HANNA AND BEN KING live in a large, modern house, with a fitted kitchen and bathroom, comfortable beds and hot running water. If it wasn’t for the horse-drawn buggy in the garage, and their unusual dress sense, you could be forgiven for thinking that you were visiting any American middle-class family home. Unless, that is, you visited after sunset.
As members of the Old Order Amish, Hanna and Ben follow the code of the ‘Ordnung’: a Pennsylvania-Dutch term for ‘order and discipline’, which outlines how they should conduct their lives. One of the things it forbids is connection to the electric grid. This isn’t because the Amish are opposed to electricity per se: they’re allowed to use batteries to power tools in their workshops, or for some practical household items such as Hanna’s sewing machine, which she uses to make traditional patchwork quilts and the family’s clothes – all in plain fabrics, and without buttons, which are deemed too ‘showy’. They even have a solar panel for recharging the batteries for these items, as well as a large, gas-powered fridge-freezer.
Amish households live off-grid because it’s an effective way of keeping the modern, ‘English’, world out. If you’re not connected to the grid then there’s no TV or internet; no electric gadgets like smartphones, which they worry would change and fragment their community, as well as leading to a less Godly existence.
It also means no electric lights at night. To see, Hanna’s family instead uses a single, large, stand-mounted propane gaslight, which they wheel between their enormous kitchen and living room. The lamp has a patterned glass lampshade, and a toy gibbon hanging off it, and it provides enough light for the family to cook and eat dinner by, as well as enabling them to read or stay up talking once its dark outside. In recent years, the family has also taken to carrying a battery-powered LED lantern with them when they go to the bathroom or enter other unlit parts of the house, including the bedroom – before that, they used a torch or oil lamp. Even so, once the sun goes down, most Amish households are far darker than the average American house.
There are other differences too. The Amish aren’t allowed to drive cars, because this might similarly fracture their community, so instead they walk; push themselves along on sturdy, adult-sized scooters; or, for longer journeys, hitch their horses to a buggy and set out on that. Many Amish men work outdoors – around half of men aged thirty-one to fifty are involved in farming – while their wives usually tend large vegetable patches. Also, in summer, the lack of air conditioning forces families outdoors to seek shade when they’re at home rather than sweltering indoors. As a result, the average Amish person spends far more time outside than their non-Amish contemporaries. If you want to know what life was like when we had a more direct relationship with the sun, it’s a good place to look.
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The early 1800s marked a turning point in our relationship with light. Before then, people experienced night in the old way, when the only source of indoor light besides firelight was the dim, flickering light of tallow candles or whale-oil lamps, which were unaffordable for many people and therefore used sparingly. People came up with innovative solutions to combat darkness and eke out these feeble sources of light: lace-makers would surround a burning candle with globes of water, to ‘magnify’ the light; miners working in Tyneside would even carry buckets of rotting fish down the mines, as these gave off a faint bioluminescent glow, which helped them to see.1 Even so, precise work was difficult in these conditions – especially during the winter months – and fire an ongoing hazard, not least in factories, where thousands of lamps were needed to provide enough light to see. Early candles and oil lamps were also smelly and sooty, and lamps needed regular maintenance to keep them working.
The introduction of gaslight was the first major change. The fuel burned by gaslights was a by-product from the production of coke, which was a popular fuel in homes and factories. It was made by heating coal in large ovens, which drew off the gassy fumes.
In 1802, the innovative engineering and manufacturing firm Boulton and Watt installed gas-lighting at their Soho foundry in Birmingham, where they made steam locomotives. These soon spread to other mills and factories, extending the day, and making shift work, which boosted productivity, a realistic proposition. The light produced by gas lamps was brighter than candles or oil, and considerably cheaper.
In 1807, the first gas street lights were erected in London’s Pall Mall; by 1820, there were 40,000 of them in the capital alone, not to mention several hundred miles of underground gas pipes, fifty gasometers – large containers used to store gas – and an army of lamplighters employed to tend the street lights, which they lit using an oil lamp attached to a long pole.
