Huberman Lab
Essentials: Timing Light for Better Sleep, Energy & Mood | Dr. Samer Hattar
21 Aug 2025
In this Huberman Lab Essentials episode, my guest is Dr. Samer Hattar, PhD, the Chief of the Section on Light and Circadian Rhythms at the National Institute of Mental Health. We discuss how light powerfully shapes mood, sleep, appetite, learning and overall mental health by aligning—or misaligning—our internal circadian clock. We explain practical protocols to support your circadian rhythm, including morning sunlight exposure, dim evening lighting and regular mealtimes. We also discuss strategies to manage jet lag, limit evening screen use, ease seasonal depression and improve focus by syncing light, sleep and food with natural biological rhythms. Read the episode show notes at hubermanlab.com. Thank you to our sponsors AG1: https://drinkag1.com/huberman Eight Sleep: https://eightsleep.com/huberman ROKA: https://roka.com/huberman Timestamps (00:00) Samer Hattar (00:27) Light, Circadian Clock vs Solar Day, Sleep-Wake Cycle (03:20) Eyes, Photoreceptors & Light Entrainment, Blindness, Sleep (06:13) Morning Light, Artificial Lights, Tool: Morning Sunlight Exposure (08:28) Jet Lag Without Traveling, Sleep Issues, Screens, Staying Indoors (09:19) Sponsors: Eight Sleep & ROKA (12:14) Chronotypes, Intrinsic Circadian Rhythms (14:06) Afternoon & Evening Light, Tools: Dimming Lights, Reduce Screen Use (15:57) Light Exposure & Effects on Stress, Mood & Learning, Tripartite Model (19:30) Light & Appetite, Tool: Regular Meal Times (22:39) Using Light to Improve Sleep, Mood & Mental Health (24:20) Sponsor: AG1 (25:42) Jet Lag, Tools: Temperature Minimum; Eat on Local Schedule, Avoid Mismatched Light Exposure (29:15) Sleep Issues, Light-Dark Cycle (30:50) Seasonality, Seasonal Depression; Daylight Savings Time (34:07) Acknowledgements Disclaimer & Disclosures Learn more about your ad choices. Visit megaphone.fm/adchoices
Full Episode
Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health, and performance. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today, I have the pleasure of introducing Dr. Samer Hattar as my guest on the Huberman Lab podcast.
And now my conversation with Dr. Samer Hattar. Samer, thanks for sitting down with me.
My pleasure.
You are best known in scientific circles for your work on how light impacts mood, learning, feeding, hunger, sleep, and these sorts of topics. So maybe you could just wade us into why what the relationship is between light and these things like mood and hunger, et cetera. Sure.
So, I mean, you do appreciate the effect of light for vision. So when you wake up in a beautiful area, beautiful ocean, light is essential. The sunrise, the sunset. So that's your conscious perception of light. But light has a completely different aspect that is independent of conscious vision. And that's how it regulates many important functions in your body.
I think the best that is well-studied and well-known is your circadian clock. And the word circadian comes from the word circa, which is approximate, and DN is day. So it's an approximate day. Why is it an approximate day? Because if I put you or any other human being who have a normal circadian clock in a constant conditions,
with no information about feeding time, about sleep time, about what time it is outside, you still have a daily rhythm, but it's not exactly 24 hours. So it will shift out of the solar day because it's not exactly 24 hours and hence the name circadian.
How does that rhythm show up in the tissues of our body?
It shows up at every level that we know we studied. It shows up at the level of the cell. It shows up at the level of the tissue. And it shows up at your behavior. The most obvious for you is your sleep-wake cycle. You sleep and you're awake and sleep at the 24-hour rhythms. The period length of the sleep rhythm on average is 24.2 hours. So you'll be drifting 0.2 hours every day.
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