Light Extracts

As more of us move into light-polluted cities, spending our days in dim offices our evenings watching brightly lit screens, we are in danger of losing something vital: our connection to the star that gave vis life. It's a loss that could have far-reaching consequences re only just beginning to grasp.

Introduction

At the largest of these - the Ivanpah Solar Plant, 45 miles south-west of Las Vegas - a glittering sea of sun-tracking mirrors captures and focuses sunlight onto three boiler-topped towers, which drive turbines that supply electricity to hundreds of thousands of homes.

Across the ages, in civilisations separated by thousands of miles of land or ocean, people have revered the sun as both a creator and a destroyer-a relationship that continues to this day.

The artificial light also confuses the navigation ystems of insects, luring them to their deaths: the concen- rated swarms provide a buffet for bats, which are in turn easted upon by swooping owls

Elsewhere in Vegas, realising the power it wields over our minds and spirits, resort owners have deliberately ban- ished the sun from their casino floors. The 24-hour cycle of and darkness is crucial to our internal sense of time; if here are no windows, it's easier for gamblers to lose track of it and stay for hours longer than they mean to - particu- larly if artificial light is deployed to wake them up- Some casinos even go so far as forbidding dealers from wearing a ratch, so that if anyone asks the time, they can't say.

Blue-white light simulates daylight and makes people feel more alert,

Meanwhile, red light can raise our level of physiological arousal: a study has shown that people gamble more money, place more bets and choose riskier options under red light, compared to blue. that red light with fast music, another study showed, and people will bet faster on roulette.

Finally? I found myself surrounded by mock-Greco- architecture in the labyrinthine mall of Caesar's 'alace, glimpsing what appeared to be daylight up ahead. excitement was quickly deflated as I drew closer and up: above me soared an impressive - yet completely artificial - sky. As I slumped, defeated, next to a replica of s Trevi Fountain, it struck me just how perverted our slationship with natural light has become.

And as the sun's light penetrated our eyes, it changed the chemistry of our brains, tweaking pathways that control our internal sense of time. So the sun brought order to our ancestors' biochemical reactions and behaviours and, as they looked up at the sun and at the pinpricks of light that decorated the heavens, they found that it also brought spin- tual order to their lives. worshippers of Britain and Ireland to the Inca who believed they were descended from the sun god Inti. Our histories, religions and mythologies are packed with solar symbolism - whether it's the Greek god Helios pulling the sun across sky in his chariot; the ochre-hued Sun Woman in the lythology of the Aboriginal people of northern Australia, carrying her torch across the sky; or the significance of light rebirth in Christianity. makes sense, because from humanity's very innings, the sun has governed both our bodies and our rperience of the world. To our ancestors, the daily rising setting of the sun, and the seasonal fluctuations in light and food must have seemed extraordinary, not mention life-changing.

Particularly in a place like northern Europe, you will have watched the sun moving a little further along the horizon each day, as if departing, and associated this of your crops to nothing.

Archaeological evidence of our ancestors' preoccupa^ tion with the solstices-and particularly the winter solstice -lias been uncovered at numerous sites, including New- grange in Ireland, Stonehenge in southern England, Machu Picchu in Peru and Chaco Canyon in New Mexico.

Like ancient medics in India and China, Hippocrates saw the turning of the seasons as important to human :alth: 'Whoever wishes to pursue the science of medicine in a direct manner must first investigate the seasons of the and what occurs in them,' he wrote,He advised people :cording to the seasons, what they ate and drank, the type exercise they took, and even how often they had sex, in to keep these humours in balance

. for instance, we know that the sun enables us to manufacture vitamin D in skin, and that levels of it vary over the year; Phototherapy is widely used to treat jaundice in ;wborn babies; light in the blue-green part of the spec- breaks down the bilirubin pigment in the blood that causes it.

Seasonal and daily fluctuations of light and dark - and their impact on our bodies - are increasingly being investigated accepted by modern scientists as well.

