Written by Anne Aulsebrook (@AnneAulsebrook), PhD Candidate, University of Melbourne
for the National Science Communication Challenge
Bright lights, bigger cities.
They are keeping us awake - and other creatures, too.
Have you ever forgotten to turn on your headlights at night?
Our roads are often so brightly lit that you don’t need headlights to see.
Artificial light helps us to feel safe at night, and it extends our hours of productivity.
But artificial light is allowing light to exist at unprecedented times, and intensities.
Less than two hundred years ago, the brightest light at night was moonlight.
Today, more than 60% of Australians live under skies that are always brighter than a full moon.
All animals sleep, often for a large part of their lives.
Many, including humans, tend to sleep at night. But artificial light at night can make it harder to get a good night’s sleep.
Light makes us feel more alert, keeping us awake. Light is also an important biological signal, which indicates time of day.
When light is detected by specialised cells in the eye's retina, it suppresses production of the hormone melatonin.
As a result, melatonin levels are usually low during the day, and high at night.
This melatonin “rhythm” regulates other day-night (circadian) rhythms, including sleep. However, even dim artificial light, like light from a nearby streetlight, can suppress night-time melatonin production.
Artificial light at night then confuses day-night rhythms, affecting the timing and quality of sleep.
Without enough sleep, we are less attentive, more accident-prone and at higher risk of heart disease.
Sleep is even important for song-learning in songbirds, and courtship in fruitflies.
Sleep deprivation, caused by light at night, could have serious consequences for humans and wildlife.