Episode 68: Using Light (Sunlight, Blue Light & Red Light) to Optimize Health| Huberman Lab

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Key Takeaways

  • Light can change the genes that the cells of the body express directly and indirectly
  • There are more than 100 years of science supporting the use of specific types of light to support the health of the brain and body
  • Different wavelengths of light impact our tissues at different levels – shortwave light (e.g., blue, UV) doesn’t penetrate beyond the top surface of the skin; longwave light (e.g., red) penetrates deep through the skin to bone
  • Think of light as a communicator of what’s going on in the environment around you and either taken at the surface or deeper and passed off as instructions to other areas or organs of the body
  • Tip: if you wake up in the middle of the night, try not the flip on a light (or use longwave light) so you don’t disrupt melatonin levels
  • Sunlight and day length can impact the melatonin pathway and directly trigger hormone pathways (testosterone and estrogen), desire to mate, and mating behavior
  • Using light to optimize testosterone and estrogen: get about 20 minutes of light exposure to as much skin as possible, 2-3 times per week minimum
  • Experiencing pain? Go outside & get direct UVB light on the skin and in the eyes! On longer days or in bright light environments, we tolerate pain (nociception) better
  • Benefits of direct UVB exposure on eyes & skin: enhanced immune function, increased turnover (growth) of stem cells in hair and nails, sleep regulation, faster wound healing, increases in hormones
  • Tip for shift workers or people awake at night for childcare, etc.: if you need to be awake at night, red light is the best choice because it will not inhibit melatonin or increase cortisol
  • Obvious but worth stating: when we talk about light exposure to the eyes, it shouldn’t be painful to look at or force you to squint or turn away – it’s too bright to safely look at if that’s the case


Dr. Andrew Huberman, Ph.D. is a Professor of Neurobiology and Ophthalmology at Stanford University School of Medicine. His lab focuses on neural regeneration, neuroplasticity, and brain states such as stress, focus, fear, and optimal performance.

In this episode, Andrew Huberman describes the mechanisms by which different wavelengths of light impact the cells, tissues, and organs of the human body, and how specifically timed light exposure of specific wavelengths can be used to improve sleep, and enhance alertness, modulate hormone levels, and improve mood.

Host: Andrew Huberman (@hubermanlab)

Physics Of Light

  • Light is electromagnetic energy
  • Light travels in many different wavelengths and affects the brain, body, environment, etc.
  • There are wavelengths of light that are not visible to the human eye (e.g., UV light)
  • Light impacts us at different levels, i.e., wavelengths
  • Different wavelengths of light can penetrate tissues to different depths
  • Shortwave light (e.g., blue, green, UV light): doesn’t penetrate tissue easily beyond the top surface of the skin
  • Longwave light (e.g., red): can penetrate way beyond the top layer of tissue and maybe even down to bone or bone marrow
  • Time of exposure to different types of light can change the way the cells and organs of the bodywork

Biology Of Light

  • Every cell in the body will have an altered function (for better or worse) when accessed by light
  • The impact of light on the body is uniquely important – more so than drugs, sounds, food, touch, anything: particular wavelengths of light can be used to stimulate the function of particular organelles within particular cells within particular organs of the body
  • Absorption of light energy: certain pigments in object receiving the light energy are going to absorb particular wavelengths of light
  • Absorbance properties of surface receiving the light indicative of whether light penetrates or bounces off
  • Rods in the eye are used to see in low light conditions
  • Cones in the eye see color (baring colorblindness) and can absorb different wavelengths
  • Surprisingly, rods and cones demand the most energy out of all the cells in the body
  • Skin pigment melanocytes absorb UV light and create changes in skin pigmentation
  • A calorie is essentially food’s light energy: the heat at which a certain food burn gives you a sense of how much energy it can provide your body (i.e., calories)
  • Impact of light can be direct (e.g., light onto skin or photoreceptors in the eye) or indirect (e.g., light hits photoreceptors then starts a domino effect to downstream organ or cell) – but all starts with a particular wavelength of light being absorbed
  • Example of the rapid effect of light on the body: if you go into a bright room or are exposed to bright light shortly after waking, it mimics the wake-up effect similar to that of being dunked in very cold water