These daily fluctuations in our biology are called circadian rhythms

By tweaking our urges, behaviour and biochemistry, they prepare us for regular events in our environment, like mealtimes or getting up in the morning, which are themselves dictated by the daily cycle of light and dark.

If we don't see enough daylight, or we're exposed to too much artificial light at night, our bodies become confused and no longer work as efficiently.

Mounting evidence suggests that our sun exposure over a lifetime-even before were born - may shape our risk of developing a range different illnesses, from depression to diabetes.

when the sunlight hits our skin, our odies release endorphins, the same 'feel good' hormones produce a runner's high.

Meanwhile, dimly lit offices, sunscreen and indoor iving all mean that we're depriving ourselves of the UV our skin needs to synthesise vitamin D, But at least nine-to-five office hours are roughly syn- ;hronised to the day/night cycle.

PHOTOPERIOD Lighting - SEASONS Moments

Over the past two decades, there has been a scientific revolution in the field of chronobiology - which studies :hese cyclical changes in our bodies - with the vital impor- tance of our biological relationship with our nearest star becoming ever clearer. In 2017, the Nobel Prize for medicine was awarded to circadian biologists, in recognition of just important this relationship is to human health. Almost of our genes are under Orcadian control) including ones associated with every major illness investigated so far - including cancer, Alzheimer's disease, type z diabetes, ronary artery disease, schizophrenia and obesity. Disrupt- these rhythms - as we do when we sleep, eat or exercise the wrong time - is associated with an increased risk many of these diseases, or a deterioration of symptoms ssociated with them. What's more, many of the drugs we on in modern medicine target biological pathways that regulated by circadian clocks, which means that they be more or less effective, depending on when we take :hem.

Forging a healthier relationship with light doesn't mean we have to ditch our electronic gadgets and return to the dark ages. But we do need to acknowledge that excessive light at night and an absence of bright light during the day is harmful and so take steps to counter it. We evolved on a rotating planet, when day was day and night was night: it's time to reconnect with those extremes.

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Winter is viewed as a gloomy inconvenience and, rather than getting outside to reap what little daylight there is, we switch the lights on and crank up central heating instead. This may be detrimental to our nental health: exposure to bright light, particularly during early morning, is a tried and tested way of combating the winter blues.

The ancients were right to put the sun at the centre of their world. Sunlight was essential for the evolution of life earth, and it continues to influence our health today. But arkness is also important: the natural cycle of night and that the sun presides over is implicated in everything sleep patterns, to our blood pressure, to our ms. Denying access to this cycle, as we do when we cosset ourselves indoors and spend our evenings under bright irtificial lights, could have far-reaching consequences that we're only just beginning to grasp.

LIGHTS GO OFF AT 22. Bream outstanding.

It's called the suprachiasmatic nucleus (SCN), and it consists of a small cluster of cells in a deeply buried called the hypothalamus: if you drilled a hole between eyebrows, you'd eventually hit it.

The internal rhythms generated by these cellular clocks are called circadian rhythms-from the Latin circa, meaning iround' and diem, meaning 'day'. They help us to prepare for regular events in our environment, which are linked to the revolutions of our planet.

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Orcadian rhythms are thought to have evolved because aligning our activities with the daily light-dark cycle boosts chances of survival

REINDEER

, Arctic reindeer are another example: they appear turn off their circadian clocks during the summer and winter when there is either 24-hour darkness or light. In mmon with many other animals, reindeer also possess a ircannual clock, which means that their biology changes ccording to the seasons: it is another way of anticipating preparing for regular changes in their environment. For instance, reindeer and many other species only give birth during the spring, when their young are most likely to survive; reindeer are programmed to grow new antlers then too.

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puring the 1960s, German researchers led by Jurgen Aschoff and Riitger Wever constructed an underground bunker close to the traditional beer-brewing monastery Andechs in Bavaria, then set about recruiting people to in it. The idea was to see what happened to people's cir- cadian rhythms when they were isolated from external time cues and free to choose when they ate and slept or switched lights on and off. The bunker had no windows and was from traffic. They even wrapped it in copper wire in case electromagnetic forces might influence the ability to time.