As the popularity of gaslights grew, the evenings were transformed – at least in the cities, which had gas mains. The word ‘nightlife’ dates from 1852: in the brightened evenings, cafés and theatres flourished, and window-shopping became a popular evening pastime for the rising middle classes. Gaslights also made it safer to wander the streets at night and were credited with reducing crime.
As Robert Louis Stevenson wrote in his 1878 essay ‘A Plea for Gas Lamps’:
When gas first spread along a city, mapping it forth about evenfall for the eye of observant birds, a new age had begun for sociality and corporate pleasure-seeking … Mankind and its supper parties were no longer at the mercy of a few miles of sea-fog; sundown no longer emptied the promenade; and the day was lengthened out to every man’s fancy. The city-folk had stars of their own; biddable, domesticated stars.2
Some of these gaslights can still be found in isolated pockets of large cities, such as St James’s Park in London and Beacon Hill in Boston, Massachusetts. The warm, flickering glow they give off is quite unlike the fierce, blue-white light of modern LED street lights.
Until the invention of paraffin (kerosene) in the 1850s, provincial towns, villages and farms lagged behind in the dark. The demand for paraffin, distilled from petroleum, helped usher in the age of oil. A large paraffin lamp burned as bright as five to fourteen candles, and these soon became a focal point for provincial families during the autumn and winter evenings. No longer did people have to spend their evenings in darkness; these cheaper, brighter lights made it easier to stay up later reading, sewing or socialising. However, this light was feeble compared to what was about to spark up.
The first record of electricity can be traced back to ancient Greece, where, in around 585 BC, the philosopher Thales of Miletus discovered that if he rubbed amber with a piece of fur, the amber would start to attract lightweight objects such as feathers to itself. Primitive batteries, consisting of a clay jar filled with an acidic substance such as vinegar or wine, and a copper cylinder encasing an iron rod, have also been discovered near Baghdad and have been dated to around 200 BC, although their purpose remains a mystery; archaeologists have suggested that they may have been used in electroplating, acupuncture or hooked up to religious icons to deliver a small shock and a flash of light, if touched.
It wasn’t until the turn of the nineteenth century that this mysterious force was harnessed to generate light. In 1802, Sir Humphry Davy discovered that passing an electric current through a platinum filament caused it to glow momentarily. Then, in 1809, he demonstrated the first carbon arc lamp, which worked by passing an electric current between two rods of charcoal. Pulled apart, these charcoal rods created an arc of brilliant blue-white light, far brighter than any gaslight. The rods also glowed incandescently, generating an illuminance of their own.
The challenge was to create a more compact and reliable battery, as well as longer-lasting conductor rods, as the charcoal sticks quickly burned away. The breakthrough came in the 1820s, when Davy’s assistant, Michael Faraday, discovered that passing an electric current around an iron bar could turn it into a magnet, and that moving a magnet around a coil of wire could create an electric current. The electric generator was born.
Not everyone was a fan of these carbon arc lamps, however. In his 1878 essay, Stevenson continued:
In Paris … a new sort of urban star now shines out nightly, horrible, unearthly, obnoxious to the human eye; a lamp for a nightmare! Such a light as this should shine only on murders and public crime, or along the corridors of lunatic asylums, a horror to heighten horror. To look at it only once is to fall in love with gas, which gives a warm domestic radiance fit to eat by.3
Arc lamps were considered too intense for lighting the home. However, ever since Davy demonstrated the ability of platinum filaments to glow when an electric current passed through them, people had been trying to come up with a way of sustaining this alternative, ‘incandescent’, source of light. The challenge wasn’t only technical: to be practical for general household use, electric lighting needed to be cost effective and easy to use.
