This resource explores the concept of the circadian rhythm, which is the body's internal clock that regulates sleep and wake cycles. It explains how light and darkness influence our biological processes, the role of melatonin as a sleep hormone, and the effects of blue light from screens on our ability to fall asleep. It also addresses the consequences of sleep debt on physical well-being, cognitive function, and mood. The document includes scenarios, analyses, and reflections aimed at understanding the relationship between technology use and biological needs for sleep.