Morning light vital for sleep

Riding in school buses in the early morning, followed by sitting in poorly lighted classrooms could explain why students have trouble getting to sleep at night.
Circadian timing affects sleep onset. Delayed sleep onset can reduce sleep duration in adolescents required to awake early for a fixed school schedule. The absence of short-wavelength (blue) morning light, which helps entrain the circadian system, can hypothetically delay sleep onset and decrease sleep duration in adolescents.
To investigate whether removal of short-wavelength light during the morning hours delayed the onset of melatonin in young adults, researchers fitted eleven eighth-class students with goggles that blocked blue light for five days. They found that dim light melatonin onset was significantly delayed (30 minutes) after the five-day intervention, demonstrating that short-wavelength light exposure during the day can be important for advancing circadian rhythms in students.

Teenagers, like everyone else, need bright lights in the morning, particularly in the blue wavelengths, to synchronize their inner, circadian rhythms with nature's cycles of day and night. If they are deprived of blue light during the morning, they go to sleep an average of six minutes later each night, until their bodies are completely out of sync with the school day, the researchers explained.

The above findings provide a possible explanation as to why teenagers stay up too late at night, then fall asleep in class the next morning and perform poorly in scholastic activities.