In this episode, I host Dr. Samer Hattar, Ph.D., Chief of the Section on Light and Circadian Rhythms at the National Institute of Mental Health. Dr. Hattar is a world-renowned expert on how viewing light at particular times adjusts our mood, ability to learn, stress and hormone levels, appetite, and mental health. We discuss how to determine and use your individual light sensitivity to determine the optimal sleep-wake cycle for you. We also discuss how to combine your light viewing and waking time with the timing of your food intake and exercise in order to maximize mental and physical functioning. Dr. Hattar is credited with co-discovering the neurons in the eye that set our circadian clocks and regulate mood and appetite. He explains why even a small shift in daylight savings leads to outsized effects on our biking because of the way that our cells and circadian clocks integrate across many days. And he offers precise tools to rapidly adjust to jet lag, shift work, and reset your clock after a late night of work or socializing. This episode is filled with cutting-edge data on the biological mechanisms of human physiology and practical tools for people of all ages. Read the full show notes for this episode at hubermanlab.com.Thank you to our sponsorsAG1: https://athleticgreens.com/hubermanLMNT: https://drinklmnt.com/hubermanlabWaking Up: https://wakingup.com/hubermanMomentous: https://livemomentous.com/hubermanTimestamps00:00:00 Introducing Dr. Samer Hattar, Ph.D.  00:02:33 Sponsors: AG1, LMNT & Waking Up00:06:15 Light, Circadian (24-hour) & Circannual (365-day) “Photoentrainment”  00:14:30 Neurons in Our Eyes That Set Our Body Clocks: Similar to Frog Skin  00:18:55 What Blind People See  00:20:15 When, How & How Long to View Light for Optimal Sleep & Wakefulness  00:30:20 Sunlight Simulators, Afternoon Light Viewing, Naps  00:33:48 Are You Jet Lagged at Home? Chronotypes & Why Early Risers Succeed  00:38:33 How to Decide Your Best Sleep-Wake Schedule; Minimal Light Test  00:42:16 Viewing Light in Middle of Day: Mood & “Light Hunger”  00:44:55 Evening Sunlight; Blueblocker Warning  00:48:57 Blue Light Is Not the Issue; Samer’s Cave; Complete Darkness  00:53:58 Screens at Night  00:56:03 Dangers of Bright Light Between 10 pm and 4 am: Mood & Learning  01:01:05 The Tripartite Model: Circadian, Sleep Drive, Feeding Schedules  01:05:05 Using Light to Enhance Your Mood; & The Hattar-Hernandez Nucleus  01:07:19 Why Do We Sleep?  01:08:17 Effects of Light on Appetite; Regular Light & Meal Times  01:18:08 Samer’s Experience with Adjusting Meal Timing  01:22:51 Using Light to Align Sleep, Mood, Feeding, Exercise & Cognition  01:30:15 Age-Related Changes in Timing of Mental & Physical Vigor  01:31:44 “Chrono-Attraction” in Relationships; Social-Rhythms  01:33:40 Re-setting Our Clock Schedule; Screen Devices Revisited  01:37:50 How Samer Got into the Study of Light  01:39:33 Clock Gene mRNAs & More Accurate Biomarkers  01:41:08 Light as Medicine  01:42:48 ADHD (Attention-Deficit Hyperactivity Disorder)  01:43:35 How to Beat Jet Lag: Light, Temperature, Eating  01:50:44 Vigor: The Consequence of Proper Timing  01:52:15 Waking in the Middle of the Night: When Your Nightly Sleep Becomes a Nap  01:54:10 Melatonin, Pineal Calcification  01:55:25 Our Seasonal Rhythms: Mood, Depression, Lethargy & Reproduction  01:59:08 Daylight Savings: Much Worse Than It Might Seem  02:05:27 Eye Color & Sensitivity to Light, Bipolar Disorder  02:09:28 Spicy Food, Genetic Variations in Sensory Sensitivity  02:10:52 Synthesizing This Information, Samer on Twitter, Instagram  02:13:00 Conclusions, Ways To Support the Huberman Lab Podcast & Research  Disclaimer & Disclosures