In our primeval days, nocturnal carnivores prowled through the inky black of our nights. Early humans, unsurprisingly, developed an instinctive fear of the dark. Then, after a long dark age, we took what is widely heralded as our largest evolutionary leap—we learned to control fire.
Banishing the shadows
Yet our fear of what lurks in the shadows has persisted through time. In our modern age, criminals prowl through the dark alleys of our nights. So, in the name of safety, we flood our streets, parks and homes with light. The latest cars sport ever brighter headlights. Indoors we bathe in the brightly lit screens of our televisions and computers.
It is all too easy to forget that our bright nights are artificial. But nature doesn’t forget—our bodies don’t forget—and so we pay the price for what is now known as light pollution.
Pied Piper of the night
The ecosystems of the natural world have evolved around the light of the sun, moon and stars. Light pollution disorients and confuses animals that navigate via these natural light sources.
For example, sea turtles lay their eggs on beaches. When these eggs hatch at night, the hatchlings instinctively move away from the dark silhouette of the sand dunes towards the brighter horizon of the ocean. However, many coastal areas are now populated, and the artificial lights cause the baby turtles to go the wrong way, away from the ocean and often to their deaths.
Aware of the problems for sea turtles caused by light pollution along the Queensland coast, researcher Ruth Kamrowski of James Cook University has been following hatchling disruption during 2011 and 2012. Kamrowski is surveying residents, tourists and local business operators about their use of artificial light, and getting them to think about reducing their use of lights near hatchlings.
In another example, migrating birds navigate through the sky by using the stars and moon. When flying over large cities, they are attracted by the bright lights below. Disoriented, they often collide with brightly lit buildings, or become trapped within the city and die from exhaustion.
On a physiological level, studies have shown that light pollution hampers reproductive cycles and even lowers the immune system in animals. All creatures on this planet are in some way affected by too much artificial light—including us.
Too much of a good thing
The reason light at night can hurt us is rooted in our biological clock, known as the circadian rhythm. The circadian rhythm is an approximately 24-hour cycle that governs the biological processes of life on earth, including humans. It syncs with our outside environment to control the release of different hormones, including melatonin, which causes drowsiness and also suppresses cancer tumours.
When blue spectrum light enters our eyes, photosensitive ganglion cells in our retinas inhibit the pineal gland, the organ responsible for melatonin production. Thus, melatonin levels are typically high at night and low during the day. Melatonin secretion, however, is disrupted by even low levels of light.
Cancer epidemiologist Richard Stevens first made the connection in 1987 when he linked high breast cancer rates among women working the night shift with artificial lighting. Further studies on nurses and airline crews have supported his theory. For men, preliminary evidence suggests light at night increases prostate cancer risk as well.
Recent animal studies have identified the role of melatonin in suppressing cancer cells. For example, cancer tumours grafted onto rats grew significantly larger when perfused with melatonin-depleted blood. Other animal studies have even linked the disruption of the circadian rhythm to depression, weight gain, impulsivity and slower thinking.
In 2007 this snowballing evidence prompted the World Health Organization to add “shift work that involves circadian disruption” as a probable cause of cancer. But, the risk goes beyond shift workers.
According to Shantha Rajaratnam, president of the Australasian Sleep Association and an Associate Professor at Monash University’s faculty of medicine, nursing and health science, it has only been in the past five years that scientists have started to understand how tampering with natural sleeping patterns can affect our physiology. Rajaratnam indicates there was a lack of knowledge about how disrupted circadian rhythms affect the cardiovascular system, the reproductive cycle and the digestive system.
Especially in our over-illuminated cities, simply waking up at night could expose our retinas to light pollution. Our obsession with staring at screens also compounds late-night exposure to light. The latest trend is to use smartphones and tablets late into the night. The LED screens in these electronic devices emit light of the worst kind: blue spectrum light, which suppresses melatonin.
So how do you protect yourself from light pollution? For ideas on limiting light pollution, see the sidebar, “The light stops here.”
Illuminating the light pollution problem
The larger implications of light pollution extend beyond local ecosystems and physical health. With an estimated two-thirds of Earth’s population living under light-polluted skies, over-illumination is an international concern.
In Australia, public lighting is the single largest source of local government’s greenhouse gas emissions, accounting for around 30 to 50 per cent of their emissions. There are 1.94 million public lights—one for every 10 Australians—that annually cost A$210 million, use 1035 GWh of electricity and are responsible for 1.15 million tonnes of carbon dioxide emissions. Many of these fixtures are not targeted on delivering lighting to the ground level uses desired.
Disturbing evidence has emerged showing that light pollution exacerbates air pollution. Each night, compounds called nitrate radicals break down polluting chemicals in the air that form smog and ozone. However, a recent study found that night-time lights significantly slowed down this nightly cleansing.
But perhaps the most dismissed complaint of light pollution is also the most meaningful to future generations. Light pollution is the bane of astronomers who must now retreat to far-flung places such as Hawaii or Chile to observe the stars. Interesting stars and constellations are increasingly more difficult to see with the naked eye behind a veil of orange glow. Many children have never seen the Milky Way.
Dr Barry Clark of the Astronomical Society of Victoria points to the loss of cultural identity of indigenous Australians, with artificial lighting diminishing the celestial features that have given rise to so many Dreamtime creation myths. As he points out, “[a]lready the names of the stars and constellations of almost all of the Australian native language groups have been lost forever.”
For centuries the stars were an integral part of our ancestors’ lives, guiding them through their travels and inspiring ancient mythology. When we gaze upon the heavens, we gain perspective on our existence and feel awe for the mystery of the universe. It would be a shame to lose that.
The light stops here
Limit light pollution in your home and neighbourhood. Here’s how:
- Use a red night light. Light in the red spectrum does not suppress melatonin.
- Keep tech items (laptops, televisions, smartphones) out of your bedroom.
- If you wake up in the middle of the night, do not read or watch TV. Instead practise quiet meditation to lull yourself back to sleep.
- If you do shift work, create a completely dark environment for your sleeping periods and try to keep a regular schedule.
- Get blackout curtains for your windows.
- Ensure your outdoor light fixtures shine downwards, not upwards.
- Cut back on security lighting. If you live outside the city, crime rates are actually higher during the day. Plus, bright lights can actually create an unsafe environment by creating deep shadows and more glare.
- Avoid permanent landscape lighting. There is no good reason to illuminate your hedges at night.
- When purchasing a new vehicle, consider a model with standard halogen headlights rather than xenon, which can be extremely bright to oncoming traffic.
When our internal clocks are disrupted due to increased exposure to light pollution, we may have trouble sleeping. Melatonin can provide short-term relief of temporary insomnia. If you think melatonin may help restore your sleep, discuss it with your health care practitioner.