleep, diet, and exercise in the wellness space – and for good reason. But a key fundamental we are all missing is our light exposure patterns and the impact these have on our ability to sleep, eat well, and be motivated and energised enough to exercise. We need to take back the light, pushing back against the insidious daylight robbery we’ve all been exposed to.
For more reading on this subject, I can thoroughly recommend the book Chasing the Sun by Linda Geddes, or this article by the same writer.
Thanks to Kate Scannell for her editorial help on this post.