Loading Professor Cain’s just-published data suggest humans may be way more sensitive to light than previously thought. If that is true, normal light at home is enough to suppress the melatonin that puts us to sleep. Hence the gloom in Professor Cain's home. Artificial light might even be making us fat and diabetic, a group of leading scientists controversially argue. “Even at really low levels of light, we are essentially tricking our bodies into thinking it is day when it is night,” says Professor Cain, a researcher at Monash University.

“For the average person, we expect they are massively suppressing their melatonin all the way up to bedtime.” Our bodies keep time using circadian clocks in our brains. The clock-cycle controls many aspects of our lives: hormone-release, hunger, sleep. Before the invention of the light globe, it was largely set by the rise and fall of the sun. Pubs and bars with neon lights in the French Quarter, New Orleans USA. Could our artificial lights be doing us damage? Credit:Shutterstock Modern humans live under artificial suns and Professor Cain fears that may be messing with our clocks. A painstaking study published in science journal PNAS this month provides tantalising new evidence for his theory.

His team put people in a room at night-time and took hourly measurements of their melatonin, the hormone our body secretes to make us sleepy. Then they exposed them to different levels of light. The effects were much bigger than they expected. Professor Sean Cain in his lab. Credit:Justin McManus A dim reading light delayed the release of melatonin by 77 minutes on average. A standard overhead light delayed it by almost two hours. "It makes it a little harder to go to sleep. And it would shift your clock to an earlier time – so the next night it is harder to get to sleep."

Illustration: Matt Golding Credit: The team tested 55 men and women. Surprisingly, they all had different reactions to the same level of light. Some people were getting their sleep-signal suppressed by lights dimmer than a candle. What does that mean for human health? Here, Professor Cain moves from hard data to hypotheticals. If humans are extremely sensitive to light, it is possible our artificial lights are scrambling many people's body clocks. For most people that is tolerable, but those with high light sensitivity could be left “living in a state of perpetual jetlag,” Professor Cain says.

This ties in with an earlier study from the same team: in a small experiment, antidepressants were shown to dramatically increase light sensitivity. Could it be they improve mood by helping the circadian clock accurately set itself? “This is growing,” says Professor Cain. “There is a growing realisation that, at the very foundation of general health, is circadian health. Almost every tissue in your body has circadian rhythms, and when they are disturbed, the whole system starts to fall apart.” There is a growing realisation that, at the very foundation of general health, is circadian health. Professor Sean Cain A second paper, published in the Journal of Internal Medicine this month, takes the theory a step further. If a correctly set bodyclock is integral to human health, and we live in a world of artificial light that is messing with that bodyclock, is it possible many of the problems that plague modern society – such as diabetes and obesity – are linked to light?