The screen light imposes drop in melatonin production, thus its concentration.
The pineal gland feels the initiation of the screen light as early morning hours with sunrise, continue to sense “daylight”/screen light through the night in 12-13 hours (see graph) including the real following daylight hours, thus the circadian rythme is pulled back by several hours, starting production of melatonin in the end of this usual 12-13 hours laps.