How important is light for sleep-wake cycles?
Your brain's "master clock" is sensitive to light, explains Michael Timothy Smith, MA, PhD, director of the Behavioral Sleep Medicine Program at Johns Hopkins University. He discusses how that clock affects your sleep.
Up next
Jun 1, 2015
Why do so many people have trouble sleeping?
Why is sleep so important for the mind and body?
How many hours is considered enough sleep?
Jan 14, 2026
What happens to memory during sleep?
Can you catch up on sleep?
What is considered a good night's sleep?
How does sleep affect chronic pain?
What are good bedtime rituals to prepare for sleep?
What happens to the eyes when a person is in REM sleep?
Does alcohol interfere with sleep?