Research suggests that light looms as large in our well-being as sleep. Rosie Blau consults experts in California and Japan

From INTELLIGENT LIFE magazine, May/June 2014

Every summer when he was a boy, Satchin Panda would stay on his grandparents’ farm near Chandipur on the east coast of India. He lazed in a hammock, caught fish in the lake and climbed trees to pick mangoes. His grandfather spent most of his 91 years there, working on his 20-acre plot. He produced almost everything his wife and eight children needed. They cooked whatever he grew; they bought salt and sold a little rice. “He did that for his entire life,” says Panda. “He travelled more than 100km from his home perhaps eight or nine times.”

Panda’s home now is thousands of miles awaya four-bedroom house on the edge of a canyon near San Diego, California. He lives off his mind rather than his muscles and regularly jets around the world for work. “If I’m within a five-hour flight of India,” he says, “I go and see my Mum and my sister.” But the shift is more profound than one of geography. Panda commutes by car, works in a basement and spends most of his leisure time between four walls too. Within two generations, he and his family have moved inside out of the daylight, from rising with the sun to being woken by an alarm, from ending their day near dusk to choosing how lateand how bright—to make their night.

For most of human history we have marked time by the solar cycle. We evolved to spend hours outside every day; bedtime came soon after sunset and the night was black. Now most of us pass our waking hours inside offices, factories, schools, shops, hospitals and nurseries, in cosy but often dim rooms with sealed windows and little natural light. Then, as day starts to fade, we flick a switch and bring it back. Compared with the past, our working hours are gloomy and our nights dazzling. 

We have been slow to recognise the positive link between light and health. Over the past 40 years the sun has been the enemy: the medical establishment has warned us off the ultraviolet rays that contribute to skin cancer. But now scientists have a new worrythat getting too little daylight may also do long-term damage to our health.

Satchin Panda (right) is one of these scientists. A professor of molecular biology, he works at the Salk Institute for Biological Studies in La Jolla, California, where he does research on the body clock that every living being has inside them. “My grandpa was almost religious about taking an hour’s nap by day,” says Panda. “He slept nine to ten hours a night.” Such habits would be inconceivable for Panda himself. But he is far from complacent about the contrast between their lives: he fears that when we override the light-dark cycle of the natural world, we are disrupting the internal workings of the human body. By robbing ourselves of daylight we may be losing something more fundamental.

Moving off the land and lighting up the night have been integral to the narrative of human progress. When people first domesticated fire they changed their lives for ever: day did not end at sundown. They enlivened dark caves, and later lit homes with candles and oil lamps. After the incandescent bulb was commercialised in the 1880s, some feared electricity as a silent, god-like force that might bend the laws of nature. Others clamoured for the bright, white, steady filaments that burned reliably even when the fickle sun did not. Less than a century and a half on from Edison’s eureka moment, we live in a 24-hour society unimaginable without such brilliance.

The illumination of the world has brightened our lives in more ways than the simply physical. Now we can watch the news, work on our laptops, make a Facebook friend, play video games, eat pancakes, buy shoes or download a novel at any hour of the day or night. We are undaunted by the rising or setting of the sun. Now we are all masters of the light.

One consequence is that we sleep less and less. A few hundred years ago, we probably conked out for up to ten hours a night, depending on the season. When researchers give people the opportunity to rest as much as they want over a few months, most young adults eventually stabilise around 8.5 hours, older people a little lower. On average Americans sleep about 20% less than a century ago, according to the National Sleep Foundation, and a third have six hours or fewer. These trends are repeated across the developed world.

This matters. If we don’t sleep, we die. Literally. Rats kept from sleeping drop dead within weeks. Being tired makes us less productive, more forgetful and apt to make mistakeshuman error in the wee small hours contributed to the Exxon Valdez oil spill, and the Chernobyl and Three Mile Island nuclear accidents. Sleep affects the body’s internal workings too. It enhances our immune system, so that, when deprived of it, we are not only liable to catch a cold, but also more susceptible to some types of cancerand if we already have cancer it will probably grow faster. We are more likely to have heart attacks or become depressed. We over-eat when tired, and because our metabolism alters too, we are far more prone to obesity and diabetes.

We also inflict these ills on our children: worldwide they sleep for an estimated hour and 15 minutes less each school night than a century ago; in America only a third of high-school students get at least eight hours on a week-night. But whereas tired adults are sluggish and lethargic, kids become hyperactive and distractiblewhich may be one reason that more than one in ten children in America are now diagnosed with attention deficit hyperactivity disorder, the symptoms of which are remarkably similar to sleep deprivation. What would be the effect if, rather than popping pills, we sent them outside to play each morning and put them to bed earlier?

The medical benefits of sleep are well established but the science of light is much newer. We have only recently started to notice the benefits of boosting our light exposure by day and asked why they occur. Some consequences are fairly predictable: in brighter environments we are more alert, complete visual tasks better and make fewer mistakesa study of call-centre workers in Sacramento found that those with a good window view from their workstation processed calls 6-12% faster than those without. Other responses are more surprising. In 1999 consultants studied an unidentified retail chain in America with 108 similarly laid out stores in a single region and found that people spent 40% more in the shops with skylights than in those lit only by electricity.

What is most startling is the way our bodies respond to light. Gloomy winter days are known to trigger a form of depressionseasonal affective disorderwhich can be reversed if the sufferer sits by a large lightbox every morning. But light eases other forms of depression too: an Italian study found that bipolar patients in east-facing hospital rooms stayed nearly four days fewer than those in west-facing ones. Even physical conditions respond to doses of daylight: people recuperating from spinal and cervical surgery in bright rooms took fewer painkillers every hour; in sunny Alberta in Canada female heart-attack patients treated in an intensive-care unit recovered faster if they were exposed to lots of natural light. Mortality in both sexes is consistently higher in dull rooms. But why is it a matter of light or death?