In 1878, Thomas Edison picked up the mantle. It was Edison who said that ‘genius is 1 per cent inspiration and 99 per cent perspiration’. He also, famously, boasted about needing no more than three hours of sleep per night – although he was often spotted catnapping. As one associate put it: ‘His genius for sleep equalled his genius for invention. He could go to sleep anywhere, any time, on anything.’4
No wonder, if he was only getting three hours of sleep during the night. Today, the US National Sleep Foundation advises that adults aged eighteen to sixty-four need to get seven to nine hours of sleep per night (seven to eight hours for those over sixty-five), and that individuals who routinely sleep less than six hours (five hours for those over sixty-five) risk compromising their health and well-being.
It seems appropriate, then, that Edison’s most famous invention has been so pivotal in undermining our relationship with the natural light-dark cycle, enabling us to work and socialise around the clock. In 1879, Edison successfully tested the first practical incandescent light bulb, and was ultimately responsible for bringing cheap electric lighting to the masses.
Edison didn’t achieve this feat alone: his ‘invention factory’ at Menlo Park, near New York, was crammed with blacksmiths, electricians and mechanics. Also employed on his staff was a mathematician and a glass-blower. Consisting of a coiled filament of carbonised cotton thread surrounded by an evacuated glass bulb, Edison’s light bulbs finally allowed households to generate light at the flick of a switch, without the need for an open flame. They were safe enough that a child could be left unsupervised in a lighted room, and they were cheaper than either paraffin lighting or gas.
In the 140 years since Edison’s invention, electric lighting has spread far and wide, transforming the way we live our lives. And it continues to grow ever brighter: a recent study of satellite images revealed that the earth’s artificially lit outdoor area is currently increasing by more than 2 per cent a year.
Viewed from space, the spidery networks and nebulous clusters of light could be a mirror of the heavens, but from the ground in these brightly lit areas the real stars are vanishing from sight. Today, two thirds of Europeans and 80 per cent of Americans are unable to see the Milky Way from their homes.
‘Imagine if we woke one day and were unable to see the green fields and hills of Wales … the forests of the Amazon, the mountains of Nepal, or the great rivers of the world,’ says British professor of cosmology and culture, Nicholas Campion. ‘But that is what we have done, and are doing, with the sky, impoverishing our lives in the process.’5
Electric lighting has undoubtedly brought many benefits, but it comes at a cost. The loss of our night skies is one of them. The quality of our sleep may be another.
Donald Pettit sits in the cupola of the International Space Station, his camera lens poised for sundown. As he flies over earth’s dark oceans, he records the brilliant flashes of thunderstorms and the undulating beauty of the aurora borealis. But the real light show begins when the continents roll into view. The splats and trails of light glow like a fluorescent Jackson Pollock canvas: orange speckles emanating from sodium vapour lights; blue-green blotches from mercury lights; and whitish-blue webs from newer LEDs.
Pettit has spent more than a year on board the International Space Station, snapping thousands upon thousands of photos of our planet.6 Such shots are now being stitched together by the Cities at Night project,7 which aims to document the extent of light pollution and how it’s changing due to the growing popularity of LED street lights.
Urban lights scatter photons in unwanted directions, including upwards into space. This scattered light obscures drivers’ vision and wreaks havoc on wildlife. Mesmerised by this apparent daylight in the night sky, insects’ life cycles are disrupted, birds’ migration is thrown off course, and trees cling to their leaves for longer in the autumn – potentially shortening their lives.8 Even the reproduction of flowering plants is affected by these artificial suns; by disrupting the behaviour of pollinating insects, their daily appointments with flowers that open and close at specific times are missed.9
Artificial light also takes a toll on our sleep. A 2016 study found that people living in areas with elevated levels of light pollution tend to go to bed and wake up later than those living in darker areas. They also sleep less, are more tired during the daytime, and are less satisfied with the quality of their slumber.10
For centuries, sleep was regarded as a passive and largely dispensable state, and it is an attitude that continues today: ‘Don’t sleep any more than you have to,’ advised Donald Trump in his 2005 book, Think Like a Billionaire.11 He claims to sleep for just three to four hours per night.
