This TED-Ed video explains the science behind sleep schedules and why changing them can be challenging. It introduces the circadian rhythm, the body’s internal clock that controls sleep, wakefulness, and energy levels. The video shows how light exposure, especially sunlight in the morning and screens at night, strongly influences this rhythm. It also discusses chronotypes and why teenagers often prefer later bedtimes. Finally, the video offers realistic strategies such as gradual adjustments, consistency, and healthy routines to successfully shift sleep patterns over time safely.