Using Light to Optimize Health | Huberman Lab Essentials
These notes were generated by AI and may contain inaccuracies.
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, a professor of neurobiology and ophthalmology at Stanford School of Medicine. Light has powerful effects on many aspects of biology because it translates into electrical signals in the brain and body, hormone signals, and cascades of biological pathways that change the genes cells express throughout the lifespan.
Light is electromagnetic energy that causes reactions in cells, such as ripening fruit from sunlight.
Physics of Light
Light has many different wavelengths. Imagine a prism splitting white light into a rainbow: reds, oranges, greens, blues, purples. Different wavelengths penetrate tissues to different depths. Every biological function of light involves absorbance, reflectance, or light passing through cells or compartments.
Three Primary Ways Light Impacts Biology
- Photoreceptors in eyes: Rods (elongated) and cones (triangular).
- Skin surface (epidermis): Keratinocytes and melanocytes; light exposure activates genetic programs leading to tanning.
- Every cell in the body: If light accesses bone, bone marrow, heart, liver, spleen cells, it changes their function for better or worse. Deep organs like the spleen respond indirectly.
Light on eyes is absorbed by intrinsically photosensitive ganglion cells (melanopsin cells), containing opsin that absorbs short-wavelength light from sunlight. These communicate to brain stations connecting to the pineal gland (pea-sized in brain center), which releases melatonin.
Light activates these cells, shutting down melatonin production. Melatonin communicates average light in the environment. In northern hemisphere, more melatonin in winter than summer, creating a calendar system based on light and hormone journey around the sun. Environment converts to internal signal via melatonin, aiding sleep.
I am not a big fan of melatonin supplementation because levels in most supplements are superphysiological and can have effects beyond sleep.
Endogenous melatonin (naturally produced) has regulatory and protective effects:
- Regulatory: Positively impacts bone mass; suppressive on gonad maturation (ovaries, testes) during puberty—high levels reduce testicle volume, sperm/testosterone production, egg maturation. Children's high melatonin delays puberty appropriately. Powerful modulator of placental development—pregnant individuals should consult OB/GYN before supplementation due to fetal/placenta effects.
- Most effects reversible.
Hormones like melatonin cause slow modulatory effects; light changes cell/tissue/organ function via this transducer.
Recommendations for Melatonin Regulation
Get outside during long days of summer/spring. In winter, more indoor time is normal/healthy unless suffering seasonal affective disorder (SAD). For SAD, get bright light early morning/throughout day (see episode on mood/circadian rhythms). Modulate indoor/outdoor time seasonally if not depressed.
Light powerfully inhibits melatonin. Middle-of-night bright overhead lights plummet melatonin to near zero, disrupting nightly signal. Occasional ok, but habitual disrupts brain/body timing info.
In animals/humans, UVB light (short-wavelength, from sun/artificial sources) on skin (not eyes) triggers testosterone/estrogen increases and mating desire.
Key Study: "Skin Exposure to UVB Light Induces a Skin-Brain-Gonad Axis and Sexual Behavior" (Cell Reports, Cell Press). Used mice (gene knockouts) and humans (men/women).
- UVB on skin increases testosterone/estrogen quickly, maintaining proper ratios in males/females.
- Mice: More mating, increased gonadal weight (testes/ovaries).
- Humans: Increased aggressiveness, passionate feelings, changed perceptions of others.
- Females: Enhanced follicle growth/egg maturation (fertility indices).
Protocol: 2-3x/week, 20-30 minutes sunlight on as much body as reasonable.
Pain tolerance higher in longer days via UVB to skin/eyes.
Study 1: "Skin Exposure to Ultraviolet B Rapidly Activates Systemic Neuroendocrine and Immunosuppressive Responses"—one UVB exposure changes hormones/neurochemicals like corticotropin-releasing hormone, beta-endorphins (endogenous opioids for pain countering/psychological soothing).
Study 2: "A Visual Circuit Related to the Periaqueductal Gray Area for the Antinociceptive Effects of Bright Light Treatment" (Neuron, Cell Press). Periaqueductal gray (midbrain) releases endogenous opioids (beta-endorphin) reducing pain perception (not blocking harm signals).
- Eye melanopsin cells → brain → opioids.
Protocol: 20-30 min UVB (sunlight preferred) 2-3x/week. Clouds allow more photons than indoor lights. Chase sunlight. Never look directly at painful-bright light; indirect ok. Eyeglasses/contacts focus light to retina cells. Sunglasses/windows/windshields filter UVB. Avoid blue blockers daytime/outdoors (block needed short wavelengths); use evenings for sleep.
Consider clothing for skin exposure (e.g., shorts/T-shirt vs. covered). UVB year-round beneficial (per chronobiology director Samar Hatoum, NIH), unless skin/eye damage risk. For winter lows, use SAD lamp or inexpensive LED panel.