They also kept letailed diaries about how they felt during this experience of living 'timelessly*.

Divorced from the outside world, the volunteers were beginning to 'free-run' on their own internal rhythms.5 At the time, schoff and Wever assumed that it was our social inter- with other people that usually kept us synchronised the ^-hour world. But it turned out to be something simpler: light.

turns out that light acts like the reset button on a Stopwatch: it tweaks the precise timing of the master clock SCN), ensuring that it remains aligned with the rising setting of the sun. If you have a long pendulum, then >osure to bright light during the daytime will pull the lands of your clock forward a little bit, so it catches up with the sun; if you have a short clock, it will wind them a little bit, meaning that everyone stays synchronised.

For millennia, the only source of light at night was moon- or starlight - which, although it contains a broad spectrum of colours, is very dim - or the light produced from burning wood, wax and oil. Firelight produces a large amount of light in the red part of the spectrum, but very little blue, and it also tends to be relatively dim, whickn neans that its effect on the circadian system is minimal. Electric light, on the other hand - particularly the LED found in computer screens, and, increasingly* in ceiling lights and street lights - is far brighter and emits a lot more light in the blue part of the spectrum. This means that far of it is needed to change the timing of the clock. This is one reason for the recent concern expressed by scientists

medical professionals about exposure to artificial light at night. For more on the topic of how bright light affects see chapter 3,'Shift "Work'.

BS Whatever it was...

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The body electric

The early 1800s marked a turning point in our relation-

ship with light. Before then, people experienced night in old way, when the only source of indoor light besides yhale-oi) lamps, which were unaffordable for many people and therefore used sparingly

In 1807, the first gas street lights were erected s Pall Mall; by 1820, there were 40,000 of them ipital 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 tend the street lights, which they lit using an oil lamp ttached to a long pole long pole

As Robert Louis Stevenson wrote in his 1878 essay Plea for Gas Lamps':

When gas first spread along a city, mapping it forth evenfall for the eye of observant birds, a new had begun tor sociality and corporate pleasui :eking... Mankind and its supper parties were onger at die mercy of a few miles of sea-fog; sundo longer emptied the promenade; and the day was engthened our ro even1 man's fancy. Hie citv-folk ha of their own; biddable, domesticated stars.2

Some of these gaslights can still be found in isolated ockets of large cities, such as St James's Park in London 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.

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.

Pettit has spent more than a year on board the Interna- tional 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 ument the extent of light pollution and how it's changing due to the growing popularity of LED street lights.

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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- 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! bedrooms.

Some city authorities are starting to take notice. New York and Montreal have altered their plans to install stan- dard 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 Edin- burgh, the street lights have been fitted with shades to direct their glare downwards. Such measures have earned Moffat title of Europe's first 'dark sky town'.

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The researchers have also discovered that daytime light exposure is much higher among the Amish than for most of 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 various rhythms in our bodies - is reduced if exposed to more constant light conditions between daf and night. Such 'flattening' of the circadian rhythm has been associated with poorer sleep, and is observed in man/ ill- nesses, from depression to dementia

During the summer, Amish people are exposed too an average daytime illuminance of 4>ooo lux, whereas the iverage Brit is exposed to 587 lux. During winter, the Amish

experience lower levels of daytime light-around 1,500 lux for us indoor-dwelling Brits, the average daytime illumi nance 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 poorjudge 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 any- thing 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; 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 sup- pression. 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 alert- ness) 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. Xxxxxxxx

Adjusting the light settings on your phone or tablet - or installing an app that automatically filters out blue light after sunser-can help. Even so, most sleep researchers advo- cate 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.

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 ness more directly.

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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 recom- mends an average illuminance of 200 lux in most offices, while for work requiring limited perception of detail, including most factories, it is just iooluxti7 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.

Yet when Figueiro compared workers receiving a 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,’

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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.

There's another reason why Amish are an interesting pop- ulation 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^ They also have very low rates of general depression.

