Teenagers are not lazy. Their biology has shifted them to a different time zone. And sunlight is the only thing that pulls it back. At age 1, roughly 70% of children are natural morning risers. By age 16, only 5% are. Not because of phones. Not because of discipline. Because of puberty. Researchers studying 25,000 people found that the circadian clock shifts progressively later from childhood through adolescence. It peaks at its latest around age 20 for women and 21 for men. Then it gradually drifts earlier again for the rest of life. The mechanism is hormonal. Pubertal hormones delay the clock directly. The shift shows up across cultures and countries, and it tracks with biological puberty stage, not social behavior. Morning sunlight is the strongest signal that pulls a drifted clock earlier. For adults, consistent morning sun keeps the clock anchored to the real day. For teenagers, whose clocks have biologically shifted to run later, morning light is working against a stronger hormonal current. It still helps. But it has to compete. Evening light makes everything worse. Any bright light at night pushes an already-late clock even later. Screens are not equally disruptive for everyone. For a teenager at their biological extreme, they are adding fuel to a fire that is already burning. The question is not why teenagers sleep so late. It is what kind of light they are living in, and whether any of it is helping. ☀️

“A new report echoes a chorus of scientific research saying that permanent Standard Time is the best solution for eliminating twice-yearly clock change.”