For thousands of years, man lived in synchronicity with day and night patterns, his wakefulness and sleep tracking light and dark. Then he invented artificial light and suddenly our rhythms were out of sync. We extended the day, and got a lot more done—but with impacts to our physiology that we're still only beginning to understand.
Potentially, some of these are quite troubling, as a new paper explains. On the milder end of things, the light we encounter after dusk disrupts our circadian circuitry, so that we don't sleep as well as we might. At the most serious end, this failure to "reset" our bodies has implications for all kinds of disease.
Electric light disrupts "all aspects of our endogenous circadian rhythmicity; its intensity and spectral content are often not adequate during the day for proper circadian resetting, and are too much during the night for a true ‘dark’ to be detected," says the paper, which is authored by Richard Stevens, a professor at the University of Connecticut, and Yong Zhu, an associate professor at Yale. "This can lead to ‘circadian disruption’ compromising general well-being and perhaps increasing risk of a variety of specific diseases."
Although the links between electric light and cancer, diabetes, and obesity are not proven, unwanted light is known to affect our hormone levels and the way our genes express themselves. For example, lighting at night has been shown to reduce melatonin hormones that protect against certain cancers, at least in rats.
Stevens has long proposed that night light might increase breast cancer risk and he's keen to raise awareness of general consequences of unnecessary after-hours light. "There is no question that we are changing our physiology," he says in an interview. "Too much electric lighting is bad for our well-being. It's not optimal to our health."
Interestingly, modern energy-efficiency lightbulbs may be worse than old incandescent ones. That's because they emit more light in the blue part of spectrum that keeps us most awake. The same is true for LED lights that are now replacing traditional streetlights in cities. In effect, we might saving money on electricity, but perhaps harming our well-being in the process.
In our homes, Stevens recommends we choose light towards the red end of spectrum, that we dim things as much as possible, and that we avoid computers just before bed. Again, these emit blue light. The professor himself uses a red light in his bathroom, so his sleep isn't broken when he uses the facilities at 3 a.m.
More broadly, research into the impact of electric light suggests we should take light pollution more seriously than we do. It isn't only something for star-gazers to be irked about. Potentially, when we don't turn out the lights in office blocks, we're doing more than simply wasting energy and contributing to climate change.
"There is no excuse to leave the lights on," Stevens says. "We need night. We evolved for 3 billion years with it. If you want to go to a rock club with bright blue lights, that's fine. But don't impose [your problem] on everybody else in society."