Circadian phase advance: going to bed earlier, waking up earlier. Blue blockers at sunset, bright light at sunrise. Flying east. Autumn.
Circadian phase delay: staying up late, sleeping in. Flying west. Spring. Using smart phones, tablets, and iPads in bed at night. Light pollution.
Relative to adolescents, infants and children are circadian phase advanced. This is part of what is fueling the movement to delay high school start times. Kids are mentally better prepared to work later in the day. With early school start times, performance is down in the morning, but they kill it on video games after school. Delaying start time by an hour won’t totally fix this, but could help.