AT FIRST blush, Prometheus’s punishment might seem like an overreaction. For the minor crime of giving humanity a bit of fire to kick-start civilisation, he was sentenced to an eternity of getting his liver pecked out by an angry bird.
But maybe the Greeks were on to something with their punishment for messing with the natural order of light and dark. With night-time now optional and our metropolises growing ever brighter, we’ve begun to realise that a 24/7 society has consequences. It affects sleep patterns, creates health problems and just generally alters performance and mood in a bad way.
The levels of artificial light in our society show no signs of abating, yet they may not need to. The latest research is showing that if we could just change the type of light, we could restore our natural sleep cycles and reverse artificial light’s negative effects. We might even be able to improve on what nature gave us.
Advertisement
Fire aside, the modern-day lighting revolution began with the 20th century and Thomas Edison’s incandescent bulb. In terms of the light they give out, bulbs have not changed much since then. All the work has essentially gone into making bulbs more efficient, something the compact fluorescent bulb certainly is. But light from these bulbs does not so much illuminate our surroundings as irradiate them with their harsh, blueish glare. Plus their mercury content has raised questions about how to dispose of them safely.
So the past few years has seen the rise of the light-emitting diode (LED) bulb. Because they emit light only in a very narrow part of the electromagnetic spectrum, LEDs lose far less energy to heat than incandescents do. Yet they have some sleep researchers worried, because the spectrum of light from white LEDs contains a strong peak of blue light (see illustration). “Blue light is bad at night,” says Abraham Haim at the University of Haifa, Israel, who studies the effects of artificial light.
That’s because light does far more than simply enable us to see the world: it also helps regulate hormone levels and circadian rhythms. Vision evolved because of the need to know if it was day or night, says Steven Lockley, a sleep researcher at Harvard Medical School in Boston. To differentiate night from day, light-sensitive melanopsin receptors in our eyes tune our sleep-wake cycle to match the 24-hour day. These receptors respond to all visible light, but they’re most sensitive to blue, which peaks in natural sunlight at midday.
When it detects this blue-tinged light, the body responds by suppressing production of the sleep-inducing hormone melatonin, and that makes us feel alert. We are highly sensitive to blue, and although these receptors are in the eyes, they respond even if you can’t actually “see” blue. From midday to dusk, the blue in natural light fades, to be replaced by a reddish tint that stops the suppression of melatonin, reduces our alertness and allows us to get ready for sleep.
At least, this is the cycle we have evolved to follow. But in a 24/7 society saturated in artificial light, our natural systems go adrift. Constant, unchanging light – including blue light at night – prevents the melatonin system from sensing the darkness it needs to promote sleep. This leaves us sleep-deprived and that has health effects, which show up most clearly in night-shift workers. “Good epidemiology shows that women with night shifts have a 50 per cent increase in breast cancer,” says Lockley. “Light at night might be a risk factor,” because it reduces melatonin, which can suppress tumours (see Â鶹´«Ă˝, 7 May 2011, p 44).
Shift workers are worst affected, but most of us are exposed to artificial lighting long after the sun has set. “As a consequence, in society, we are chronically sleep-deprived,” says Lockley. There is evidence that disrupted melatonin production can cause a lot of problems. “You are more likely to be prone to cardiovascular disease, obesity, cancer and gastrointestinal problems,” says Mariana Figueiro of the Lighting Research Center at the Rensselaer Polytechnic Institute in Troy, New York. “Both fixed white LEDs and fluorescent lighting are bad,” says Haim. “Using them at night is polluting our environment.” And it’s not just humans who suffer from the disruptive effects of artificial light – some alarming effects have been seen in animals too (see “In a Bad Light”).
However, where some see a problem, others have begun to see an opportunity. So far, artificial light has been designed according to a one-size-fits-all paradigm, only emitting one constant white light. Simply using LEDs to simulate earlier types of light misses the point, says Fred Schubert, also at Rensselaer. Instead, he thinks we should use LEDs to design light sources “that have not been considered possible” before. Do that, and LEDs offer the opportunity to eliminate the problems with artificial lighting.
LEDs to the rescue
Instead of fighting our body’s response to different colours of light, we can use LEDs to take full advantage of it. The ideal is a tunable white light created from a combination of red, green and blue LEDs, Lockley says. The different hues can be amplified and suppressed over the course of the day to mimic the natural variations in sunlight, thereby keeping our circadian clocks in sync. That kind of colour flexibility, he says, “will let us do things therapeutically with LEDs that we never could do with their predecessors”.
NASA has already started to investigate this possibility, since it has a particular interest in its employees’ circadian rhythms. Astronauts, after all, are the ultimate shift workers. They float around in a world where the sun rises and sets every 90 minutes as the International Space Station orbits the Earth. Space offers no margin for error, so they must be at peak performance every moment they are awake. However, the combination of erratic natural light and steady fluorescent light they receive on the space station means that they often struggle to get 6 hours of sleep in 24, never mind the recommended 8 ().
Worried that woozy astronauts could make dangerous mistakes, NASA wants to get their sleep back on track. That’s why George Brainard, a sleep specialist at Jefferson Medical College in Philadelphia, is testing colour-tuned LED lighting in lab replicas of the four sleeping compartments on the space station. “We can dial in thousands of colour combinations,” he says, to assess what blends and schedules are best for helping astronauts perfect their sleep patterns.