However, it could also be related to their relationship with light. Because their body clocks are more closely aligned with the solar day,

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Shift Work

While shift workers are particularly at risk, few of us manage to maintain our circadian rhythms exactly as they should be.

Life on a submarine is stressful.

to be regularly flying across time zones, or working night shifts, for your internal clocks to become scrambled - and, potentially, for your health to suffer. If it's possible to regu- larise your schedule - which may also mean getting to bed earlier on work nights, cutting down evening light expo- , and trying to get outside more during the daytime- could have tangible benefits for the way you look and feel. And it may also boost your chances of living to a ripe old age, just like Hammv Timmermaa.

Although the high blue-light content of standard LEDs disrupts circadian rhythms when people are exposed to- them at night, LEDs also enable at least some of the effects of daylight to be realistically recreated indoors. Because they are tiny, many different-coloured iEDs can be joined together to vary the shade of the light they produce, enabling the colour and intensity of a lighting system to be adjusted according to the time of day.

For an extra couple of thousand euros, Lowden explained, it would be possible to install a 'circadian light- ing system' that could supply a shot of intense white-blue light to boost workers' alertness at key times, such as the start of a night shift, but also fade to a dimmer, warmer white in the run-up to the shift's end, preparing them for sleep - in this way, the night shift would be more like an afternoon/evening shift, and when the workers got home they would be ready to sleep. Similarly, the intense, blue- white lighting could provide a substitute for sunlight for those working day shifts in the cave-like interior of the control room, keeping them rooted in the 24-hour world.

Florence Nightingale

She emphasised how the morning and midday sun (the very times when hospital patients were likely to be in bed) were of most importance. 'Perhaps you can take them out of bed in the afternoon and set them \>y the window* where they can see the sun,' she suggested. 'But the best rule is, if possible, to give them direct sunlight from the moment he rises till the moment he sets.

A similar thing is happening in developing countries today, and vitamin D deficiency - caused by smog, sun avoidance and clothing which completely covers the skin - is a growing problem,. even in sunny countries in the Middle East, Africa and parts of Asia.

J3y the middle of the nineteenth century, rickets was widespread in urban Britain and in other rapidly industrial- ising countries. A survey by the British Medical Association in the 1880s highlighted the urban nature of the problem: agricultural areas. Many who flocked to the booming cities found themselves living in cramped and gloomy condi- tions, and the burning of coal for the new industries - not to mention the production of gas for lighting - casta thick blanket of smog that smothered out sunlight and made spending time outdoors unpleasant. Children played in narrow alleyways, between tall buildings, further isolating them from any sunlight that did penetrate through- Add nutritional deficiencies because of poverty into the mix and a legion of bowed, deformed skeletons was the result.

It was in the late 1880s that an English missionary called Theobald Palm suggested that sunlight deficiency was the cause.

llie breakthrough came in 1925, when an American doctor called Alfred Hess discovered that feeding rickety rats the skin of humans or calves that had been irradiated with UV light cured them of their rickets.7 The mystery curative factor it contained was eventually characterised as vitamin D.

By the end of the 1920s and into the 1930s, sunlight was being touted as a cure for, well, pretty much every wish to obtain a general idea of the powers of the sun, and to know the names of the various diseases it benefits, buy a medical dictionary and memorize the names of all healers, truly an "elixir vitae*'? Sunlight had hit the main- stream, and suntans were to become a must-have fashion accessory.

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And on 28 May and 11 July, the towering pillars of glass and concrete neatly frame the setting sun-a phenom- enon dubbed 'Manhattanhenge' that draws thousands of tourists and office workers out on to the streets to observe it.

The shimmering towers of Marfan are impressive to behold, reflecting sun and sky in their substance, as many do. But on the ground, it's a different story. As the city grows upwards, New Yorkers are progressively being deprived of their lunchtime dose ot sunshine as their public outdoor spaces are plunged into shade.

If you're looking for a case study on the role of sun- light in MS levels, you could look at its mysterious boom in sunny Iran, a country that, theoretically, you would expect to have relatively low levels of the disease.

