Jet-lag, as the brain scrambles to adjust to crossing many different time zones of light and dark, puts the brain in conflict with the person’s normal sleep patterns. For some it can take a day for every time zone crossed, often causing problems with effective thinking and efficient performances. Similar symptoms can occur when an individual must work rotating shifts or when sleep times differ radically on weekends, as the brain tries to adjust to shorter, longer, or irregular hours. Some teenagers tend to experience a sleep-phase delay. Their melatonin levels naturally rise later at night (compared with many children and adults), which can cause adolescents to feel alert later at night and making it difficult for them to fall asleep before 11:00 pm or midnight. Sleep deprivation, compounded by early school start-times, can negatively influence life in general, and learning in particular. Keeping lights dim as bedtime approaches and/or wearing special glasses to block LED light from electronic devices may help, as can exposure to bright light as soon as possible in the morning.