By Linda Geddes
Ever since the discovery that light—and particularly blue light—can suppress melatonin and alter the timing of our circadian clocks, evidence has been building that exposure to even low levels of light in the evening and during the early part of the night may be affecting the quality of our sleep. Yet light isn’t always malign: there is growing evidence to suggest that exposing oneself to bright light during the daytime can help to negate some of the detrimental effects of light at night—as well as improving our mood and alertness more directly.
So what would happen if we followed the Amish’s example and reverted to a more traditional relationship with light?
Kenneth Wright, at the University of Boulder in Colorado, has long been fascinated by how our modern light environment might be affecting our internal timing. In 2013, he sent eight people camping in the Rocky Mountains for one week during the summer and measured how this affected their sleep. “Camping is an obvious way of removing ourselves from this modern lighting environment and just getting access to natural light,” he says.
Before the trip, the average bedtime of the participants was 12.30 a.m., and their wake time was 8 a.m., but both had shifted approximately 1.2 hours earlier by the end of the trip. This was even true of the night owls, who began to look decidedly larkish after a week outdoors. They weren’t getting significantly more sleep—at least when the experiment was conducted in summer—but their sleep was more in line with the natural light-dark cycle outdoors.
The participants also started releasing melatonin some two hours earlier once they were removed from artificial evening light, and, by the time they woke up, melatonin production had switched off, whereas at home it continued for several hours after waking. Wright suspects that this melatonin hang over could contribute towards feelings of grogginess in the morning.
However, the Amish too appear to sleep for around an hour longer during winter compared to summer. It is still unclear why these seasonal differences in sleep occur—or if it matters if we override them, as we do in modern society.
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Inspired by Wright’s studies and observations of more traditional societies, I decided to go cold turkey on artificial light at night myself, and to spend more time outdoors during the daytime. I was interested to see if this would translate into any wider benefits to my health and well-being. We may not need to completely forgo electric lighting in the evenings in order to reap the benefits of improved sleep and daytime performance.
Working with the sleep researchers Derk-Jan Dijk and Nayantara Santhi at the University of Surrey, we designed a protocol to measure the effect of these changes in light exposure on my mood, alertness and sleep. It would be a bit like Wright’s camping experiment except that I’d be doing it while trying to juggle an office job and busy family life in central Bristol.
Before the experiment, my sleep routine was fairly typical for a British person: I’d go to bed at around 11.30 p.m. or midnight and be reliably woken up at 7.30 a.m. each morning by my children, who are like human alarm clocks. Even though I slept soundly compared to many of my countrymen—the average British adult goes to bed at 11.15 p.m. but gets just six hours and 35 minutes sleep per night—I often felt groggy in the mornings and would have liked to sleep for longer.
Also, like three quarters of British adults, I had the unfortunate habit of routinely checking my smartphone just before bed, blasting myself with a dose of blue light, which-as we’ve already learned -inhibits melatonin and pushes the master clock later, potentially making it harder to get to sleep.
Larger studies in the more controlled environment of a sleep laboratory had hinted that by changing my light exposure patterns I might feel sleepier earlier and fresher in the morning—but this didn’t necessarily mean that these benefits would translate into real life: “We’ve done a lot of experiments where we’ve given a dose of light and seen that it shifts the clock,” says chronobiologist Marijke Gordijn at the University of Groningen in The Netherlands. “If we want to apply those findings to help people, we need to know that it will have the same effect when the environment is more variable.” Exposure to bright, morning light was particularly powerful.
Despite the lure of better sleep and happiness, persuading my family to embark on such an experiment took some effort. My husband rolled his eyes, and my six-year-old daughter was only brought round by the promise that it would be just like camping—and by the added bribe of marshmallows.
During the first week, I’d do everything I possibly could to maximize daylight exposure: moving my desk next to a large, south-facing window, loitering in the park after school drop-off, eating lunch outdoors, and substituting indoor exercise with an outdoor equivalent. Another week, we turned the lights off after 6 p.m., even though this meant cooking in the dark—I embarked on the experiment in mid winter. Computers and smartphones were banned in the evenings, unless absolutely necessary, and then only if they were in “night mode” in order to reduce the amount of blue light they emitted. During a third week, I combined both sets of interventions—keeping things bright in the day and dark at night.
To track my responses, I wore a device on my wrist that captured information about light exposure, activity and sleep. I filled in daily diaries and questionnaires to record my mood and alertness, and I did a battery of online tests to measure my reaction speed, attention and memory. Finally, on the last night of each week, I sat in the dark, spitting into a tube in order to work out when I started releasing melatonin—that marker of internal time. Such is the glamorous life of a scientist.
Cooking by candlelight was a daily challenge. On New Year’s Eve, we hosted a candlelit dinner party and managed to undercook our friends’ burgers; chopping carrots was an outright hazard. I began preparing meals earlier, which ate into my work time, and panic-checking my pockets to ensure that I hadn’t misplaced the box of matches. My pledge to avoid artificial light also made socializing difficult. Despite the challenges, I did significantly reduce the amount of light I was exposed to after sunset—and this did throw up some interesting findings. During my “dark weeks,” the average illuminance in my home between 6 p.m. and midnight was 0.5 lux—which is only a little brighter than moonlight. Candlelight was perfectly adequate for reading, writing Christmas cards and socializing—and to make dinner preparation a little easier, we eventually installed a dimmable color-changing light bulb near the cooker.