Of particular relevance to multiple sclerosis, vitamin D also appears to stimulate the development of regulatory immune cells, which can prevent immune reactions from spiralling out of control. Low vitamin D during pregnancy has been associated with an almost doubling in the risk of the baby develop- ing multiple sclerosis in later life;11 while young adults with high vitamin D levels are at reduced risk of the disease.

The last Shah of Iran, Mohammed Reza, who ruled

rhe country from 1941 until 1979, had an inclination for European sporrs cars, racehorses and American actresses, and he wore Western clothes; while actresses and pop singers were often photographed in miniskirts and bathing suits. All of that changed with the Islamic revolution of 1979* From then on, men were told to dress conservatively? and women were forced to wear long, loose garments, cover their hair and veil their faces - on pain of arrest by the morality police. Skin previously drenched in sunlight was suddenly covered up.

Currently; vitamin D deficiency is high among the general Iranian population, and significantly morepromi- nent among women and children.

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The trouble is that at latitudes above 37°, which includes anywhere north of San Francisco, Seoul or the Mediterra- neafl Sea, and in most of New Zealand and parts of Chile and Argentina in the southern hemisphere, the amount of vitamin D synthesised during winter months is negligible. In the UK, we can only make it between late March and September, which makes us reliant on reserves of vitamin D built up during sunnier months, as well as dietary vitamin p from sources like oily fish, egg yolk and mushrooms.

Subsequent experiments confirmed it. If you expose somebody to the equivalent of around 20 minutes of British summer sunlight, they will experience a temporary drop in blood pressure that continues even after they step indoors

In higher latitude countries such as Britain, the UV index reach 6 on a sunny day in late April, and it may climb as high as 7 or 8 during midsummer.

Taken together, these new scientific findings suggest that our transition from predominantly outdoor- to indoor- based lifestyles in recent decades could be having consequences -including raising our risk of MS, as those studies in Iran have hinted. They also illustrate the pitfalls of trying to replace sunlight, which has shaped lution over hundreds of thousands of years, with a single supplement - vitamin D. Although vitamin D is clearly important to many aspects of our health, and supplements are one way of ensuring that those of us living at high lati- tildes get enough of it during the winter months,24 they are no substitute for adequate daylight exposure throughout the year (we also need bright daylight to keep our interna] for us, but too little also puts our health at risk. The sun should feature in our daily lives, as it has for millennia.

The release of i?-endorphin in response ro sunlight could therefore go some way towards explaining why being in the sun feels so good, and why we so crave it when the sun grows weaker during winter,

In the UK, one in five people claim to experience the winter blues, but only z percent suffer from true SAD

And regardless of what causes winter depression, bright light - particularly when delivered in the early morning - seems to reverse the symptoms.

The inhabitants of Rjukan, in southern Norway, have a complex relationship with the sun. 'More than anywhere else I've lived, they like to talk about the sun; when it's coming back; if it's a long time since they've seen the sun,' says artist Martin Andersen. 'They're a little obsessed with it.'

It was a bookkeeper called Oscar Kittilsen who first came up with the idea of erecting large, rotatable mirrors on the northern side of the valley, from where they 'would first collect the sunlight and then spread it like a headlamp beam over the town of Rjukan and its merry inhabitants'. The three mirrors, each measuring 17 m2, stand proud upon the mountainside above the town. In January, the sun is only high enough to bring light to the square between and welcoming. Stepping into the sunlight after hours in shade, I am reminded of just how much it shapes our perception of the world. Suddenly, the colours are more vibrant, the ice on the ground sparkles, and shadows ppear where none stood before.

