A gloomy conclusion: home lighting may be messing with your sleep

For hundreds of thousands of years, the rhythm of our days was set by the rise and fall of the sun.

As darkness fell, our melatonin levels rose, sending us to sleep. At dawn, the sun’s rays pushed down melatonin levels again, rousing us from our slumber.

Now, our lives run to the ceaseless hum of the electric bulb. A new study by researchers in Australia suggests this is having a big effect on the rhythms that dictate when we sleep, and when we wake.

The researchers found the average Australian home’s lighting was so bright it suppressed melatonin by nearly 50 per cent. Those with the new energy-efficient LED lights being promoted by governments were even brighter.

“Modern light is kind of like junk food. We didn’t evolve to deal with it, so we make bad decisions when it comes to consuming it,”
said Associate Professor Sean Cain, the study’s lead author.

Light is a drug, a stimulant that is going to keep you from sleeping.

Associate Professor Sean Cain

The study, published in Scientific Reports this month, is the culmination of a seven-year research project led by Monash University-based Professor Cain.

His team first showed humans are far more sensitive to light than scientists assumed.

Then they showed people with depression have poor light sensitivity – potential evidence that depression may be linked to disrupted circadian rhythms.

“This new study is a culmination of everything – how we live our modern lives now in this twilight region, where it’s dim in the day and bright at night,” Professor Cain said.

Troubled by his own results, Professor Cain has taken to living in gloom, turning off his house lights after dark. His new study suggests he may be onto something.

First, the team measured the effect of light on melatonin levels in 62 people – important because everyone has a different level of light sensitivity. Then the subjects were fitted with tiny light meters that tracked how much light they were exposed to over four days.

Half the homes tested were so bright they would suppress 50 per cent of their owners’ melatonin.

“That sleep-promoting signal is cut in half,” said Professor Cain. “You’re tricking your clock into thinking it’s not as late as it is.”

Homes with energy-efficient LED lights were nearly twice as bright as those with older-style lights. Worse, LEDs typically generate more blue light than lightbulbs, which has been independently shown to effect sleep.

And people who experienced more light than usual before bed were more likely to have sleep problems.

“This study shows that the lights people choose can have real impacts,” said Anne Aulsebrook, a researcher on sleep and light at the University of Melbourne.

Dr Aulsebrook studies the effect of city lights on wildlife. She has consistently found the same thing: when exposed to light, birds sleep less.

But Professor Cain’s study does not provide absolute proof that taking in too much light impairs sleep. It could also be that people who struggle to sleep tend to stay up later, exposing them to more light.

“There is a bit of evidence to suggest that would be the case,” said Leon Lack, a sleep and body clock researcher at the Adelaide Institute for Sleep Health. “But we cannot really infer cause and effect.”

Nevertheless, there is some evidence that if you’re struggling with sleep, darkening the house may be worth a try. In a small study, researchers found just a week camping in the Rocky Mountains of Colorado reset people’s melatonin cycle to sunrise and sunset.