Among sleep scientists, though, there’s a growing consensus that getting enough sleep is fundamental to our ability to learn, find solutions to problems and regulate our emotions – as well as reading those of other people. Indeed, the way we sleep may underpin our success as a species.12 Our emotional proficiency is what enables us to cooperate and build flourishing societies, while our creativity, together with our ability to learn and assimilate knowledge, underpins our technological achievements. All these things hinge upon sleep.
Humans sleep in 90-minute cycles, which are further subdivided into periods of non-REM (NREM) and REM sleep. The first half of the night is dominated by NREM sleep (which is itself divided into light NREM and deep NREM sleep), while during the second half of the night REM sleep predominates – although both types of sleep occur during every 90-minute cycle.
The precise purpose of sleep is still a subject of intense study, but one key function of NREM sleep seems to be weeding out unnecessary connections between brain cells, while REM sleep is believed to strengthen those connections.
In his book, Why We Sleep, the neuroscientist Matthew Walker likens the interplay between these sleep states to creating a sculpture out of clay: you start out with an unwieldy lump of raw material, equivalent to the mass of old and new memories that the brain has to work with each night. During the first half of the night, NREM sleep excavates and removes large amounts of superfluous material, while short bouts of REM sleep smooth and mould the basic shape. Then, during the second half of the night, REM sleep works on strengthening and defining these basic features, with just a small amount of input from NREM sleep.
It is through this process that our memories are sculpted and archived. Sleep – specifically, the deep NREM sleep that predominates during the first half of the night – helps to consolidate newly acquired memories, so, if you’re cramming for an exam, you need this kind of sleep to make those facts stick.
Meanwhile, short and intense bursts of light NREM sleep, called spindles – which are prolific during the second half of the night, where they punctuate long bouts of REM sleep – seem to be involved in transferring recently acquired memories to longer-term storage. This frees up our capacity to learn and manipulate new knowledge the next day. As we age, we experience fewer of these spindles, which could help explain why our memory for new things tends to deteriorate. It’s not only facts that are archived during sleep, but physical skills, such as how to juggle more balls or perform a stunt on your bike. Getting enough sleep is therefore extremely important for athletes – a subject that we will return to in chapter 9.
What about REM sleep? This is the sleep state associated with dreaming; animal studies suggest it may also be when we replay memories accrued during the day. One function of REM sleep appears to be fine-tuning our emotions. If we don’t get enough of it, we become less adept at reading other people’s facial expressions and body language, so our ability to empathise and communicate suffers. We also become less capable of regulating our own emotions. When researchers selectively deprived healthy young adults of REM sleep, but allowed them plenty of NREM sleep, within three days some of them were displaying signs of mental illness – seeing and hearing things that weren’t there. They also became paranoid and anxious. This is worrying in the context of owlish teenagers cutting short their sleep because they have to get up early for school (see chapter 10): it is their REM sleep that will suffer the most.
REM sleep is also responsible for cross-referencing newly acquired memories with the back catalogue of older stored memories in your brain. It is during REM sleep that creative insights and abstract connections tend to be made, which is why sleeping on a problem often provides a solution.
We need all these distinct types of sleep if we’re to function as intelligent and emotionally competent individuals. And while it’s true that some individuals may need less sleep than others, we’re kidding ourselves if we think that routinely getting less than six hours of sleep is okay. When we restrict our sleep, it tends to be REM sleep that suffers disproportionately. But fractured sleep – where we sleep lightly and wake frequently – also erodes the NREM sleep that we get more of at the beginning of the night.
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In recognition of the impact that light pollution might be having on our sleep, the American Medical Association recently issued guidance on LED street lights, which are increasingly replacing older mercury- or sodium-based ones. It advised communities against fitting standard blue-white LED street lights – estimated to have a five times greater impact on people’s circadian system than older types of street lights – opting for warmer-coloured ones instead; they also suggested that street lights should ideally be dimmable and installed with shields around them to reduce the amount of light reflected upwards into people’s bedrooms.