Following the early experiments with Herb Kern, inter- est began to grow among psychiatrists about the potential for bright light as treatment for SAD. Sweden was a particu- larlv vigorous early adopter, although here they went one step further, dressing patients in white robes and sending them into communal light rooms. the Ijusrum (light room)

SAD no daylight

Iceland

Skammdegisthunglyndi - the heavy mood of the short days.

found char the further north we

went, the more positive people's mindsets were,' she says. 'In the south, people didn't like winter nearly as much. But across the board, liking winter was associated with greater life satisfaction and being wiling to undertake challenges that lead to greater personal growth,

Midnight Sun

Older than the Egyptian pyramids, and contempora- neous with the very first phases of Stonehenge, Dowth is one of several passage tombs, mounds and stone circles that were constructed in Ireland's Boyne Valley around 3200 bc. The three largest - Newgrange, Knowth and Dowth - are aligned with sunrise or sunset at key turning points of the year, and decorated with rock art, at least some of which depicts the sun. with the midwinter sunrise and sunset, while Knowth is aligned with the spring and autumn equinoxes. This could be a coincidence, except that at Newgrange there's a delib- erafe opening called a roof-box, which - for 17 minutes on the shortest day of the year - allows light from the rising sun way and penetrate the back chamber, lighting up a sun-like three-spiral design engraved on the rocky back wall. Gaining access to the annual spectacle at Newgrange is, quite literally, a Iotrerv: each year rens of thousands of visitors compete for just a handful of places in the tomb at midwinter sunrise-and I wasn't one of the luckv winners. However, far fewer people realise that a similar phenom- enon takes place at Dowth, and that (for now at least) you can enter the tomb on the afternoon of the winter solstice and observe it. Unlike Newgrange, there are no tour buses, no glitzy visitor centre marking Dowth's location; only a wooden stile and a small sign on the grassy verge of an Irish countrv road.
At 2 p.m., the event we're waiting for begins. A shaft of light from the passageway begins to penetrate the chamber. The light has a golden quality, and forms a long rectangle on the floor, which grows and slowly creeps backwards as the sun sets lower in the sky. Its progress is impeded slightly by an unkempt cluster of conifers outside, which cast deli- cate shadows that dance and flicker on the floor. At 3 p.m. - about an hour before sunset -the sunlight hits a series of large stones lining the back wall, illuminating a profusion of marks pecked into them, which are clustered into shapes, squiggles and sun-like spirals. One of the stones curves outwards, reflecting the sunbeam into another wedge-shaped recess, where a solar 'wheel' and spiral are carved. There's an awed hush, and we stand in meditative silence, watching the dancing shadows, until at 3*3o p.m., the sunlight begins to retreat from the chamber, slowly plunging it back into darkness.

This phenomenon occurs at Dowth from late Novem- ber to mid-January, but the strongest illumination occurs on the winter solstice, when the sun is at its lowest ebb. We can only speculate about what our ancestors had in mind when they built this place. Possibly, this sight wasn't intended for the living at all: it was a signal to the dead that it was time to leave their tomb-certainly the journey through the dark tunnel into the light has strong connotations of birth

Certainly, the winter solstice must have been a time of great hope: that light would triumph over darkness, and that life would conquer death-

Particularly in Scandinavia, the midsummer sol- srice rivals Christmas for its festivities, as people gather together on midsummer's eve to sing songs., light fires and party through the night.

puring summer, the light in polar regions is said to be like no other light on earth: 4lbu ge: drugged by it, like when you listen to one of your favourite songs. The light there is a mood-enhancing substance,' wrote the American mountaineer Jon Krakauer who summited Antarctica's highest peak, Mount Vinson, during the summer

The problems of prolonged exposure to bright light are perhaps most striking at the earth's extremes: in Antarctica, sleep problems are so common that workers have their own name tor the mild state of delirium they cause: 'Big Eye\

the run-up to his death in March 1911, the Antarctic explorer Captain Robert Falcon Scott admitted in his diary to losing track of the days as he and his fellow explorers dragged their sleds through the whiteness.

What the experiences of people living and working at these extreme latitudes teach us is that our biology functions best when there is neither too much light nor too much darkness in our environment. What we're looking for, it seems, is a sweet spot where both can flourish; a yin vang that brings harmony to our internal chemistry It is easy to suggest, a little harder to implement, but worth the effort. And no more so than for sick and trail people, for whom maintaining a strong circadian rhythm sleep could spell the difference between life and death.

