What the screens research shows, and what it does not

Chang AM, Aeschbach D, Duffy JF, Czeisler CA (2015). Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences, 112(4), 1232 to 1237 doi

Reading on a bright light emitting device in the evening delayed sleep, shifted the body clock later, and left people less alert the next morning, compared with reading a printed book. The limits are important. It was a small study run in a laboratory, the devices were used at high brightness for several hours under controlled conditions, and the design cannot separate the effect of the light from the effect of what people were reading. It supports the claim that screens late at night affect sleep. It does not by itself say anything about a phone glanced at for ten minutes.