Some city authorities are starting to take notice. New York and Montreal have altered their plans to install standard blue-white street lights, adopting warmer shades instead. In St Paul, Minnesota, tuneable street lights are even being tested that could allow city authorities to adjust their colour or intensity based on the time of day, weather or traffic conditions.
Meanwhile, in towns like Moffat, a solid-looking, former staging post on the road from England to Edinburgh, the street lights have been fitted with shades to direct their glare downwards. Such measures have earned Moffat the title of Europe’s first ‘dark sky town’.
I visited Moffat to see how these new lights were working out. As I walked through the town, on a frosty October night, the street lights looked like pin pricks of light, rather than glaring beacons, and, off the main streets, it became dark very quickly. On clear nights like these (which are admittedly rare in southern Scotland), the Milky Way casts a magnificent streak across the inky sky.
Such measures are welcome, but they don’t deal with the more personal issue of how we choose to light our indoor spaces. Before Edison’s invention, the brightest lights in our homes were gaslights, like the ones used by Amish families, and before that, oil lamps and candles. So what impact is our indoor lighting having on our sleep?
* * *
I arrived at Hanna and Ben’s home on the Friday before Memorial Day weekend. I was accompanied by Sonia, another ‘English’ girl (the Amish refer to all outsiders as ‘English’, although Sonia is American). The daughter of a psychiatry professor who runs medical studies on this community, Sonia had been handed the keys to her dad’s enormous pick-up truck in order to drive me there – her first independent road trip, having just completed high school. We picked Hanna up from an indoor farmers’ market, where she sells cheese, along the way.
Although they’re not allowed to drive, the Amish can accept lifts. Hanna was pleased to see the truck because it would make the weekend more productive. She pulled out a schedule of yard sales she was hoping to attend the following morning. ‘Do you want to come with me?’
Going yard-sale shopping, Hanna warned, would mean an early start – at least as we might regard it: 4.45 a.m. is the time she gets up every day, waking without an alarm clock, having gone to bed at around 9 p.m. the night before.
Among the Amish, Hanna is by no means unusual in rising before dawn. On average, Amish people go to bed and wake up approximately two hours earlier than Americans with free access to electricity – meaning that their waking period is more closely aligned with the solar day.
After a quick breakfast of fried egg sandwiches, we’re out of the house and pulling into the parking lot of our first yard sale at 5.30 a.m., where several black, horse-drawn buggies are also hitched. Already, a man with a chin-curtain beard, and the distinctive Amish uniform of straw hat, plain shirt and braces, is firing up a barbecue, and the smell of smoke and grilled chicken intermingles with the sweet smell of desserts. Women wearing ankle-skimming dresses, with black aprons and white head-coverings topping their centre-parted, neatly pinned hair, are rummaging through tables of second-hand clothes and bric-a-brac. The Amish typically have large families – Hanna is one of six, but ten is not uncommon – so there are lots of toys, baby clothes, pushchairs and tricycles. Men’s second-hand, black, wide-brimmed hats are $5 a pop and there’s a lot of Tupperware for sale.
To some extent, these early starts may be cultural: certainly, there are Amish people who would prefer to sleep later. One of them is Katie Beiler, who runs a plastic-food-storage empire. Katie is up at 4.30 a.m. each day because her husband leaves the house at 5 a.m. but, given the choice, she’d remain in bed until 6.30 a.m. ‘It’s not that I can’t get up early, it’s just that I love to sleep in,’ she says.
