April 1, 2022 – The findings tie into a broader body of evidence that indicates being exposed to light at night may be harmful in a variety of ways and could predispose people to chronic diseases.

The small, 20-person study conducted by Zee and her team at Northwestern was designed to measure the physiological effects of 100 lux of artificial light on healthy adults while they were sleeping. “This is about enough light that you could maybe see your way around, but it’s not enough light to really read comfortably,” says Zee. For the study, all the participants spent their first night sleeping in a mostly dark room. The next night, half of them slept in a more illuminated room (the light was placed overhead).

Meanwhile, the researchers ran tests on the sleepers: they recorded their brainwaves, measured their heart rates and drew their blood every few hours, among other things. In the morning, they’d give both groups a big dose of sugar to see how well their systems responded to the spike.