The circadian clock is most sensitive to light from about 2 hours before usual bedtime and through the night, until about 1 hour after usual wake-up in the morning (this is the sensitive period). Exposure to light during these times will affect when your body naturally gets sleepy and is ready to fall asleep.
The student could tact all items in his backpack and through the sensation reach the cell phone. So he should touch and feel what could be the cell phone.