Half-past six may not sound like much of a lie-in, but it’s all relative. According to recent studies, more than three quarters of Old Order Amish people are early chronotypes or ‘larks’, compared to just 10 to 15 per cent of the general population.13
This pattern of going to bed early and rising shortly before dawn has a long tradition. Buddhist monks are said to have held their hands up to the morning sun, and if they could see their veins, it was time to get up. The same pattern is found among other communities who live without electric light. For instance, a study which examined sleep among members of the Hadza in Tanzania, the San tribe in Namibia, and the Tsimane in Bolivia, found that they too stay up for several hours after sunset, but go to bed relatively early and wake shortly before dawn, sleeping for an average 7.7 hours per night.14
Such studies are of interest because they give some clues about how our altered relationship with light might be affecting our sleep. Not only do people living in some pre-industrial societies go to sleep earlier than us, they also seem to sleep better. Between 10 and 30 per cent of people in Western countries experience chronic insomnia, whereas just 1.5 per cent of Hadza and 2.5 per cent of San participants interviewed said that they regularly had problems falling or staying asleep. Neither group has a word for ‘insomnia’ in their language.
Sonia’s father, Teodor Postolache, and his colleagues have been studying illuminance levels in Old Order Amish households. We measure illuminance in lux, which refers to the amount of light striking a surface. The full moon on a clear night is 0.1 to 0.3 lux, or up to 1 lux in the tropics – about the same as candlelight. In most Amish homes, the average illuminance during the evening is around 10 lux, which is at least three to five times lower than evening light levels in electrified homes.
The researchers have also discovered that daytime light exposure is much higher among the Amish than for most of us in Western countries, where we spend approximately 90 per cent of our time indoors.
This is important because the amplitude of circadian rhythms – the difference between the peaks and troughs of the various rhythms in our bodies – is reduced if we are exposed to more constant light conditions between day and night. Such ‘flattening’ of the circadian rhythm has been associated with poorer sleep, and is observed in many illnesses, from depression to dementia (see chapter 8, ‘Light Cure’).
During the summer, Amish people are exposed to an average daytime illuminance of 4,000 lux, whereas the average Brit is exposed to 587 lux. During winter, the Amish experience lower levels of daytime light – around 1,500 lux but for us indoor-dwelling Brits, the average daytime illuminance is just 210 lux: in other words, our waking hours are approximately seven times gloomier than those of the Amish.
Yet it doesn’t necessarily feel gloomy to us because the human visual system, remarkable as it is, is a relatively poor judge of illuminance. Your workplace lighting may seem bright enough, but that’s because your visual system has adapted to its surroundings, just as it does when you turn off your bedroom light at night and initially can’t see anything but then soon make out most objects clearly.
The illuminance in a typical office is between 100 and 300 lux during the daytime, whereas even on the gloomiest, most overcast winter’s day it is at least ten times brighter outside. During the summer, when the sun is higher in the sky and there are no clouds, it can reach 100,000 lux.
In the West, we spend our daytimes in the equivalent of twilight, and then keep the lights switched on well after sunset. Some of us even sleep with a night-light on, while city dwellers often have light pollution from street lights to contend with. It’s a far cry from the clearly defined daily cycle of light and dark that humans evolved under.
Being exposed to higher levels of light at night does several things: it delays the timing of our body clock and suppresses melatonin, which means that we feel tired later; when our alarm clocks wake us up the next morning, we are still in sleep mode; and overall we get less sleep. It also means that the daily nadir in mood and alertness, which is biologically programmed to occur shortly before dawn when we’re asleep, occurs when we’re awake instead.
However, the concern around light at night doesn’t centre only around the circadian clock and melatonin suppression. Those same light-responsive cells in the eye that synchronise our circadian rhythms also project to areas of the brain that control alertness. Bright light puts the brain into a more active state – it literally wakes us up. One recent study found that exposure to an hour of low intensity blue light boosted people’s reaction times (a measure of alertness) by more than if they had consumed the equivalent of two cups of coffee. When caffeine and light were given together, people’s reactions were even faster. This could be good news if we’re exposed to bright light during the daytime, but at night it could be further undermining our ability to sleep.
This may be one reason why exposure to electronic screens in the run-up to bed is bad for us. Another study found that, compared with reading a print book, using an e-reader prolonged the amount of time it took participants to fall asleep, reduced the amount of REM sleep they experienced and left them feeling more tired the next morning.