Blind/low-vision with eyes retain melanopsin benefits. Consult ophthalmologist/dermatologist if retinitis pigmentosa, macular degeneration, glaucoma, skin cancer prone.
UVB communicates external info to organs like spleen (infection combat). Brain-spleen connection: Eye UVB → sympathetic nervous system (autonomic, controls heart/breathing/immunity) → spleen deploys immune cells/molecules (killer T-cells, B-cells, cytokines).
Fewer summer infections because better combat, not fewer pathogens.
Winter Tool: Prioritize UVB for spleen/sympathetic activation.
Wound healing faster with UVB. Hair/skin/nails grow/turn over faster in longer days.
Study: PNAS—eye melanopsin cells critical for stem cell turnover in skin, hair, nails.
Neural circuit from melanopsin cells bypasses circadian areas, targets perihabenular nucleus for dopamine/serotonin/opioids. Night activation (10 p.m.-4 a.m.) reduces these, worsening mood/depression.
Tool: Get daytime UVB; avoid artificial UVB 10 p.m.-4 a.m. to preserve dopamine/mood.
Avoid becoming neurotic about UVB exposure to the point of not using lights at all. Position artificial lights in the evening low in your physical environment. Melanopsin cells reside in the lower half of the eyes and view the upper visual field, designed to respond to sunlight from above. Dim these lights as far down as safely possible.
Red light and near-infrared light (longer wavelength than red) pass through the epidermis into the deeper dermis layers, changing metabolic function of cells. For acne, sebaceous glands in the dermis produce skin oil near hair follicles, which have portals that allow infections. Melanocytes and stem cells for skin and hair follicles are also in the dermis.
Low-level burn from long-wavelength light activates stem cells to produce new cells, clearing lesions and replacing them with healthy skin. This works for wound healing, reducing scars, and removing pigmentation patches.
Long-wavelength light penetrates deep into skin and individual cells, accessing organelles, particularly mitochondria that produce ATP. Aging, metabolically active cells accumulate reactive oxygen species (ROS), reducing ATP production.
Red light activates mitochondria, increases ATP, and reduces ROS directly or indirectly. ROS cause cellular damage, death, and inhibit cell function. Red and near-infrared therapies for healing skin, improving quality, removing lesions, scars, or pigmentation are grounded in biology of light-mitochondria-ROS interactions—not pseudoscience.
Light activates pathways driving cell death or rejuvenation by improving mitochondrial function and ATP.
Recent studies show red and near-infrared light enhance function of cells for vision and cognition. Data from Dr. Glenn Jeffrey at University College London, working on visual neuroscience, emphasize red/near-infrared for restoring neuronal function with age.
Jeffrey Lab published two human studies: subjects (20s or 40+ years) viewed 670 nanometer red light (appears red) at safe distance (~1 foot) for 2-3 minutes/day. One study: 12 weeks; other: couple weeks.
In 40-72 year olds (not <40), improvements in visual acuity (resolving fine detail) and Triton exam (short-wavelength cones for green/blue): 22% improvement—exciting result.
Aging loses rods, retinal cells, ganglion cells. Rods/cones are most metabolically active cells, accumulate ROS. Red light reduced ROS in rods/cones, rescued short/medium-wavelength cone function, reversing neuronal aging.
Observed reduction in drusen (fatty/cholesterol deposits accumulating with age in eye). Neural retina is highly vascularized, metabolically active. Red/near-infrared reduces drusen accumulation, cholesterol deposits, and ROS to improve neuronal function.
Studies exciting but recent—more data needed. Key features:
- Exposure early in day, within first 3 hours of waking.
- Use red light panels/sources in 670nm red + 790nm near-infrared range (often combined commercially).
- Not so bright it damages eyes: safe if not painful, no squinting/closing eyes. Retinal neurons do not regenerate.
- Most panels too bright close-up, designed for skin with eye protectors blocking red light.
- Set at comfortable distance (not forcing squint/turn away) for 2-3 minutes/day.
Red light beneficial late day, middle of night (e.g., shift workers). Use red light bulbs—no panel needed.
Study: "Red light, a novel non-pharmacological intervention to promote alertness in shift workers." Red light (sufficiently dim) does not inhibit melatonin, does not increase cortisol at night. Late-night cortisol (e.g., 9-10pm) linked to depression, mental health issues.
For night wakefulness (shift work, studying, childcare): red light preferred, as dim as possible while allowing activities.
Light changes activities of cells, organelles, organs—locally and systemically. Thank you for joining this deep dive into phototherapies, the power of light to modulate biology and health. Thank you for your interest in science.
Keep Andrew Huberman in your library
Save the videos and channels worth coming back to, and find them again in one place.
