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.
“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 . One possibility — supported by research — is that having the light on disrupts the quality of sleep, but surprisingly this study did not find that result while monitoring the people in the lighted room. In fact, the participants generally reported that they thought they slept fine.
However, Zee and her team believe that this small amount of light was enough to activate the sympathetic arm of the autonomic nervous system — what’s responsible for the body’s fight or flight response. This is supposed to cool down during sleep as the body moves into a parasympathetic state, when the body’s heart rate and respiration decrease.
“There’s a lot of coordinated actions that have to occur in order for us to get a good night’s sleep and the autonomic nervous system balance regulates that,” says Colwell.