Slow Integrating Effects Of Light On The Body & Melatonin

  • The body takes in information about light and slowly changes the way biology works
  • Even one exposure to UVB light changes hormones release
  • On longer days or in bright light environments, we tolerate pain (nociception) better
  • Circannual rhythm: rhythms that exist within the body and hormone release throughout the day and night as an indicator of where you are in the 365-day calendar
  • The light activates cells which shut down the production of melatonin
    • On short days: melatonin release is longer
    • On longer days: melatonin release is shorter
  • On average, melatonin is an indicator of how much light is in the environment
  • Endogenous melatonin has two categories of effects: (1) regulatory effects; (2) protective effects
  • Regulatory effects of melatonin: positively impact bone mass by the production of osteoblasts, maturation of gonads and ovaries, effects on the central nervous system in terms of waking up or making us sleepy  
  • Protective effects of melatonin: activate the immune system, potent antioxidant properties
  • It’s critical to get the proper amount of sunlight to our eyes each day
  • Light powerfully inhibits melatonin – but our bodies are accustomed to the natural changes in melatonin in relation to the natural calendar rhythms
  • Avoid melatonin supplementation! Try other approaches to regulating sleep before consuming over the counter melatonin because the amount in the supplement is several times our natural, endogenous level
  • Melatonin inhibits testosterone and estrogen output from the testes and ovaries which is critical to the desire to mate
  • Skin is a hormone-producing and hormone influencing organ: skin exposure to shortwave light (e.g., blue, UV) can trigger increases in testosterone and estrogen and the desire to mate
  • People from places with lower light throughout the year or lighter skin experience more significant increases in testosterone with light exposure
  • Seasonal effects of testosterone: testosterone levels appear lowest in the winter months and highest in June, July, August, September
  • Our bodies are better at combating infection during the summer & spring months because the increased UVB light enhances spleen function

Effects Of Light On Mood

  • Getting as much UVB light in the eyes and on the skin early in the day is critical to sleep, wakefulness, and mood
  • Bright light at the wrong time in the 24-hour cycle can make your mood worse: dopamine output drops, “happy hormones” reduce output
  • UV exposure in the morning and day is important but avoiding light exposure at night is equally critical
  • Avoid shortwave light (blue, UV) exposure between 10 pm and 4 am – or even 8 pm onward if you suffer from depression
  • Even just one night of dim light exposure during sleep (even if it doesn’t wake you up) may impair cardiometabolic function such as increased insulin resistance and decreased heart rate variability
  • During a night of healthy, deep sleep our body transitions through various forms of metabolic function – disruption will affect cardiac function and metabolic light

Red Light, Longwave Light & Longwave Light Therapy (LLT)

  • Redlight therapy & LLT can improve acne and skin lesions by penetrating through the skin and triggering certain biological pathways in a deeper layer which replace damaged skin
  • Light activation drives pathways that either stimulate the death of cells or stimulation of healthy cells that restore youthfulness
  • Important note: LLT for skincare treatments should be hot enough to penetrate the skin but not burn it; therapy should also be targeted and illuminate only patches seeking repair
  • The ability to keep retinal neurons healthy is extremely important – we don’t generate more neurons throughout life
  • Red light may reverse age-related vision loss: exposure to red light within three hours of walking, at a safe distance for a few minutes each day may improve visual acuity and function, particularly rescuing the function of rods and cones
  • Tip for shift workers or people awake at night for childcare, etc.: if you need to be awake at night, red light is the best choice because it will not inhibit melatonin or increase cortisol
  • The exciting potential of wavelength brain stimulation: a pattern of flashing light delivered to the eyes creates a pattern of neuronal firing that triggers molecular which reduce markers and the causes of age-related decline in the brain – and – up-regulation of biological pathways that lead to enhancement of neuronal function


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Notes By Maryann

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