In the morning, they'd give both groups a big dose of sugar to see how well their systems responded to the spike. 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. The next night, half of them slept in a more illuminated room (the light was placed overhead). For the study, all the participants spent their first night sleeping in a mostly dark room. '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.

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. 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.

Phyllis Zee, senior author of the new study and director of the Center for Circadian and Sleep Medicine at Northwestern University. 'I was surprised that even this fairly, I would say, small amount of light just getting through the eyes to the brain still had such notable effect,' says Dr. New research suggests that one night of sleep with just a moderate amount of light may have adverse effects on cardiovascular and metabolic health. Many Americans sleep in a room that's punctuated with some form of artificial light - whether it's coming from a TV, a jumble of electronics or an intrusive streetlight.

Turning off the lights and closing the curtains isn't exactly a catchy, new sleep hygiene hack, but this common sense advice is gaining even more scientific credibility.

Sleeping with tv on effects