Adjusting the light settings on your phone or tablet – or installing an app that automatically filters out blue light after sunset – can help. Even so, most sleep researchers advocate ditching screens altogether in the 30 minutes before bed – and ideally for several hours beforehand – because even relatively dim light sources held close to the eyes can inhibit melatonin and may therefore affect sleep.
Bright light affects our bodies in other ways too: it increases our heart rate and core body temperature. Usually these things are at their lowest during the night-time, and although the changes brought about by light exposure are relatively small and short-lived, the long-term consequences of repeatedly raising them at night are unknown.
* * *
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.15 ‘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 hangover could contribute towards feelings of grogginess in the morning.
He recently repeated the experiment in winter.16 This time, he found that participants went to sleep some 2.5 hours earlier after a week of outdoor living, compared to normal, yet they still woke up at roughly the same time, which meant that they slept for around 2.3 hours longer. ‘We think it’s because people were going back to their tents earlier to get warm, so they were giving themselves a longer opportunity to sleep,’ says Wright, who accompanied them on the winter trip: ‘One of the nights it was so cold that we didn’t even have a campfire.’
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.
* * *
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.
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.’
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 maximise 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 midwinter. 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 socialising 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 socialising – and to make dinner preparation a little easier, we eventually installed a dimmable colour-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 cosier, 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 (Waldschattenspiel), 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 realised 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.17 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 1 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 Figueiro 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 metre or so away from them, the daylight largely disappeared. Office partitions and people pulling the blinds further reduced its penetration into the office.
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.18
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.19
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.20 ‘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.21 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.22
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There’s another reason why Amish are an interesting population to study from the perspective of light. Lancaster County, where Hanna and Ben King live, is on roughly the same latitude as New York, Madrid and Beijing. Yet, while the prevalence of seasonal affective disorder (SAD) in New York is 4.7 per cent, the Amish have the lowest prevalence yet recorded in any Caucasian population.23
They also have very low rates of general depression. In part, this could be because of their culture of ‘Gelassenheit’, or one’s ‘submission to a higher power’. Acknowledging that you’re feeling low could be interpreted as ingratitude for what God has provided, or a preoccupation with one’s self.
However, it could also be related to their relationship with light. Because their body clocks are more closely aligned with the solar day, it’s likely that biological night has ended for most Amish people by the time they wake up – even though they wake earlier, their master clocks have already issued the orders that cause our mood and alertness to increase during the day. And, because they walk or scoot to work and spend more time outdoors generally, any residual melatonin in their systems that could be making them feel sleepy is suppressed by the bright light.
There could be another reason too. Those light-responsive eye cells that speak to the brain’s master clock and the alertness centres of the brain plug into yet other regions that regulate mood. Early morning exposure to bright light is a proven strategy for treating SAD – and there’s mounting evidence that it is effective in general depression as well (see chapter 8). Similarly, in the GSA study, those workers who were exposed to a high circadian stimulus during the morning also scored lower on a self-rated scale of depression.
In other words, their early morning starts, combined with walking or scooting to work, and spending a greater proportion of their days outdoors, could be furnishing the Amish with a natural antidepressant.
This also fits with the results of my own experiment. Immediately after waking and before going to bed each night, I filled out a questionnaire to assess how positive and negative I was feeling. This revealed that my early morning mood was significantly more positive during the intervention weeks compared to normal ones. The early morning grogginess was gone: I felt more energetic and uplifted, and ready to start the day. Because of this experience, I’m a convert to outdoor exercise, and I’ve even come to look forward to certain aspects of winter, particularly the bright, frosty days and the spectacular sunsets.
Taken together, such results emphasise the importance of daylight. They also have significant practical implications. Although few of us would be prepared to spend our evenings in candlelight on a permanent basis, spending time outdoors during the daytime may be something more of us can work into our lives.