For example, a red-rich mode should help them prepare for sleep as they do personal chores and relax. A yellow-tinged morning light will help them wake. A third setting would provide blue-tinged, alertness-boosting lighting during work periods. NASA plans for the lights to replace the fluorescent ones now in their sleep quarters in 2015.
“Having a single light source with multiple settings and tunable colour is a new thing. This is early days, and it’s going to get more sophisticated,” Brainard says. But he is already looking further ahead, and expects LEDs to drive a “revolution in architectural lighting” in the next 10 to 20 years.
Because if we have the technology to mimic the subtle variations of sunlight, why stop there? We could go one better than nature and create artificial light purpose-built to optimise mood and performance.
“We could go one better than nature and create artificial lights that optimise our mood and performance”
Blue light, for example, is bad at night, but at other times it can cheer you up. “Blue light is good in the day,” says Haim. “We need to suppress melatonin or we would be depressive.” Indeed, people with seasonal affective depression are effectively treated with therapeutic doses of exactly the blue-rich bright light that mimics the midday sun. Blue is what’s important, though, according to researchers in the Netherlands, who recently found that just ramping up the blue content of an ordinary white light had the same mood-boosting effects, but they happened faster (BMC Psychiatry, vol 11, p 17).
The rest of us can benefit, too. In one recent US military study, soldiers were instructed to do a series of tasks under four different workplace lighting conditions. After a few hours under a dim fluorescent light, their mood was depressed and their performance slipped. Under an LED bulb tuned to mimic the blue hue of midday sun, however, their mood improved significantly and they did better on the tasks ().
And there’s no reason to stay in nature’s schema. Some intriguing effects are starting to show up, including the suggestion that bright red light also boosts mood ().
Some industries could benefit enormously from influencing the mood of their customers, one of them being airlines. Boeing’s new 787 Dreamliner jet is designed for long-haul flights, and in an attempt to provide a more pleasant experience, the company has chosen a special kind of LED light. Instead of the standard white LED, which is actually a blue LED covered with a phosphor layer that converts part of the blue to yellow, it will be using expensive lights that combine red, green and blue light and can be tuned to emit different quantities of each. The cabin will have a “warm reddish” tint, so that “people will arrive at their destination feeling more refreshed”, says Blake Emery, a director at Boeing.
However, these lights are far too expensive at the moment for home lighting, mostly because green LEDs are much less efficient than their blue and red counterparts. Each type of light comes from combining different metals and semiconducting materials, and with the combination needed to produce green light the more power it receives, the less green light comes out. This effect is called droop, and for a long time no one understood why it happened, but it seems that Schubert and his colleagues at Rensselaer have now found out why (). They identified how the electrons leak out of the thin layer of semiconductor when they should be releasing their energy as light. This causes the strong currents that would otherwise produce intense light to eject electrons from the critical layer before they can generate photons. If manufacturers can redesign their LED structures to plug that leak, a solution is just around the corner, and RGB lights will be commercially available in the not-too-distant future, not just for homes but also for streets and offices.
“You ultimately want a smart lighting system,” Brainard says. “You walk into your house, the sensor system detects who you are and what you need, and adjusts the lights accordingly.” Your alarm clock could turn on your bedroom light in yellow wake-up mode in the morning. Night workers, on the other hand, could come home to melatonin-releasing red. We’d all get enough sleep, but you could change the settings if you needed to work late or were throwing a party.
Your new lights will do far more than Thomas Edison could have imagined, and with them a modern Prometheus could create a more civilised human civilisation. Perhaps the solution to the problem of artificial light is to make light not less artificial but more so.
In a Bad Light
Joe Ritter didn’t care about turtles at first. He cared about stars. So he was worried about the white LEDs that were replacing the old, orange-yellow sodium street lamps all over the US. Install these brighter lights on Maui, the Hawaiian island where he works and it would “devastate astronomy” in one of the world’s most important research sites.
But when Ritter, a physicist at the University of Hawaii Institute for Astronomy, started investigating solutions, he found something much more alarming: the artificial light was devastating wildlife. Endangered Hawaiian seabirds like the Newell’s shearwater and the dark-rumped petrel were dropping dead in their hundreds. Upon leaving the nest for their first flight, baby birds are supposed to head towards the bright reflection of light on water. But with street lights shining brightly too, the fledglings get confused. They fly towards the lamps and end up circling them until they .
Baby green sea turtles are also drawn to the artificial light, after hatching on the beach. Heading in the opposite direction from the sea, the turtles become easy prey for predators or get killed as they cross busy roads.
And cute baby animals aren’t the only kind that are affected. A recent study showed that intensely bright street lights have increased the population of woodlice, harvestmen, ants and beetles, even during the day. (). Both of these problems are worse under the blue glare of LED lamps than they were under the orange glow of sodium lamps.
And for all the damage they do, Ritter says, they don’t even help us see any better. The intense blue does more to regulate mammalian circadian rhythms than it does to aid visual acuity (see main story).
To solve the problem, Ritter has developed a light with a unique spectral mix that drastically reduces the blue light content. The lights have been in production for six years and are now installed in Hawaii, where they lessen the effects of light pollution on animals. “If we can save the turtles and save astronomy – that’s a win,” says Ritter.