Light cure

Scientists have unpicked many of the mechanisms through which light interacts with our eyes and skin ro fine-tune our internal biology. They have established the enormously significant role that circadian rhythms play in preparing our bodies for the various challenges that day and night throws at them.

Therefore, if we can strengthen these rhythms and let sunlight back into our lives (while taking care not to burn the skin) it should make a tangible difference ro our health and welfare. It's unlikely that strengthening our circadian rhythms is going to cure serious diseases such as demen- ria or heart disease - but if implementated over the long term, it could reduce our risk of developing them, and if we already have them, reduce the severity of some symptoms.

University of Loughborough researchers monitored patients coming in and leaving the unit, and discovered that for every 100 lux increase in illuminance, patients' length of stay was reduced by 7.3 hours. While other studies have shown that having a view also makes a difference, they cal- culated that light played a more significant role in speeding recovery,

If our circadian rhythms have this powerful an impact on our immune systems, rhen the disruption of these rhythms recovery from serious illness. By the same logic, it's possible that stabilising or strengthening these rhythms, by expos- ing people to bright light during the day and darkness at night, could enhance their recovery.

Cameras tracking where residents sit during the day have also found that they tend to congregate where the light is brighter.

The ISS is darker than most indoor working envi- ronments on earth, and the frequent rising and setting of the sun complicates things still further: 'If you go to the cupola right before going to bed, and you look out and see sunrise or sunset, you just got 100,000 lux,' says Smith L- Johnston, a medical officer and flight surgeon based at the Johnson Space Center in Houston. 'You're not going to be able to sleep for two hours because you will just be buzzed.'

Clocks for society

Today, Bad Kissingen is pushing the discovery of a dif- ferent kind of time; it has rebranded itself as the world's first Chronocity - a place where internal time is as import- ant as external time, and sleep is sacrosanct.

pad Kissingen has always been about healing and health, he reasoned; so what better way to heal our modern society than by bringing it back into contact with natural light and sleep.

schools should start later, children educated outdoors where possible, and examinations not conducted in the mornings; businesses be encouraged to offer flexitime, allowing later chronotypes to work and study when they felt at their best; health clinics could pioneer chronotherapies, tailoring drug treatments to patients' internal time; hotels might offer guests variable meal- and check-out times; and buildings should be modi- fied to let in more daylight.

However, it wasn't until 1907 that an Englishman called "William Willett setf-PUblished a pallet, The Waste of Daylight, and persuaded politicians to argue his ideas about changing the clocks through the British parliament. Willett 'has the monument be would have wished in the thousands of playing-fields crowded with eager young people every evenins throughout the summer and one of the finest epitaphs that any man could win: He gave more light to his countrymen’

Expecting people to wake at 6-30 a.m. and then mentally sharp when they arrive at work at 8 a.m. or 9 a.m. is therefore figuring against nature to some extent

Logical reasoning tends to peak between ioa.m. and noon; problem-solving berween noon anD 2pm wiii mathematical calculations tend to be fastest around 9 pm

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They have convinced me that it is possible to forge a healthier relationship with night and day without return- ing to a pre-industrial past, where the extremes of light and dark restricted our productivity and made it uncomfortable to live-even difficult to survive-at certain times of year. We need to spend a greater proportion of our daytimes outdoors, to reap both the biological benefits of sunlight on our skin, and to realign our internal clockwork.

; or it's just not possible to eat break- fast next to a large east-facing window, bathed in bright morning light So, we must also strive to find new and inno- vative ways of brightening our homes and workplaces - as well as dimming our lights in the evenings.

Already, lighting companies are tweaking indoor light- ing ro make it more like daylight, but in the future lighting may be tailored to the individual: sensors will detect how much light people have been exposed to over the previous 24 hours, possibly in connection with software used to track their sleeping patterns. The lighting at home and at work will then be adjusted to optimise an individual's circadian rhythms and keep them entrained to the sun.

spawned from a revolving planet, itself shaped by starlight. And although we create our own electric stars to light the night, our biology remains tethered to a monarch mightier than them all: our sun.