And, once we adapted, we found that living without artificial light was a pleasure. The candles made the dark winter evenings feel cozier, and conversation seemed to flow more freely. Rather than habitually switching on the television, we turned to more sociable activities, such as board games. Seeing our enthusiasm for this new way of living, friends started dropping by in the evenings to experience it for themselves; they commented on how relaxed they felt in the warm dim light. On New Year’s Eve, rather than raucous merry-making, we sat in the dark and played a German board game called Shadows in the Woods (Waldschatten spiel), in which participants take on the role of dwarves who must hide in the shadows of 3D cardboard trees to avoid being caught in the glare of a malevolent tea light. Another bonus was that our children seemed to settle more easily in the evenings (although we didn’t quantify this).
Spending more time outdoors in daylight provided another revelation. Initially, it was hard to overcome the belief that, because it was winter, it would be cold and miserable outside, but I was reminded of something a Swedish friend used to say: there’s no such thing as bad weather, only inappropriate clothing. And I soon realized that it’s rarely as bad outside as it may look. Indeed, the more I did it, the more I came to regard getting outdoors in winter as a treat, rather than a chore.
My attitude to winter began to change. I registered the beauty of hoar frost on rosehips, and the tranquillity of an empty park on a bright December morning, with its long shadows and the sunlight glittering off the ice crystals on the grass.
On one such morning, I took a cup of tea to the park, sat on a chilly bench and made my to-do list for the day. When I pulled out my light meter, it wasn’t far off the sort of reading you’d expect on a cloudless day in summer. Back indoors, I took another reading from the middle of my office—it was 600 times dimmer.
British employers have a duty to provide lighting that’s safe and doesn’t pose a health risk, but currently this doesn’t take the potential impact on our circadian systems into account. The UK’s Health and Safety Executive recommends an average illuminance of 200 lux in most offices, while for work requiring limited perception of detail, including most factories, it is just 100 lux. A recent study found that American adults spend more than half of their waking hours in light even dimmer than this, and only around a tenth of their time in the equivalent of outdoor light.
But did doing any of this have any measurable impact on my sleep or mental performance? There was a general trend towards earlier bedtimes. Although, because it was December, social commitments meant that I sometimes ignored my sleepiness and stayed up later anyway: living by the body clock isn’t always as straightforward as it is in a lab study. Possibly because of this, the overall amount of sleep I got each night didn’t vary significantly between normal and intervention weeks.
Even so, tests showed that—like the participants in Wright’s camping study—my body started releasing the darkness hormone, melatonin, some 1.5 to two hours earlier when I cut out artificial light or got more daylight. I also felt more tired in the run-up to bed.
When I correlated my sleep measurements with the amount of light I was exposed to during the daytime, another interesting pattern emerged. On the brightest days, I went to bed earlier. And for every 100 lux increase in my average daylight exposure, I experienced an increase in sleep efficiency of almost r per cent and got an extra 10 minutes of sleep.
This pattern has also been seen in larger, better controlled studies than my own. The General Services Administration is the largest landlord in the United States. Its bosses wanted to establish whether designing more daylight into its buildings made any difference to the health of those working inside them. Working with Mariana Figueira at the Lighting Research Center in Troy, New York, they assessed the sleep and mood of office workers in four of their buildings—three of which had been designed with daylight in mind, one of which hadn’t.
The data was initially disheartening. Despite efforts to boost daylight, many GSA workers still weren’t getting very much of it: although it was bright close to the windows, once you travelled a meter or so away from them, the daylight largely disappeared. Office partitions and people pulling the blinds further reduced its penetration into the office. “When we’re talking about the problem of kids looking at iPads in the evening, it’s having detrimental effects if they’re spending their daytimes in biological darkness.”
Yet when Figueiro compared workers receiving a large amount of light that was bright or blue enough to activate the circadian system during the daytime—a high circadian stimulus—with those receiving a low stimulus, she found that the former group took less time to fall asleep at night and slept for longer. Exposure to bright, morning light was particularly powerful: those exposed to it between 8 a.m. and noon took an average of 18 minutes to fall asleep at night, compared to 45 minutes in the low light exposure group; they also slept for around 20 minutes longer and experienced fewer sleep disturbances. These associations were stronger during winter, when people may have had less opportunity to receive natural light during their journey to work.
Meanwhile, Gordijn has recently assessed the effect of daylight on sleep structure in a highly controlled laboratory setting and found that it was associated with greater amounts of deep sleep—which you need to feel refreshed in the morning—and less fragmented sleep.
Our sleep isn’t the only thing that’s affected by daylight exposure. During all three intervention weeks I felt more alert upon waking than normal—but particularly during the two weeks when I was exposed to more daylight.
A recent German study suggested that exposure to bright light in the morning boosted people’s reaction speeds and maintained them at a higher level throughout the day—even after the bright light had been switched off. It also prevented their body clocks from shifting later when they were exposed to blue light before bed.
This is good news because it suggests that we may not need to completely forgo electric lighting in the evenings in order to reap the benefits of improved sleep and daytime performance. Mounting evidence suggests that just by spending more of our daytimes outdoors or exposed to brighter indoor lighting we might achieve the same result. “When we’re talking about the problem of kids looking at iPads in the evening, it’s having detrimental effects if they’re spending their daytimes in biological darkness,” says Dieter Kunz, who carried out this research. “But if they’re in bright light during the day it may not matter.”
It may even improve their school performance, as teachers at a school in Hamburg, Germany, discovered, when they participated in a study on the impact of different kinds of lighting in the classroom. When the teachers switched on lights that mimicked daylight in both colour and intensity, their pupils made fewer errors in a concentration test, and their reading speed increased by 35 per cent. A study in office workers similarly revealed that exposure to blue-enriched lighting during daytime hours boosted people’s subjective alertness, concentration, work performance and mood; they also reported better quality sleep.
Source: lithub.com